TC 1-204 NIGHT FLIGHT TECHNIQUES AND

TC 1-204
NIGHT FLIGHT TECHNIQUES AND
PROCEDURES
HEADQUARTERS, DEPARTMENT OF THE ARMY
DISTRIBUTION RESTRICTION: Distribution authorized to US government agencies and their contractors
to protect information and technical data that address current technology in areas of significant or
potentially significant military application. This determination was made on 5 August 1988. Other requests
for this document will be referred to Commander, US Army Aviation Center, ATTN: ATZQ-DAP-SS, Fort
Rucker, AL 36362-5035.
DESTRUCTION NOTICE: Destroy by any method that will prevent disclosure of contents or
reconstruction of the document.
TC 1-204
Training Circular
No. 1-204
* TC 1-204
HEADQUARTERS
DEPARTMENT OF THE ARMY
Washington, DC 27 December 1988
NIGHT FLIGHT TECHNIQUES AND PROCEDURES
TABLE OF CONTENTS
Page
v
PREFACE
CHAPTER 1 NIGHT VISION
1-1. Night Vision Evaluation
1-2. Eye Anatomy and Physiology
1-3. Light Levels
1-4. Vision Types
1-5. Day Versus Night Vision
1-6. Visual Problems
1-7. Dark Adaptation
1-8. Night Vision Protection
1-9. Self-Imposed Stress
1-10. Scanning Techniques
1-11. Distance Estimation and Depth Perception
1-12. Visual Illusions
1-13. Aircraft Design Limitations
1-14. Nerve Agents and Night Vision (Miosis)
1-1
1-1
1-2
1-3
1-4
1-7
1-8
1-8
1-10
1-12
1-14
1-19
1-23
1-23
CHAPTER 2 AVIATION NIGHT VISION AIDS
Section I IMAGE-INTENSIFIER SYSTEMS
2-1. Development
2-2. Operational Theory
2-3. AN/PVS-5 Series
2-4. AN/AVS-6
2-5. Adjustment Techniques
2-6. Operational Considerations
2-1
2-2
2-3
2-7
2-9
2-10
Section II THERMAL-IMAGING SYSTEMS
2-7. Operational Principles
2-8. System Types
2-19
2-19
*This publication supersedes FM 1-204, 11 October 1983.
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2-9. Infrared Characteristics
2-10. Operational Considerations
2-20
2-26
CHAPTER 3 HEMISPHERICAL ILLUMINATION AND METEOROLOGICAL CONDITIONS
3-1. Light Sources
3-2. Meteorological Effects
3-1
3-2
CHAPTER 4 TERRAIN INTERPRETATION
4-1. Visual Recognition Cues
4-2. Interpretation Factors
4-1
4-4
CHAPTER 5 NIGHT OPERATIONS
Section I PREMISSION PLANNING
5-1. Mission Briefing and Debriefing
5-2. Crew Duties
5-3. Common Terminology
5-1
5-1
5-1
Section II PREFLIGHT GUIDELINES
5-4. Preflight Inspection
5-5. Aircraft Lighting
5-6. Aircrew Preparation
5-2
5-3
5-4
Section III NIGHT FLIGHT TECHNIQUES
5-7. Limitations
5-8. Hover
5-9. Takeoff
5-10. En Route
5-11. Landing
5-12. Pathfinder Operations
5-13. External Load Operations
5-4
5-5
5-7
5-8
5-9
5-14
5-15
Section IV EMERGENCY AND SAFETY PROCEDURES
5-14. Basic Considerations
5-15. Electrical Failure
5-16. Airport Traffic Control Light Signals
5-17. Visual Night Signals
5-18. Emergency Landing
5-19. Ground Safety
5-20. Air Safety
5-21. Airspace Management
ii
5-17
5-17
5-17
5-18
5-18
5-19
5-19
5-20
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CHAPTER 6 NIGHT TERRAIN FLIGHT
Section I TERRAIN FLIGHT MODES AND COMMAND CONSIDERATIONS
6-1. Terrain Flight Modes
6-2. Command Considerations
6-1
6-1
Section II PLANNING GUIDELINES
6-3. General Considerations
6-4. Cockpit Teamwork and Coordination
6-5. Aircraft Preparation and Equipment
6-6. Maps and Visual Aids
6-7. General Route and Air Control Point Planning
6-8. Aided Night Mission Map Preparation
6-9. Aided Night Mission Planning and Briefings
6-10. Route Planning Cards
6-3
6-6
6-7
6-7
6-8
6-10
6-10
6-11
CHAPTER 7 MULTIHELICOPTER OPERATIONS
Section I CONSIDERATIONS AND RESPONSIBILITIES
7-1. Planning Considerations
7-2. Supported Ground Unit Commander Responsibilities
7-3. Air Mission or Flight Commander Responsibilities
7-1
7-2
7-3
Section II NIGHT FLIGHT FORMATIONS
7-4. Aircraft Separation
7-5. Night Formations
7-6. Basic Night Formation Considerations
7-7. Formation Takeoff
7-8. Lead Changes
7-9. Formation Changes
7-10. Rendezvous and Join-Up Procedures
7-11. Formation Breakup
7-12. Formation Landing
7-13. Vertical Helicopter IFR Recovery Procedures
7-4
7-4
7-7
7-8
7-8
7-9
7-9
7-9
7-11
7-11
Section III TACTICAL FORMATION FLIGHT
7-14. Free-Cruise Technique
7-15. Movement Techniques
7-16. Crew Teamwork
7-17. Mixed Aircraft Formations
7-12
7-14
7-15
7-15
CHAPTER 8 FIXED-WING NIGHT FLYING
8-1. Preparation
8-2. Taxi, Takeoff, and Departure Climb
8-3. Orientation and Navigation
8-4. Approaches and Landings
iii
8-1
8-1
8-3
8-4
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CHAPTER 9 DROP FLARE EMPLOYMENT
9-1. Target Identification
9-2. Description
9-3. Fuse Setting
9-4. Launch Procedures
9-5. Flight Pattern
9-6. Wind-Drift Correction
9-7. Linear Target Illumination
9-8. Safety Considerations
9-9. Training Program
9-1
9-1
9-2
9-4
9-5
9-7
9-7
9-8
9-9
APPENDIX A. ELECTROMAGNETIC SPECTRUM
A-1
APPENDIX B. I2 SYSTEM COUNTERWEIGHTS
B-1
APPENDIX C. PNVS FLIR
C-1
APPENDIX D. TRAINING PROGRAMS
D-1
GLOSSARY
Glossary - 1
REFERENCES
References - 1
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PREFACE
Night flight has assumed an increasingly important role in Army aviation. The Threat trains
around the clock. To counter it, aviators must be able to conduct operations at night as well as
during the day. Technological advances in night vision devices are enabling Army aviation to
extend its operational capability to a 24 hour-a-day schedule. Ongoing improvements to these
devices will further enhance aircrew performance during night operations.
This publication provides aircrews a comprehensive document on night flight. It is intended to
serve as a reference for night vision, unaided and aided night flight, and night vision training.
The proponent of this publication is HQ TRADOC. Submit changes for improving this publication
on DA Form 2028 (Recommended Changes to Publications and Blank Forms), and forward it
through the aviation unit commander to Commander, US Army Aviation Center, ATTN: ATZQATB-O, Fort Rucker, AL 36362-5218.
The provisions of this publication are the subject of international agreements: STANAG 2999
(Edition One), Use of Helicopters in Land Operations STANAG 3627 (Edition One) and AIR STD
44/34B, Helicopter Day and Night Tactical Formation Flying AIR STD 44/33B, Helicopter Tactical
or Non-Permanent Landing Sites
Unless otherwise stated, whenever the masculine gender is used, both men and women are
included.
This publication has been reviewed for OPSEC considerations.
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CHAPTER 1
NIGHT VISION
Vision is the most important sense used in flight. During day or night, IMC or VMC,
vision is the sense that makes crew members aware of the position of their aircraft in
space. The eyes can rapidly identify and interpret visual cues during daylight. During
darkness, however, visual acuity is decreased proportionally as the level of illumination
decreases. Night vision devices improve the capability of the human eye to see at night.
These devices include the AN/PVS-5 and AN/AVS-6, which are commonly referred to as
I2 systems or I2 devices. Night vision devices also include thermal-imaging systems.
This chapter provides a general discussion of night vision and scanning techniques. FM
1-301 contains additional information.
1-1. NIGHT VISION EVALUATION
a. During the initial flight physical examination, an aviator is interviewed to
determine if he has difficulty seeing at night. If the inter-view indicates the aviator
has adequate night vision, visual testing is not required.
b. The ability to conduct night flight safely is based on how well crew members
can see at night and how well trained they are in using their night vision.
Although the limits of night vision vary from person to person, most crew
members never learn to use their night vision to its fullest capacity. A crew
member with an average night vision capability who uses night vision techniques
is more effective than a crew member with superior night vision who does not.
1-2. EYE ANATOMY AND PHYSIOLOGY
The eye is similar to a camera. The cornea, lens, and iris gather and control the amount of
light allowed to enter the eye. The image is then focused on the retina. Functionally, the
visual receptive apparatus (retina) has two types of cells: the cones and the rods. Vision is
possible because of chemical reactions within these cells. Figure 1-1 shows the anatomy
of the human eye.
a. Cones. Cone cells are used primarily for day or high-intensity light vision. The
concentration of cones in the central retina (fovea centralis) permits high visual
acuity in high illumination. The chemical iodopsin is always present in the cone
cells. Regardless of the ambient light condition, this chemical is readily available
so that the cones can immediately respond to visual stimulation.
b. Rods. The rods are used for night or low-intensity light vision. The peripheral
retina is almost exclusively associated with rods. Peripheral vision is less precise
than central vision, because the rods perceive only shades of gray and vague form
or shape. Rhodopsin, commonly referred to as visual purple, is the photochemical
found in rods. As the light level decreases, the amount of rhodopsin in the rods
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builds and the rods become more sensitive. Rods are about one-thousand times
more sensitive to light than cones. When illumination decreases to about the level
of full moonlight (0.1 footcandle), the rods take over from the cones. The period
of highest light sensitivity usually occurs after 30 to 45 minutes in a dark
environment. The rod cells may become up to 10,000 times more sensitive than at
the start.
Figure 1-1. Anatomy of the eye
1-3. LIGHT LEVELS
Measuring light levels can be complex and confusing. Many different units of light
measurement and terms are used for various scientific, engineering, and industrial
applications. Terms of measurement are usually familiar only to those who work directly
with light measurement problems. Some of the terms important to aircrews are defined in
the paragraphs below.
a. Illumination. Illumination is the amount of light that strikes a surface at some
distance from a source. The common unit of measurement is the footcandle. A
footcandle is the density of light falling on the inner surface of a sphere of 1-foot
radius when a point source of light with an intensity of one international candle is
placed at the center of the sphere.
b. Luminance. Luminance is the amount of light per unit area reflected from or
emitted by a surface. It is an important measurement for visual displays and is
usually expressed in millilamberts or footlamberts. Luminance is frequently called
brightness. However, brightness is influenced by contrast, adaptation, and such
factors as the physical energy in the stimulus. Figure 1-2 shows examples of
luminance levels found during commonly experienced conditions.
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Figure 1-2. Commonly experienced light levels
c. Reflectance. Reflectance is the relationship between illumination reaching a
surface and the resulting luminance. A perfectly diffusing and reflecting surface is
one that absorbs no light and scatters the illumination in the manner of a perfectly
flat surface. Such a surface has a reflectance of 100 percent. If illuminated by 1
footcandle, it would have a luminance of 1 footlambert from all viewing angles.
In actual practice, the maximum reflectance of a nearly perfectly diffusing surface
is about 75 percent.
d. Contrast. Contrast is a measure of the difference in luminance between an
object and its background. Contrast can vary from 100 percent (negative) to zero
for objects darker than their backgrounds and from zero to infinity (positive) for
objects brighter than their backgrounds. Contrast increases when the difference in
luminance between an object and its back-ground increases. Contrast is zero when
the luminance of an object and its background is the same.
1-4. VISION TYPES
The three types of vision are photopic, mesopic, and scotopic. Each type functions under
different sensory stimuli or ambient light conditions. Night vision involves mesopic and
scotopic vision. Photopic vision at night is possible only when sufficient levels of
artificial illumination exist.
a. Photopic Vision. Photopic vision is experienced during daylight or when a high
level of artificial illumination exists. The cones concentrated in the fovea centralis
of the eye are primarily responsible for vision in bright light. Because of the high
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light level, rhodopsin is bleached out and rod cells become less effective. Sharp
image interpretation and color vision are characteristic of photopic vision.
b. Mesopic Vision. Mesopic vision is experienced at dawn, at dusk, and during
full moonlight. Vision is achieved by a combination of cones and rods. Visual
acuity steadily decreases as available light decreases. Color perception changes
because the cones become less effective. As cone sensi-tivity decreases, crew
members should use off-center vision and proper scanning techniques to detect
objects during low light levels.
c. Scotopic Vision. Scotopic vision is experienced under low light levels. Cones
become ineffective, resulting in poor resolution of detail. Visual acuity decreases
to 20/200 or less. This enables a person to see only objects the size of or larger
than the big "E" on visual acuity testing charts from 20 feet away. (A person must
stand at 20 feet to see what can normally be seen at 200 feet under daylight
conditions.) Also, color perception is lost. A night blind spot in the central field of
view appears at low light levels. The night blind spot occurs when cone-cell
sensitivity is lost.
1-5. DAY VERSUS NIGHT VISION
Differences between day and night vision involve color, detail, and retinal sensitivity.
Day vision is superior to night vision in every respect.
a. Color. One major difference between night vision and day vision is that color
vision decreases or is lost at night. With decreasing light levels, the eyes shift
from photopic vision (cones) to scotopic vision (rods). With this shift, the eyes
become less sensitive to the red end of the spectrum and more sensitive to the
blue part of the spectrum, as shown in Figure 1-3. Perception of colors is not
possible with the rods. Colors of nonilluminated objects cannot be determined at
night under very low illumination. Light and dark colors at night can be
distinguished only by the intensity of reflected light. If, however, the brightness or
intensity of a color is above the threshold for cone vision, the color can be
perceived. This is why, for example, signal flares and runway markers can be
properly identified at night.
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Figure 1-3. Photopic (cone) and scotopic (rod) sensitivity to various colors
b. Detail. Perception of fine detail is impossible at night. Under low illumination,
visual acuity is greatly impaired. At 0.1 footcandle (the level of full moonlight),
acuity is one-seventh as good as it is in average daylight. Therefore, objects must
be large or nearby to be seen at night. Identification of objects at night is based on
perceiving generalized contours and outlines, not on small distinguishing features.
c. Retinal Sensitivity.
(1) Another important distinction between night vision and day vision is
the difference in the sensitivity of various parts of the retina. The central
part of the retina is not sensitive to starlight illumination levels. During
darkness or with low-level illumination, central vision becomes less
effective and a night blind spot (5 to 10 wide) develops. This results from
the concentration of cones in the fovea centralis and para fovea, the area
immediately surrounding the fovea of the retina. The central field of vision
for each eye is superimposed for binocular vision. Because the night blind
spot for each eye occurs in the central field of view, binocular vision
cannot compensate for the night blind spot. Therefore, an object viewed
directly may not be detected, as shown in Figure 1-4.
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Figure 1-4. Night blind spot
(2) The night blind spot should not be confused with the physiological
blind spot (the so-called day blind spot) caused by the optic disk. The
physiological blind spot is present all the time, not only during the day.
This blind spot results from the position of the optic disk on the retina.
The optic disk has no light-sensitive receptors. The physiological blind
spot covers an area of approximately 5.5 by 7.5 and is located about 15
from the fovea. Because of the overlap of binocular vision, this blind spot
is normally not noticed unless one eye is not used. The physiological blind
spot becomes an important consideration when monocular night vision
devices, such as the PNVS, are used.
(3) Because of the night blind spot, larger and larger objects will be
missed as distance increases. To see things clearly at night, an individual
must use off-center vision and proper scanning techniques. Figure 1-5
shows the effect of distance on the night blind spot.
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Figure 1-5. Effect of distance on the night blind spot
1-6. VISUAL PROBLEMS
Several visual problems or conditions affect night vision. These include presbyopia, night
myopia, and astigmatism.
a. Presbyopia. This condition is part of the normal aging process, which causes
the lens of the eye to harden. Beginning in the early teen years, individuals
gradually lose accommodation; that is, the ability to focus on nearby objects.
When individuals are about 40 years old, their eyes are unable to reliably focus at
the normal reading distance without reading glasses. As presbyopia worsens,
instruments, maps, and checklists become more difficult to read, especially with
red illumination. This difficulty can be corrected with certain types of bifocal
spectacles that compensate for the inadequate accommodative power of the eye
lenses.
b. Night Myopia. Myopic individuals do not see distant objects clearly; only
nearby objects are in focus for them. At night, blue wavelengths of light prevail in
the visible portion of the spectrum. Because of this, slightly nearsighted (myopic)
individuals will experience visual difficulty at night when viewing blue-green
light that could cause blurred vision. Also, image sharpness decreases as pupil
diameter increases. For individuals with mild refractive errors, vision may
become unacceptably blurred unless corrective glasses are worn. Another factor
to consider is "dark focus." When luminance levels decrease, the focusing
mechanism of the eye may move toward a resting position and make the eye more
myopic. These factors are more important when the aircrew looks outside the
cockpit during unaided night flight. Special corrective lenses can be prescribed to
correct for myopia.
c. Astigmatism. Astigmatism is an irregularity of the shape of the cornea that may
cause an out-of-focus condition. If, for example, an astigmatic person focuses on
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power poles (vertical), the wires (horizontal) will be out of focus in most cases. If
the astigmatism is 1.00-diopter or greater, the aviator must be individually
evaluated before flying with I2 devices that preclude the wearing of eyeglasses.
An example is full-faceplate devices used with daylight filters.
1-7. DARK ADAPTATION
Going suddenly from bright light into darkness is a common occurrence. For example,
people experience this when they enter a movie theater during the day or leave a brightly
lit room at night. At first they see very little, if anything. After several minutes, they can
see dim forms and large outlines. As time goes by, more details of the environment
become apparent as further dark adaptation occurs.
a. Dark adaptation is the process by which the eyes increase their sensitivity to
low levels of illumination. Individuals dark-adapt to varying degrees and at
different rates. During the first 30 minutes, the sensitivity of the eye increases
roughly ten-thousandfold. Very little increase in sensitivity occurs after that time.
b. The lower the starting level of illumination, the more rapid complete dark
adaptation is achieved. For example, less time is required to dark-adapt
completely after leaving a darkened theater than after leaving a brightly lit hangar.
c. Dark adaptation for optimum night visual acuity approaches its maximum level
in about 30 to 45 minutes under minimal light conditions. If the dark-adapted eye
is exposed to a bright light, the sensitivity of that eye is temporarily impaired. The
amount of impairment depends on the intensity and duration of the exposure.
Brief flashes from a white (xenon) strobe light, commonly found on aircraft, have
little effect on night vision because the pulses of energy are so short. On the other
hand, exposure to a flare, a searchlight beam, or lightning may seriously impair
night vision. In such cases, the recovery of a previous maximum level of dark
adaptation can take from 5 to 45 minutes in continued darkness.
d. Night vision devices affect dark adaptation. If a previously dark-adapted crew
member wearing an I2 device removes the device in a darkened environment, a
30-minute dark adaptation level can be regained in about two to three minutes. No
dark adaptation period is necessary before using the I2 device. Vision with I2
devices is primarily photopic, but the low light levels produced by I2 devices do
not fully bleach out rhodopsin. Use of the device does not seriously degrade dark
adaptation.
1-8. NIGHT VISION PROTECTION
Night vision should be protected when possible. Some of the steps crew members can
take to protect their night vision are described below.
a. Equipment.
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(1) Sunglasses. Repeated exposure to bright sunlight has an increasingly
adverse effect on dark adaptation. This effect is intensified by reflective
surfaces such as sand and snow. Exposure to intense sunlight for two to
five hours decreases scotopic visual sensitivity for as long as five hours.
Also, a decrease occurs in the rate of dark adaptation and degree of night
visual capacity. These effects are cumulative and may persist for several
days. If a night flight is scheduled, crew members should wear military
neutral density (N-15) sunglasses or equivalent filter lenses when exposed
to bright sunlight. This precaution will increase the rate of dark adaptation
at night and improve night visual sensitivity.
(2) Oxygen supply. Unaided night vision depends on optimum function
and sensitivity of the rods of the retina. Lack of oxygen to the rods
(hypoxia) significantly reduces their sensitivity. This increases the time
required for dark adaptation and decreases the ability to see at night.
Without supplemental oxygen, an individual's night vision declines
measurably at pressure altitudes above 4,000 feet. Because I2 device
output is photopic and central vision is the last to be degraded by a lack of
oxygen, aided night vision is not significantly affected. At night, aviators
should use oxygen, if available, when operating unaided above a pressure
altitude of 4,000 feet.
b. Precautions.
(1) Airfield lighting. At a fixed airfield, light sources that may impair the
aircrew's dark adaptation should be eliminated. Aircraft scheduled for
night flight should be positioned, if possible, on a part of the airfield
where the least amount of light exists. Maintenance and service crews
should practice light discipline. Hover lanes should be established and
marked with minimal appropriate lighting. This will preclude the use of
the landing light or searchlight during hover operations. Airfield lighting
should be reduced to the lowest intensity. The aviator should select
departure routes that avoid highways and residential areas where artificial
illumination can impair night vision. Runway and takeoff-pad lights, when
practical, should be reduced for departing traffic.
(2) High-intensity lighting. During night missions, aircrews may be
exposed to high-intensity lighting such as city lights, flares, searchlights,
lightning, and artillery flashes. These may cause a total or a partial loss of
night vision. If a flash of high-intensity light is expected from a specific
direction, the aviator should turn the aircraft away from the light source.
When such a condition occurs unexpectedly and direct view cannot be
avoided, a crew member can preserve his dark adaptation by shutting one
eye and using the other to observe. Once the light source is no longer
visible, the eye that was closed can provide the required night vision. This
is possible because dark adaptation occurs independently in each eye.
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However, it should be remembered that problems with depth perception
can occur when the aviator views with one dark-adapted eye. This is
particularly true when an aviator hovers near terrain obstacles or makes an
approach. Techniques to counter expected light conditions are discussed
below.
(a) Lights in built-up areas. The aviator should select flight routes
that avoid built-up areas which may have heavy concentrations of
light. If this condition is inadvertently encountered, the aviator
should alter the flight route to avoid overflying the brightly lit area.
A decrease in dark adaptation from a single light source, such as a
farmhouse or an automobile, can be minimized by looking away
from the light.
(b) Flares. When a flare is used to illuminate the viewing area or is
inadvertently detonated nearby, the aviator should maneuver to a
position along the edge of the illuminated area. This procedure
reduces exposure to the light source.
(c) Weapon flashes. To reduce the effect of weapon flashes from
aerial weapon systems, the aviator should limit the time during
which the ordnance is expended. Rockets can be fired in almost
any combination without seriously impairing night vision. When
firing automatic weapons, the aviator should use short bursts of
fire. Closing an eye or looking away from the firing will also
minimize the loss of dark adaptation.
1-9. SELF-IMPOSED STRESS
Night flight is more fatiguing and stressful than day flight. Many self- imposed stressors
limit night vision. Crew members can control this type of stress. The factors that cause
self-imposed stress are discussed below; crew members can remember them by the
acronym DEATH.
a. Drugs. Drugs can seriously degrade visual acuity during the day and especially
at night. A crew member who becomes ill should consult a flight surgeon.
b. Exhaustion. If crew members become fatigued during a night flight, they will
not be mentally alert. Exhaustion causes crew members to respond more slowly,
even in situations requiring immediate reaction. Exhausted crew members tend to
concentrate on one aspect of a situation without considering the total requirement.
Their performance may become a safety hazard, depending on the degree of
fatigue. Rather than use proper scanning techniques, they are prone to stare.
(1) Illness. Increased temperature and a feeling of unpleasantness usually
are associated with illness. High body temperatures consume a higher than
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normal rate of oxygen. As a result, hypoxia may be induced and night
vision may be degraded. In addition, the unpleasant feeling associated
with sickness distracts a crew member's attention and degrades his ability
to concentrate on night flying requirements.
(2) Poor physical conditioning. To overcome this limitation, crew
members should participate in regular exercise programs. Crew members
who are physically fit become less fatigued during flight and have better
night scanning efficiency. However, too much exercise in a given day may
leave crew members too fatigued for night flying.
(3) Inadequate rest. Adequate rest and sleep are important before flying.
Commanders should refer to the crew endurance scheduling guide in AR
95-1 when developing crew work and rest schedules.
c. Alcohol. Alcohol is a sedative. Its use impairs both coordination and judgment.
As a result, crew members impaired by alcohol fail to apply the proper techniques
of night vision. They are likely to stare at objects and to neglect scanning
techniques. The amount of alcohol consumed determines the degree to which
night vision is affected. The effects of alcohol are long-lasting; hangovers also
impair visual scanning efficiency.
d. Tobacco. Of all the self-imposed stressors, cigarette smoking most decreases
visual sensitivity at night. Smoking significantly increases the amount of carbon
monoxide carried by the hemoglobin in red blood cells. This reduces the blood's
capacity to combine with oxygen so less oxygen is carried in the blood. Hypoxia
caused by carbon monoxide poisoning affects peripheral vision and dark
adaptation. The results are the same as those for hypoxia caused by high altitude.
Smoking 3 cigarettes in rapid succession or 20 to 30 cigarettes within a 24-hour
period may saturate from 8 to 10 percent of the capacity of hemoglobin. Smokers
lose 20 percent of their night vision capability at sea level. This equals a
physiological altitude of 5,000 feet.
e. Hypoglycemia and Nutritional Deficiency.
(1) Hypoglycemia. Missing or postponing meals can cause low blood
sugar, which impairs night flight performance. Low blood sugar levels
may result in stomach contractions, distraction, a breakdown in habit
pattern, a shortened attention span, and other physiological changes.
(2) Vitamin A deficiency. Insufficient consumption of vitamin A may
impair night vision. Foods high in vitamin A include eggs, butter, cheese,
liver, apricots, peaches, carrots, squash, spinach, peas, and most types of
greens. A balanced diet usually provides enough vitamin A. Excessive
quantities of vitamin A will not improve night vision and may be harmful.
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1-10. SCANNING TECHNIQUES
Dark adaptation is only the first step toward increasing aircrews' ability to see at night.
Applying night vision techniques will enable aircrews to overcome many of the
physiological limitations of their eyes. Because the fovea centralis is automatically
directed toward an object by a visual fixation reflex, scanning techniques require
considerable practice and concerted effort on the part of the viewer.
a. Scanning. Scanning techniques are important in identifying objects at night. To
scan effectively, crew members look from right to left or left to right. They should
begin scanning at the greatest distance an object can be perceived (top) and move
inward toward the position of the aircraft (bottom). This scanning pattern is
shown in Figure 1-6. Because the light-sensitive elements of the retina cannot
perceive images that are in motion, a stop-turn-stop-turn motion should be used.
For each stop, an area approximately 30 wide should be scanned. This viewing
angle will include an area approximately 250 meters wide at a distance of 500
meters. The duration of each stop is based on the degree of detail that is required,
but no stop should last longer than two to three seconds. When moving from one
viewing point to the next, crew members should overlap the previous field of
view by 10 . Other scanning techniques, such as the ones illustrated in Figure 1-7,
may be used if appropriate to the situation.
Figure 1-6. Scanning pattern
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Figure 1-7. Alternate scanning pattern
b. Off-Center Viewing.
(1) Viewing an object using central vision during daylight poses no
limitation. If this same technique is used at night, however, the object may
not be seen because of the night blind spot that exists during low
illumination. To compensate for this limitation, crew members must use
off-center vision. This technique requires that an object be viewed by
looking 10 above, below, or to either side of the object. In this manner, the
peripheral vision can maintain contact with an object. Figure 1-8
illustrates an example of the off-center viewing technique.
(2) The technique of off-center vision applies only to the surveillance of
targets that are minimally illuminated or luminous. Under these
conditions, cone vision is not stimulated. Central vision is best used when
an object or a target is bright enough to stimulate the cones and needs to
be seen with considerable detail. When the object or target begins to fade,
it should be redetected using off-center vision and retained until central
vision recovers sufficiently to permit further observation.
(3) With off-center vision, the images of an object viewed longer than two
to three seconds will disappear. This occurs because the rods reach a
photochemical equilibrium that prevents any further response until the
scene changes. This produces a potentially unsafe operating condition. To
overcome this night vision limitation, crew members must be aware of the
phenomenon and avoid viewing an object for longer than two or three
seconds. The peripheral field of vision will continue to pick up the object
when the eyes are shifted from one off-center point to another.
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Figure 1-8. Off-center viewing technique
1-11. DISTANCE ESTIMATION AND DEPTH PERCEPTION
Distance estimation and depth perception cues are easily recognized when crew members
use central vision under good illumination. As the light level decreases, the ability to
judge distances accurately is degraded and visual illusions become more common. A
knowledge of distance estimation and depth perception mechanisms and cues will assist
crew members in judging distances at night. These cues may be monocular or binocular.
Monocular cues are more important for crew members than binocular cues.
a. Monocular Cues. The monocular cues that aid in distance estimation and depth
perception include motion parallax, geometric perspective, retinal image size, and
aerial perspective.
(1) Motion parallax. This cue to depth perception is a means of judging
distances under reduced illumination. Motion parallax refers to the
apparent motion of stationary objects as viewed by an observer moving
across the landscape. When the crew member looks outside the aircraft,
perpendicular to the direction of travel, near objects appear to move
backward, past, or opposite the path of motion. Far objects seem to move
in the direction of motion or remain fixed. The rate of apparent movement
depends on the distance the observer is from the object. For example, as
an aviator flies low level, objects near the aircraft will appear to rush past
the aircraft while a mountain range near the horizon will appear stationary.
As the aviator flies across a power line that extends to the horizon, that
part of the power line near the aircraft will appear to move swiftly,
opposite the path of motion. Toward the horizon, the same power line will
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appear fixed. Objects that appear to be fixed or moving slowly are judged
to be a greater distance from the aviator than objects that appear to be
moving swiftly.
(2) Geometric perspective. An object may appear to have a different shape
when viewed at varying distances and from different angles. Geometric
perspective cues include linear perspective, apparent foreshortening, and
vertical position in the field. They are illustrated in Figure 1-9.
(a) Linear perspective. Parallel lines, such as runway lights, tend to
converge as distance from the observer increases. This is illustrated
in part A of Figure 1-9.
(b) Apparent foreshortening. The true shape of an object or a
terrain feature appears elliptical when viewed from a distance. As
the distance to the object or the terrain feature decreases, the
apparent perspective changes to its true shape or form. Part B of
Figure 1-9 illustrates how the shape of a body of water changes
when viewed at different distances at the same altitude.
(c) Vertical position in the field. Objects or terrain features farther
away from the observer appear higher on the horizon than those
closer to the observer. The higher vehicle in part C of Figure 1-9
appears to be closer to the top and, thus, at the greater distance
from the observer. At night, crew members can mistake lights on
elevated structures or lights on low-flying aircraft for distant
ground structures because of the lights' higher vertical position in
the field.
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Figure 1-9. Geometric perspective
(3) Retinal image size. The brain perceives the actual size of an object
from the size of an image focused on the retina. Four factors are
considered in determining distance using the retinal image. They are
known size of objects, increasing or decreasing size of objects, terrestrial
associations, and overlapping contours or interposition of objects.
(a) Known size of objects. The nearer an object is to the observer,
the larger its retinal image. By experience, the brain learns to
estimate the distance of familiar objects by the size of their retinal
images. Figure 1-10 shows how this process works. A structure
projects a specific angle on the retina based on its distance from
the observer. If the angle is small, the observer judges the structure
to be at a great distance. A larger angle indicates to the observer
that the structure is close. To use this cue, the observer must know
the actual size of the object. If the observer is not familiar with the
object, its distance would be determined primarily by motion
parallax.
Figure 1-10. Known size of objects
(b) Increasing or decreasing size of objects. If the retinal image
size of an object increases, the relative distance is decreasing. If
the image size decreases, the relative distance is increasing. If the
image size is constant, the object is at a fixed relative distance.
(c) Terrestrial associations. Comparing an object, such as an
airfield, with an object of known size, such as a helicopter, helps to
deter- mine the object's size and apparent distance from the
observer. Objects ordinarily associated together are judged to be at
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about the same distance. For example, a helicopter observed near
an airport is judged to be in the traffic pattern and, therefore, at
about the same distance as the airfield. Figure 1-11 illustrates
terrestrial association.
Figure 1-11. Terrestrial association
(d) Overlapping contours or interposition of objects. When objects
overlap, the overlapped object is farther away, as illustrated in
Figure 1-12. This overlapping is especially important to consider at
night during a landing approach. Lights disappearing or flickering
in the landing area indicate barriers between the landing area and
the aircraft. The flight path should be adjusted accordingly.
Figure 1-12. Overlapping contour
(4) Aerial perspective. The clarity of an object and the shadow cast by it
are perceived by the brain and are cues for estimating distance. Several
aerial perspective factors are used to determine distance.
(a) Variations in color or shade. Subtle variations in color or shade
are clearer the closer the observer is to an object. However, as
distance increases, these distinctions blur. For example, the side of
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a hill from a distance will appear to be a uniform shade with no
distinguishable shape. As the aircrew flies closer to the hill, the
shades produced by individual trees and the spaces in between
those trees become noticeable. Thus under high light levels at
night, color or shade can provide cues for distance estimation.
(b) Loss of detail or texture. As a person gets farther from an
object, discrete details become less apparent. For example, when a
cornfield becomes a solid color and the leaves and branches of a
tree become a solid mass, the objects are judged to be far away.
Because reduced illumination also decreases resolution, these cues
will disappear shortly after sunset or be limited to close viewing
distances.
(c) Position of light source and direction of shadow. Every object
will cast a shadow from a light source. The direction in which the
shadow is cast depends on the position of the light source. If the
shadow of an object is toward the observer, the object is closer
than the light source is to the observer. Figure 1-13 illustrates light
and shadows.
Figure 1-13. Light and shadows
b. Binocular Cues. Binocular cues depend on the slightly different view each eye
has of an object. Consequently, binocular perception is useful only when the
object is close enough to make an obvious difference in the viewing angle of both
eyes. In the flight environment, most distances outside the cockpit are so great
that binocular cues are of little, if any, value. In addition, binocular cues operate
on a more subconscious level than monocular cues and are performed
automatically.
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1-12. VISUAL ILLUSIONS
Decreasing visual information increases the probability of spatial disorientation. Reduced
visual references also create several illusions that can induce spatial disorientation. Many
types of visual illusions can occur in the aviation environment. Included among them are
autokinesis, ground light misinterpretation, relative motion, reversible perspective
illusion, false horizons, altered reference planes, and height perception illusion. Others
include flicker vertigo, fascination (fixation), structural illusions, and size-distance
illusion.
a. Autokinesis. When a static light is stared at in the dark, the light appears to
move, as shown in Figure 1-14. This phenomenon can be readily demonstrated by
staring at a lighted cigarette in a dark room. Apparent movement will begin in
about 8 to 10 seconds. Although the cause of autokinesis is not known, it appears
to be related to the loss of surrounding references that normally serve to stabilize
visual perceptions. This illusion can be eliminated or reduced by visual scanning,
by increasing the number of lights, or by varying the light intensity. The most
important of the three solutions is visual scanning. A light or lights should not be
stared at for more than 10 seconds. This illusion is not limited to light in darkness.
It can occur whenever a small, bright, still object is stared at against a dull dark or
nondescript background. Similarly, it can occur when a small, dark, still object is
viewed against a light, structureless environment. Anytime visual references are
not available, aircrews are subject to this illusion.
b. Ground Light Misinterpretation. A common occurrence is to confuse ground
lights with stars. When this happens, aviators unknowingly position aircraft in
unusual attitudes to keep the ground lights--believed to be stars--above them. For
example, some aviators have mistaken the lights along a seashore for the horizon
and have maneuvered their aircraft dangerously close to the sea; they believed
they were flying straight and level. Aviators have also confused certain geometric
patterns of ground lights. For example, aviators have identified moving trains as
landing zone lights and have been badly shaken by their near misses. To avoid
these problems, aviators should cross-check aircraft instruments. Also, position
lights of other aircraft in formation can be mistaken for ground lights and might
be lost against the horizon when another aircraft is at or below the altitude of the
observer. Figure 1-15 illustrates ground light and skylight illusion.
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Figure 1-14. Autokinetic illusion
Figure 1-15. Ground light and skylight illusion
c. Relative Motion. The illusion of relative motion can be illustrated by an
example. An aviator hovers an aircraft and waits for hover taxi instructions.
Another aircraft hovers alongside. As the other aircraft is picked up in the first
aviator's peripheral vision, the aviator senses movement in the opposite direction.
This illusion may be encountered during multihelicopter operations. Aircrews
may mistake the motion of another aircraft for that of their own. The only way to
correct for this illusion is to have sufficient experience to understand that such
illusions do occur and to not react to them on the controls. The use of proper
scanning techniques can help prevent this illusion.
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d. Reversible Perspective Illusion. At night, an aircraft may appear to be going
away when it is, in fact, approaching a second aircraft. This illusion often occurs
when an aircraft is flying parallel to another's course. To determine the direction
of flight, aircrews should observe aircraft lights and their relative position to the
horizon. If the intensity of the lights increases, the aircraft is approaching. If the
lights dim, the aircraft is moving away. Also, remembering the "3 Rs" will help
identify the direction of travel when other aircraft are encountered. If the red
aircraft position lights are on the right, the aircraft is returning (coming toward the
observer).
e. False Horizons. Cloud formations may be confused with the horizon or the
ground. Momentary confusion may result when the aviator looks up after having
given prolonged attention to a task in the cockpit. Because outside references for
attitude are less obvious and reliable at night, aviators should rely less on them
during night flight. Using instrument cross-checks can help prevent this situation.
While hovering over terrain that is not perfectly level, aviators might mistake the
sloped ground in front of the aircraft for the horizon and cause the aircraft to drift
while trying to maintain a stationary position. Figure 1-16 illustrates false horizon
illusion.
f. Altered Reference Planes. When approaching a line of mountains or clouds,
aviators may feel that they need to climb even though their altitude is adequate.
Also, when flying parallel to a line of clouds, aviators may tend to tilt the aircraft
away from the clouds.
g. Height Perception Illusion. When flying over desert, snow, water, or other
areas of poor contrast, crew members may experience the illusion of being higher
above the terrain than they actually are. This is due to the lack of visual
references. This illusion may be overcome by dropping an object, such as a
chemical light stick or flare, on the ground before landing. Another technique to
overcome this illusion is to monitor the shadows cast by near objects, such as the
landing gear, or skid shadows at a hover. Flight in an area where visibility is
restricted by haze, smoke, or fog produces the same illusion.
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Figure 1-16. False horizon illusion
h. Flicker Vertigo. Much time and research have been devoted to the study of
flicker vertigo. A light flickering at a rate between 4 and 20 cycles per second can
produce unpleasant and dangerous reactions. Such conditions as nausea, vomiting,
and vertigo may occur. On rare occasions, convulsions and unconsciousness may
also occur. Fatigue, frustration, and boredom tend to intensify these reactions.
During the day, the problem can be caused by sunlight flickering through rotor
blades or propellers. At night, it can also be caused by an anticollision light
reflecting against an overcast sky, haze, or the rotor system. This can be corrected
by turning the anticollision light off.
i. Fascination (Fixation). This illusion occurs when aviators ignore orientation
cues and fix their attention on a goal or an object. This is dangerous because
aircraft ground-closure rates are difficult to determine at night; normal daylight
peripheral movement is reduced or absent. Target hypnosis is a common type of
fascination. For example, an aviator intent on hitting a target during a gunnery run
may delay pull-up so long that the aircraft contacts the ground. Preventing this
illusion requires increased scanning by the aviator.
j. Structural Illusions. Structural illusions are caused by heat waves, rain, snow,
sleet, or other factors that obscure vision. For example, a straight line may appear
to be curved when seen through a desert heat wave or a wing-tip light may appear
to double or move when viewed during a rain shower.
k. Size-Distance Illusion. This illusion results from viewing a source of light that
is increasing or decreasing in luminance (brightness). The aviator may interpret
the light as approaching or retreating. For example, when an aviator, hovering
near a second aircraft, changes the position lights from DIM to BRIGHT, the
other aircraft may appear to jump toward him.
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1-13. AIRCRAFT DESIGN LIMITATIONS
The design of Army aircraft may degrade a crew member's ability to see outside the
aircraft. To minimize the loss of night vision because of aircraft design shortcomings, an
aircrew must properly prepare the aircraft for night flight. Consideration should be given
to the aircraft limitations discussed below.
a. Windscreens reduce the ability to see outside the aircraft. Dirt, grease, and bugs
must be removed from the windscreen before each night flight.
b. Aircraft instruments are easier to read under high levels of instrument
illumination. However, the level of illumination needed for optimum reading
interferes with maximum dark adaptation for viewing dim objects outside the
aircraft.
c. Interior lights also interfere with dark adaptation. They reflect off the
windscreen and reduce outside visibility. Also, interior lights may be detected by
the Threat. To reduce the adverse effects of cockpit lights, the aviator should turn
off nonessential lights and keep the intensity of essential lights at the lowest
usable level.
d. Exterior lights are used to identify the aircraft. During aided terrain flight, the
illumination from these lights may degrade the operation of the I2 system. To
reduce the adverse effect of exterior lights, the aviator should turn off all lights
not required by regulations. The remaining lights should be operated in the DIM
mode or properly taped or painted.
1-14. NERVE AGENTS AND NIGHT VISION (MIOSIS)
Night vision is adversely affected when eyes are exposed to minute amounts of nerve
agents. When direct contact occurs, the pupils constrict (miosis) and do not dilate in low
ambient light. The available automatic chemical alarms are not sensitive enough to detect
the low concentrations of nerve agent vapor that can cause miosis.
a. Exposure Time. The exposure time required to cause miosis depends on the
concentration of the agent. Miosis may occur gradually as eyes are exposed to low
concentrations over a long period of time. On the other hand, exposure to a high
concentration can cause miosis during the few seconds it takes to put on a
protective mask. Repeated exposures over a period of days are cumulative.
b. Symptoms.
(1) The symptoms of miosis range from minimal to severe, depending on
the dosage to the eye. Severe miosis, with the resulting reduced ability to
see in low ambient light, persists for about 48 hours after onset. The pupil
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gradually returns to normal over several days. Full recovery may take up
to 20 days. Repeated exposures within the affected time are cumulative.
(2) The onset of miosis is insidious because it is not always immediately
painful. Miotic persons may not realize their condition even when they
carry out tasks that require vision in low ambient light. If the unit is
attacked by nerve agents, especially the more persistent types,
commanders should assume that personnel otherwise fit for duty will
experience some loss of night vision. No effective drug is available to
remedy the effects of miosis without causing other visual problems that
may be just as severe.
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CHAPTER 2
AVIATION NIGHT VISION DEVICES
The two types of aviation night vision devices are image-intensifier systems and thermalimaging systems. I2 systems amplify both visible and near infrared light energy. They
greatly improve night vision, but they require some degree of light to function. I2 systems
also do not work well under very low ambient light and adverse weather conditions. The
most recent advance in night vision devices is thermal imaging, which detects infrared
energy. Thermal-imaging systems detect heat radiated by objects and do not need light to
function. They are less affected by weather conditions than I2 systems. Thus far, only the
AH-64 has a thermal-imaging pilotage system, the PNVS. Appendix A discusses the
portions of the electromagnetic spectrum that are sensed by image-intensifier systems and
thermal-imaging systems.
Section I IMAGE-INTENSIFIER SYSTEMS
2-1. DEVELOPMENT HISTORY
a. A type of goggles for aviators to use during night helicopter operations was
first demonstrated in 1969. Because Army tactical doctrine at that time did not
require low-level or NOE night flight, I2 system development stopped. In 1971,
however, the Army reevaluated tactical helicopter employment and determined
that NOE operations were necessary at night as well as during the day. As a
result, the AN/PVS-5 was adopted as an interim pilot's night vision system
because it was a significant improvement over unaided night vision.
b. The AN/PVS-5 series contains second-generation image-intensifier tubes. As
use of the AN/PVS-5 expanded, the major limitation of the full faceplate--lack of
peripheral vision--became apparent. Subsequently, the faceplate was modified
(cut away) to provide peripheral vision. The AN/AVS-6 was developed to
overcome or reduce the limitations of the AN/PVS-5 series. The AN/AVS-6 uses
third-generation image-intensifier tubes to increase light amplification
approximately two times more than the AN/PVS-5 series. The AN/AVS-6 also
increases peripheral vision and has a flip-up feature. Both the AN/PVS-5 series
and the AN/AVS-6 are being used. Figure 2-1 shows a comparison of peripheral
vision for the various models.
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Figure 2-1. Peripheral vision comparison of various I2 models
2-2. OPERATIONAL THEORY
An image intensifier is an electronic device that amplifies light energy. The light enters
into the I2 device and is focused by the objective lens onto a photocathode that is
receptive to both visible and near infrared radiation. Figure 2-2 illustrates the operation of
an I2 device. The photons of light striking the photocathode cause a release of electrons
proportionate in number to the amount of light projected through the lens. In turn, the
released electrons are accelerated away from the photocathode surface by an electrical
field that is produced by the device's power source. The amount of light produced by the
I2 tube is proportional to both the number and the velocity of electrons that strike the
phosphor screen. The number of electrons striking the phosphor screen is increased by
means of the microchannel plate, which is a thin wafer of tiny glass tubes. The glass
tubes are tilted in the microchannel plate approximately 8 . Electrons enter these tubes
and strike the walls of the tubes. As each electron strikes a wall, more electrons are
emitted. Each of these emitted electrons strikes the wall again, producing even more
electrons. The accelerated electrons are directed through the microchannel plate and
against a phosphor screen placed on a flat plate opposite and parallel to the photocathode
surface. The phosphor screen emits an amount of light proportional to the number and
velocity of the electrons that strike it. Voltage is applied between the photocathode and
the phosphor screen. This accelerates the electrons, "brightening" the projected scene.
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Thus the picture delivered to the user is converted from a small amount of light to
accelerated electrons and back to an amplified amount of light.
Figure 2-2. Image intensifier
2-3. AN/PVS-5 SERIES
a. Description.
(1) The AN/PVS-5 series is a self-contained, binocular image-intensifier
viewing system with no magnification. The device is passive in normal
operation. It measures about 6.5-inches square, weighs 30 ounces, and has
a 40 FOV. Power is supplied by a 2.7-volt DC mercury battery or a 3.0volt DC lithium battery or two 1.5-volt AA alkaline batteries. The device
operates satisfactorily between 2.5 volts and 3.4 volts. The full-faceplate
version of the AN/PVS-5 completely surrounds the wearer's eyes. Only
through-the-tube viewing is possible, and eyeglasses cannot be worn.
Under ideal conditions, visual acuity of 20/200 or less unaided can be
improved to 20/50 with the AN/PVS-5 series. Figure 2-3 shows the
AN/PVS-5 with full faceplate.
NOTE: Flying with full faceplate I2 systems is permitted only during the daytime with
daylight filters and with the second crew member unaided.
(2) The weight of I2 devices shifts the CG of the head and helmet system
forward. This out-of-balance condition can be relieved by attaching a
counterweight to the back of the helmet. Appendix B discusses I2 system
counterweights.
(3) The AN/PVS-5 series operates by intensifying ambient light 750 to
1,500 times. This is sufficient to provide good imagery under full
moonlight conditions down to marginal imagery during quarter moonlight
conditions. Below quarter moonlight conditions, artificial illumination
(usually infrared) may be required to light the helicopter's flight path.
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Figure 2-3. AN/PVS-5 series
b. Improvements and Modifications.
(1) AN/PVS-5A. This model has the same image intensifier as the
AN/PVS-5 but is constructed differently. The tubes are not
interchangeable. The ON-OFF switch on the AN/PVS-5A has a lift
requirement to turn on the infrared illuminator. All other features and parts
are the same.
(2) Modified faceplate. The faceplate of the AN/PVS-5A was modified for
aviation use by the US Army Aeromedical Research Laboratory. The MFP
was an interim quick-fix for the AN/PVS-5A to make it safer for crew
members to use. Figure 2-4 shows the AN/PVS-5A with the MFP.
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Figure 2-4. Modified faceplate, AN/PVS-5A
(a) The lower portion of the faceplate was removed and its
electrical components were relocated to the top. The MFP enables
the user to view around the goggles. This permits an aviator to
view the cockpit, read maps, and discern the color of aircraft and
ground lights. Eyeglasses may be worn with the MFP.
(b) The MFP is mounted between the front of the helmet and the
visor cover. It is held in place by the standard vee and side straps.
A side strap of surgical tubing can also be used.
(3) GX-5 flip-up modification. The GX-5 uses a pivoting hinge that locks
the device in a stowed position or lowers it for use. The hinge is hardmounted to a section of the visor cover and attached to the helmet visor
cover by Velcro. A new frame holds the I2 tubes and attaches to the lower
portion of the hinge by a bolt-and-nut assembly. This frame increases
peripheral unaided vision. The GX-5 flip-up modification requires the
dual-battery pack for power and ON-OFF switching. Figure 2-5 illustrates
the GX-5 flip-up modification.
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Figure 2-5. GX-5 flip-up modification, AN/PVS-5A
(4) AN/PVS-5B/C. The AN/PVS-5B/C uses the second-generation intensifier tube of the
AN/PVS-5A but with improved objective lenses that gather more light. This results in a
substantial improvement in low light flight capability. The AN/PVS-5B/C with the full
faceplate is not employed in Army aviation.
WARNING
The AN/PVS-5B/C is designed for ground use only
when the tube assemblies are in the original full
faceplate. A feature in the faceplate automatically cuts
off power if the tubes are exposed to continuous high
light levels for more than one minute. Aviation
personnel are not permitted to modify the AN/PVS5B/C faceplate.
c. Flight Helmet Attachment.
(1) A properly fitted flight helmet is essential for comfort and to lessen
fatigue. For the same reason, the flight helmet must be correctly modified
for attachment of the full-faceplate AN/PVS-5A, MFP, or GX-5
modification. Properly adjusted helmet headbands and nape straps will
help prevent the helmet from rotating forward and down during I2 device
use.
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(2) Helmet straps are supplied with each device. The aviation helmet kit
(vee straps and side straps) provides four attaching points (two male snaps
and two 2-inch Velcro strips) that must be attached to the helmet.
Instructions for preparing the helmet are described in TM 11-5855-238-10.
The SPH-4 helmet is not configured for external attachment of the
AN/PVS-5 series without modification.
2-4. AN/AVS-6
a. The AN/AVS-6 is a helmet-mounted, light-intensification device. Figure 2-6
shows the AN/AVS-6. The AN/AVS-6 allows aircrews to conduct operations at
terrain flight altitudes during low ambient light levels, to include overcast
conditions. It has the same 40 FOV as the AN/PVS-5 series. Under ideal
conditions, visual acuity of 20/200 or less can be improved to 20/40 with the
AN/AVS-6. Figure 2-7 illustrates the superiority of the AN/AVS-6 over the
AN/PVS-5 series because of its improved sensitivity in the red and near infrared
region of the spectrum. Light in this portion of the spectrum predominates at
night, as shown in Figure 2-8. Not only does the AN/AVS-6 provide greater light
amplification but it also amplifies light in that portion of the spectrum that is most
predominant at night.
NOTE: The small peak in the blue-green portion of the spectrum in Figure 2-8 is caused
by moon illumination. The size of this peak will vary based on the amount of moon
illumination.
b. The AN/AVS-6 operates by intensifying ambient light 2,000 to 3,500 times. It
can provide sufficient imagery from overcast starlight to moonlight conditions.
However, below quarter moonlight conditions, artificial illumination (usually
infrared) may be required to light the helicopter's flight path.
Figure 2-6. AN/AVS-6
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Figure 2-7. Relative sensitivity of AN/PVS-5 and AN/AVS-6 systems
Figure 2-8. Spectral distribution of starlight
c. The AN/AVS-6 comes in two versions: AN/AVS-6(V)1 and AN/AVS-6(V)2.
The AN/AVS-6(V)1 mounts directly to the standard SPH-4 flight helmet. A
special mount and offset binocular, the AN/AVS-6(V)2, is available for SPH-4
helmets modified with a helmet-mounted sight. The AN/AVS-6 is powered by
batteries or aircraft interface and has a 30-minute, low-voltage warning indicator.
The warning indicator is a dim red light emitted between the binoculars above the
FOV when 30 minutes or less of battery life remains.
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d. The AN/AVS-6 is stowable on the helmet in a flipped-up position, which
automatically cuts off power to the tubes. Figure 2-9 shows the AN/AVS-6 in the
stowed position. The AN/AVS-6 is significantly lighter than the AN/PVS-5 series
and has a breakaway feature designed to separate the binocular from the helmet
mount under crash loads. The AN/AVS-6 also has an improved unaided
peripheral view. It incorporates a minus-blue filter that makes the system
insensitive to blue-green cockpit lights and their reflections in the cockpit.
Figure 2-9. AN/AVS-6 in stowed position
2-5. ADJUSTMENT TECHNIQUES
a. Interpupillary Distance. If I2 device eyepieces are not properly aligned with the
eyes, less than optimum resolution with the device will be obtained. Proper
alignment of the eyepieces is achieved when the distance between the tubes
matches the distance between the user's pupils. When the interpupillary distance
of the I2 device is properly adjusted, the edges of the images in both tubes will be
clear. When the edges are clear, the resultant binocular view through the tubes
may appear as a single circle or as two circles. The circle or circles will be
overlapped and slightly displaced laterally. Interpupillary distance is adjusted
while the tubes are focused at infinity under dark-light conditions with all lens
caps removed. The procedure for adjusting interpupillary distance is described
below.
(1) Move the tubes away from the eyes as far as possible. This makes edge
clarity easier to judge.
(2) With both eyes open, move the tubes closer together and farther apart.
Observe the clarity of the edges of the circle in each eye. If the outside
edges are blurred, the tubes are too close together. If the inside edges are
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blurred, the tubes are too far apart. If the upper or lower edges are blurred,
tilt the tubes.
(3) Move the tubes closer to the eyes as desired without the eyelashes
touching the eyepiece lenses. Recheck the tube tilt.
b. Binocular Focus. Each I2 device has a method for dioptric adjustment. This
adjustment is used to correct visual refractive errors such as myopia
(nearsightedness) and hyperopia (farsightedness). For the AN/PVS-5 series, this is
accomplished with the diopter adjust ring. For the AN/AVS-6, it is accomplished
with the eyepiece focus ring. When setting the dioptric adjustment, the user may
achieve a clear image in each eye (monocular) and yet have a blurred image or
accommodative eyestrain when viewing with both eyes (binocular). This occurs
when the dioptric adjustment is set for one eye while the other eye is closed or
covered. In this situation, the eyes tend to accommodate to a nearer distance than
infinity, typically 1 to 3 feet. Over-accommodation or focus imbalance or both
between the eyes can cause eyestrain and periodic blurred vision. To achieve a
clear and relaxed binocular focus, the user should follow the procedure described
below after focusing the tubes for each eye and adjusting interpupillary distance.
(1) Focus at infinity and view a distant object.
(2) Slightly blur the image in one tube, left or right, with the focus knob
(AN/AVS-5 series) or objective focus ring (AN/AVS-6). The amount of
blur should allow recognition of general object shapes but not fine details
in the blurred tube.
(3) With both eyes open, adjust the diopter adjust ring or eyepiece focus
ring for the clearest image in the nonblurred tube.
(4) Return the blurred tube to infinity focus, blur the other tube, and repeat
the process.
2-6. OPERATIONAL CONSIDERATIONS
a. Magnification. I2 systems do not amplify an image. An object viewed through
an I2 system will be the same size as if it were seen with the unaided eye.
b. Lights.
(1) With an I2 device, individuals can detect light sources that may not be
visible to the unaided eye. Examples include lights from other aircraft,
flashlights, burning cigarettes, and chemical light sticks. As the ambient
light level decreases, aircrews can more easily detect these light sources
but are less able to estimate distance correctly.
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(2) Performance of I2 systems is directly related to the ambient light.
During periods of high ambient light, resolution is improved and objects
can be identified at greater distances, although not to the degree possible
during daylight. To light the flight path of a helicopter in low ambient
light, the aviator may have to use an additional light source. Night scenes
viewed with I2 devices are shown in Figure 2-10.
(3) I2 devices are adversely affected by bright lights and periods of high
ambient light. When exposed to a bright light source, both the AN/AVS-6
and the AN/PVS-5 series are susceptible to whiteout. Saturation of the I2
system appears on the tube as a bright halo effect around the image of the
light source. The halo effect also degrades the contrast of adjacent portions
of the intensified image. This degradation of performance becomes worse
when several bright lights appear in the field of view. Additionally,
internal circuitry automatically adjusts output brightness to a preset level
to restrict peak display luminance. When an area with bright lights is
viewed, the display luminance will decrease ("shut down"). In addition to
the halo effect around a bright light source, the overall display luminance
of the rest of the viewed scene will dim. The brighter the light source, the
dimmer the rest of the viewed scene. The crew member may also
experience the dimming effect when viewing in the direction of a full
moon at low angles above the horizon.
(4) Tunnel vision limits an individual's ability to see outside an area lit by
bright artificial lights such as flares, landing lights, and lights with infrared
filters. The ability to see objects within the lighted area depends on the
intensity of the light and the distance of the object from the viewer. A
crew member should not look directly at a bright light source because it
may temporarily degrade the efficiency of the I2 system. When flying with
the landing light or searchlight with the pink light filter or infrared bandpass filter on, the aircrew should avoid concentrating on the area
illuminated by the light. The aircrew should also scan the area not
illuminated by the light for hazards and obstacles.
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Figure 2-10. Night scenes viewed with I2 devices
c. Depth Perception and Distance Estimation. Depth perception and distance
estimation are difficult with I2 systems. The quality of an individual's depth
perception in a given situation depends on several factors. They include the
available light, type and quality of the I2 system used, degree of contrast in the
field of view, and viewer's experience. The aircrew must rely on the monocular
cues discussed in Chapter 1 for accurate depth perception and distance estimation.
d. Color Discrimination. Color discrimination is absent when scenes are viewed
through I2 systems. The picture seen with I2 systems is monochromatic (single
color). It has a green hue because of the type of phosphor used on the phosphor
screen of the I2 tube. The green hue in I2 systems may cause crew members to
experience a pink, brown, or purple afterimage when they remove the device.
This is called chromatic adaption and is a normal physiological phenomenon. The
length of time the afterimage remains varies with the individual.
e. Scanning Techniques. Although the basic principles of scanning are the same
for unaided and aided flight, crew members must consider a few specific items
when conducting operations with I2 devices. Flight techniques and visual cues for
unaided night flight also apply to aided night flight. Use of the I2 device improves
ground reference but significantly reduces the field of view.
(1) The FOV of I2 devices significantly reduces peripheral vision as
compared with unaided flight. Thus the crew member must use a continual
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scanning pattern to compensate for the loss. Moving the eyes will not
change the viewing perspective; the head must be turned. However, rapid
head movement can induce spatial disorientation. To view an area while
using an I2 device, the crew member must rotate his head and eyes slowly
and continuously. When scanning to the right, he should move his eyes
slowly from the left limit of vision inside the device to the right limit
while moving his head to the right. In this manner, the crew member will
cover a 70 to 80 viewing field with only 30 or 40 of head movement. This
technique minimizes head rotation. However, maximum visual acuity can
only be attained when the crew member views through the center of the
tube. Acuity drops to 20/70 or worse in the periphery of the I2 device
FOV. The crew member should scan back to the left in reverse order and
avoid rapid head movements because they can induce vertigo. The crew
member must develop scanning techniques that involve a mix of unaided
and aided vision.
(2) The devices provide the primary source for detailed visual information.
When viewed through the devices, illumination sources, such as aircraft
position lights and ground lights, may not be accurately interpreted
according to intensity, distance, or color. Unaided vision can provide this
additional information. With the newly modified I2 device-compatible
aircraft cockpits, a slight downward deflection of the eyes will provide all
required visual information inside the cockpit.
(3) Practice and experience are necessary to obtain maximum visual
information from both unaided and aided vision. Initially, unaided
peripheral vision may be somewhat distracting until the crew member
develops adequate experience combining through-the-tube viewing with
around-the-device scanning.
NOTE: Continuous flight with one lens focused inside and one focused outside the
aircraft is prohibited. This can cause spatial disorientation, headaches, eyestrain, and
reduced visual acuity.
f. Obstruction Detection. Obstructions that have poor reflective surfaces, such as
wires and small tree limbs, are difficult to detect. The best way to locate wires is
to look for the support structures. Hazardous wires in high-use areas should be
marked with reflective devices.
g. Spatial Disorientation. Maneuvers requiring large bank angles or rapid attitude
changes tend to induce spatial disorientation. Therefore, the aviator should avoid
making drastic changes in attitude and bank angle and use proper scanning and
viewing techniques.
h. Airspeed and Ground Speed Limitations. Aviators using I2 devices tend to
overfly their capability to see. To avoid obstacles, they must understand the
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relationship between the device's visual range and forward lighting capability and
airspeed.
WARNING
The visual range of the I2 devices may not allow aviators enough time to
avoid obstacles. Therefore, aviators must exercise extreme care when
using the devices during terrain flight modes. Aviators should reduce
ground speed so that they can detect and avoid obstacles when ambient
light levels are low or visibility is poor because of weather conditions.
(1) Different light levels affect the distance at which crew members can
identify an object. This, in turn, limits the ground speed at which aviators
can safely fly at terrain flight altitudes. Ground speed limitations are not
quantified because of continuously changing variables affecting the
limitations. Variables include the type of aircraft, type and quality of I2
device, supplemental lighting, vision obscurations, and ambient light
conditions.
(2) Object acquisition and identification are related to ambient light levels,
visibility, and contrast between the object and its background. For safety
reasons, light levels required for training may differ considerably from
operational requirements. Variables that affect the ability to see with I2
devices include-o
o
o
o
o
o
o
o
Type of I2 device.
Condition of aircraft windscreen.
Age and condition of tubes and lenses.
Moisture content in the air (humidity).
Individual's proficiency and capabilities.
Proper care and maintenance of the I2 device.
Capabilities of infrared band-pass filter used.
Visibility (haze, fog, rain, low clouds, dust, smoke).
i. Aircraft Lighting. Various sources of lighting (especially red) that are not
compatible with I2 systems may degrade the aviator's ability to see with the
system. The adverse effects of aircraft lighting on the I2 device are greatest during
low ambient light conditions.
(1) Cockpit lights. The initial I2 cockpit lighting used with the fullfaceplate AN/PVS-5 series was an "infrared cockpit illuminator." It was a
modified map light that flooded the blacked-out instrument panel with a
dim infrared light. The instrument panel was readable when an I2 tube was
focused inside. Indicator, caution, and warning lights were dimmed to an
acceptable I2 level by covering them with tape. Night-Fix, Phase I,
employed blue-green lighting that had a negligible effect on I2 devices.
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Blue-green filters pass only blue-green light and block all other light,
especially red and infrared. All red lighting was extinguished by an ONOFF NVG light switch that activated the blue-green lights flooding the
instrument panel. Indicator, caution, and warning lights were dimmed by
blue-green filters. This system was designed for compatibility with the
AN/AVS-6 and is therefore only partially compatible with the AN/PVS-5
series. Night-fix, Phase II, employed the same blue-green filters, but each
instrument, radio, panel, and indicator light was illuminated or dimmed
individually. All red lighting was removed. Suggested ways to improve I2
cockpit lighting are discussed on the next page.
(a) AN/PVS-5 series. The blue-green lighting should be dimmed to
the lowest readable level based on the ambient light level and the
aviator's dark adaptation level. This is required because the
AN/PVS-5 series is sensitive to all colors of light. Dimming them
reduces reflections on the windscreen, which limit I2 performance.
The AN/PVS-5 series does not have the minus-blue filter like that
used on the AN/AVS-6.
(b) AN/AVS-6. The AN/AVS-6 is designed to be operated with
blue-green cockpit lights. The combination of improved
performance in the red and near infrared portion of the spectrum
and the minus-blue filter makes red cockpit lights noncompatible
and blue-green cockpit lighting ideal. The use of red cockpit
lighting should be avoided or strictly limited. While the use of
blue-green cockpit lights will not degrade system performance,
these lights should be dimmed to the lowest readable level.
(c) Both systems. Light reflected on the windscreen of the aircraft
may degrade the aircrew's ability to see outside the cockpit.
Aircraft lights that cannot be controlled should be covered with a
filter compatible with I2 devices or with a light-reducing material
such as tape. Flight instruments should be illuminated by interior
lighting compatible with I2 devices. The instruments can be read
by looking beneath the I2 device.
(2) Supplemental external lights. During Night-Fix, Phase I, a pink light
filter was mounted on the standard landing light. It provides supple-mental
infrared lighting, useful for 100 to 200 feet, which can be directed forward
in the helicopter's flight path to detect obstacles. Figure 2-11 shows the
pink light. The speed of the helicopter is reduced based on the range of the
light and visibility restrictions. Further aircraft modification includes an
improved infrared band-pass filter mounted on the searchlight or landing
light. Different bulbs can vary the distance and beam spread of the
infrared light path. Figure 2-12 shows the infrared band-pass filter in
place.
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Figure 2-11. Pink light
Figure 2-12. Infrared band-pass filter
(3) External lights. I2 flights are degraded by aircraft external lights unless
they are properly modified. The lights should be adjusted to the lowest
level that will still allow detection by other aircraft or the control tower.
The top half of the lower navigation lights and bottom half of the top
navigation lights should be painted or taped to allow aviators to see
through an unlit area surrounding the cockpit.
(a) Red navigation lights on the left side of the helicopter produce
more usable light with I2 systems than green lights. In unaided
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flight, the opposite is true. Aviators switching seats should
anticipate this, especially during hovering. Other lights--fuselage,
formation, anticollision, electroluminescent panels (slime lights),
and infrared position lights--should be turned off or subdued.
Otherwise, their use should be based on training, tactical, or
airspace requirements. Figure 2-13 shows the front of a UH-1
helicopter viewed through an I2 device. The red light on the left
side of the helicopter appears much brighter than the green light on
the right side.
(b) External aircraft lights aid the aircrew in interpreting terrain
close to the aircraft. To minimize the adverse effects of external
lights on night vision, the aviator should operate navigation lights
in the DIM position when they are required. The anticollision light
can be turned off to enhance training. The pink light filter or
infrared band-pass filter should be used for training during periods
of low ambient light. Exterior lights of other aircraft will not
degrade the vision of an aircrew using I2 systems if the lights are
taped and operated properly.
Figure 2-13. Effect of position lights on I2 devices
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j. Weather. When using I2 systems, aviators may fail to detect entry into IMC.
This is because the I2 systems may enable aviators to see through obscurations
such as fog, rain, haze, dust, and certain types of smoke.
(1) As the density of the visibility restriction increases, aircrews will
detect a gradual reduction in light and visual acuity. When they recognize
that their visibility is restricted, they should try to determine the severity
of the condition and take appropriate action. This may include reducing
airspeed, increasing altitude, seeking areas of contrast, or landing. If visual
flight cannot be maintained, aviators should execute the appropriate IMC
recovery procedures.
(2) Certain visual cues will be evident when visibility restrictions are
encountered. A halo may form around sources of illumination when
devices are used and atmospheric obscurations are present. The size of this
halo effect around lights in the area of operations should be noted. If the
halo becomes noticeably larger, a restriction could be developing. Also, an
increase in "image noise" may result when atmospheric obscurations are
present and the ambient light level is low. This is similar in appearance to
the "snow" seen on a television with poor reception.
k. Weapons.
(1) Tube-launched, optically tracked, wire-guided missiles. TOW missile
engagements at night should be made with unaided vision and with the
appropriate artificial illumination for target acquisition. During TOW
missile engagements, aviators may encounter conditions that adversely
affect the use of the I2 device. The most critical of these conditions are
listed below.
•
•
•
Initially, the target will not be visible because of the light intensity produced by
the missile's flight motor.
The aviator's ability to see the target will be impaired by the missile's infrared
source as the missile continues downrange.
Damage may occur to the lens of the telescopic sighting unit.
(2) Rockets, cannons, and machine guns. When firing the 2.75-inch
folding-fin aerial rocket, aviators will lose sight of the target momentarily.
After the rocket leaves the launcher, they will immediately regain sight of
the target. Firing the 20-millimeter cannon can cause some visual
impairment. Firing the 7.62-millimeter machine gun will cause loss of
sight with the target during the entire firing burst.
NOTE: Recovery from bright flash illumination is more rapid with I2 devices than with
the unaided eye.
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Section II
THERMAL-IMAGING SYSTEMS
2-7. OPERATIONAL PRINCIPLES
a. Operation of thermal-imaging systems differs from that of I2 systems. Thermal
systems operate passively and without regard to levels of visible light. These
systems do not transmit energy. Rather, they sense and display the energy radiated
from objects. Thermal-imaging systems provide aviators with an image of an
infrared scene. This enables aviators to operate in environments that could restrict
or prohibit unaided operations.
b. The effectiveness of a thermal-imaging system depends on the difference in
detected infrared radiation between the object to be detected and its background.
Effectiveness also depends on atmospheric considerations--the degree of
obscuration present between the system and the object. Thermal systems are most
effective when a great difference in infrared radiation exists between an object
and its background and when obscuration is minimal.
2-8. SYSTEM TYPES
Four types of thermal devices are currently used on Army aircraft. The PNVS, thus far, is
the only type of pilotage thermal system used. The other de-vices are target acquisition
systems. Aviators should consult the appropriate aircraft operator's manual for specific
operating instructions.
a. Pilotage System. The PNVS, which is mounted on the AH-64, is a type of
pilotage FLIR. Figure 2-14 illustrates the pilotage system. Appendix C provides a
detailed discussion of FLIR components.
b. Target Acquisition Systems. A brief description of target acquisition systems is
given below. An example of a target acquisition system, the TADS, is shown in
Figure 2-15.
(1) C-NITE sight. C-NITE is a thermal sight for firing TOW missiles from
the AH-1.
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Figure 2-14. Pilotage system
Figure 2-15. Target acquisition system
(2) Target acquisition and designation sight. The TADS is a day and night
sight and laser designator and range finder for the AH-64. The TADS
FLIR can be used as a backup to the PNVS.
(3) Mast-mounted sight. The MMS is a day and night sight and laser
designator and range finder for the OH-58D.
2-9. INFRARED CHARACTERISTICS
Infrared is measurable electromagnetic energy and is part of the electromagnetic
spectrum. The infrared region occurs beyond the visible light range. Infrared is, therefore,
invisible to the human eye.
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a. Infrared Radiation.
(1) A definition of reflectance, transmittance, absorptance, and emissivity
is given below.
(a) Reflectance--the ratio of radiant energy reflected by a body to
the radiant energy incident upon it.
(b) Transmittance--the ratio of radiant energy that, having entered
a body, reaches its farther boundary.
(c) Absorptance--the ratio of radiant energy absorbed by a body to
the radiant energy incident upon it.
(d) Emissivity--the relative power of a surface to emit heat
by radiation. It is the ratio of radiant energy emitted by a body--as
a consequence of its temperature only--to that emitted by a
reference body (blackbody) at the same temperature. This
additional characteristic has considerable significance regarding
object infrared radiation. A blackbody is a theoretical standard
used for the purpose of laboratory comparison. It is an ideal body
or surface that completely absorbs all radiant energy falling upon it
with no reflection. A blackbody absorbs 100 percent of infrared
energy incident upon it and emits 100 percent of its infrared
energy. Therefore, a blackbody is both a perfect absorber and a
perfect emitter.
(2) Reflectance, transmittance, absorptance, and emissivity determine the
amount of infrared energy that an object will radiate when exposed to "x"
level of thermal energy for "x" amount of time. Incident infrared radiation
on a body may be reflected, transmitted through, and/or absorbed by the
body. Absorbed energy may be emitted over a period of time according to
the emissivity of the body. The total amount of infrared energy that an
object will radiate is the sum of reflected, transmitted, and emitted energy.
Figure 2-16 illustrates incident, reflected, absorbed, transmitted, and
emitted radiation.
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Figure 2-16. Infrared radiation
b. Minimum Resolvable Temperature. The FLIR can discriminate objects from
their respective backgrounds in the broad range of environmental conditions in
which the FLIR operates. FLIR performance is measured by determining the
MRT. A thermal-imaging system discriminates an object from its background by
measuring the difference between the total infrared radiation of the object and the
total infrared radiation of its background. MRT is de-fined as the lowest
equivalent thermal difference between an object and its background that can be
resolved, or seen, by an observer through a FLIR system. The lower the MRT, the
better the FLIR can discriminate an object from its background when the infrared
radiation characteristics are about equal at about equal temperatures.
c. Atmospheric Effects. Since 1979, the PNVS has been subjected to flight
operations in weather phenomena, including heavy rain, snow, sleet, fog, and
haze. These conditions were encountered in various types of terrain, including
deserts, mountains, and densely foliated swamps. These environments and
weather conditions were intentionally sought to determine the operational
capabilities of the PNVS. Data gathered during these environmental tests proved
that, in these conditions, the PNVS FLIR permits safe NOE flight operations most
of the time. As visibility was degraded, airspeed was reduced to avoid obstacles.
Figure 2-17 illustrates atmospheric effects on infrared radiation.
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Figure 2-17. Atmospheric effects on infrared radiation
(1) Atmospheric transmission. The term atmospheric transmission pertains
to signal reduction (attenuation) caused by the distance a signal travels
through a given air composition or density. Infrared signal attenuation is
directly proportional to changes in air composition or density. As moisture
in its various forms increases in the air, infrared signal strength is
attenuated.
(a) Condensing moisture forms clouds that may, in turn, form
heavy overcast conditions. The overcast conditions, especially if
they persist for several days, prevent most solar thermal radiation
from reaching the surface. This loss of thermal energy reduces
molecular activity in those substances beneath the overcast
conditions and subsequently reduces infrared radiation from those
substances.
(b) Heavy concentrations of moisture between a FLIR sensor and
the objects viewed tend to attenuate the infrared radiation from
those objects. These particles of moisture generate their own
molecular activity. In comparison, the radiation from these
particles is very small but may add to the overall interference in the
infrared signal transmission.
(c) Elements other than moisture also affect the composition or
density of the atmosphere and, therefore, affect infrared signal
transmission. Examples of these elements include dust, haze, and
smoke. FLIR penetration of these substances, as with moisture,
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depends on the size and amount of particulates between the sensor
and the objects viewed.
(2) FLIR performance. Where and in what intensity the conditions
described in (1) above may occur are relatively unpredictable. Therefore,
specific FLIR performance in specific environments cannot be defined
here. Given differentials in total radiation of objects relative to their
backgrounds, the image quality of the system will usually permit safe
terrain flight operations.
(a) The FLIR exceeds the capability of the human eye to operate in
visual obscurations or adverse weather conditions.
(b) The FLIR will usually "see" the obscuring condition before
penetration and will allow the aviator the option of
circumnavigation or penetration.
(c) The effect of atmospheric obscurations on thermal system
performance varies in direct proportion to the quantity and density
of the obscuration. It is also affected by the distance between the
sensor and the scene being viewed and the strength of the infrared
signatures of the objects in the scene. A scene viewed with the
FLIR is rarely obscured totally.
d. Infrared Energy Crossover.
(1) The final factor affecting infrared radiation is infrared energy
crossover. Figure 2-18 depicts a specific location and shows temperature
distributions of various substances during one 24-hour period. The effects
of solar thermal radiation can be seen by tracing any of the substance
curves from 0600 (assuming that is sunrise) to 1400.
(a) Figure 2-18, point A, depicts the time of day when soil, water,
and concrete cross over. In other words, the thermal radiation of
these substances nearly equalizes. The ability of a FLIR to
discriminate soil from concrete or water at that point would be
strictly a function of its MRT. The lower the MRT of the FLIR, the
less the system is affected by crossover and the less the time
interval that the system is affected.
(b) Figure 2-18, point B, depicts the time of day when the
temperature differences of these same substances are the greatest.
If this situation existed all the time, then the MRT of the FLIR
could be much higher and could still permit adequate scene
definition. However, the temperature differences depicted by point
B are generally more the exception than the rule.
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NOTE: This graph is an example only. Actual conditions will vary daily.
Figure 2-18. Infrared crossover
(2) As shown in Figure 2-18, crossover for soil, water, and concrete occurs
twice in 24 hours. Soil and concrete do not cross over with vegetation;
however, vegetation and water cross over twice in 24 hours. Figure 2-18
depicts conditions at one location on one day. The odds are against these
same plots recurring at that location on any other day. The effects of
weather (rain, fog, winds) can make even the same day quite different
from year to year. Geographically, terrain exhibits vastly different
temperatures over time. Crossover in the desert may occur several times in
one day and then not again for several days in a row.
(3) Predicting crossover is not an exact science. Infrared energy crossover
has the greatest impact on FLIR operations when it occurs simultaneously
with some atmospheric phenomenon such as haze or fog. The result is
poor image quality. Just how poor the quality is and how long it will
persist are relative variables that cannot be specifically defined. Therefore,
when using the system, an aviator must be prepared to encounter varying
atmospheric conditions. He must learn to contend with those conditions
through knowledge, understanding, and increasing operational
proficiency.
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2-10. OPERATIONAL CONSIDERATIONS
a. Lights. Lights visible to the unaided eye at night will not normally be visible
through the FLIR. Aviators can compensate for this by looking for lights with the
unaided eye.
b. Depth Perception and Distance Estimation. Depth perception and distance
estimation are greatly affected by the FLIR system. To help overcome the loss of
peripheral vision cues and the two-dimensional image, flight information is
symbolically superimposed on the FLIR image. The aviator must rely on flight
symbology and monocular cues for accurate depth perception and distance
estimation.
c. Color Discrimination. Color discrimination is absent when the aviator views
through the FLIR system. A green hue is seen similar to I2 devices as a result of
the phosphor used in the helmet-mounted display. The unaided eye, however, will
be able to distinguish the color of lights that are sufficiently bright for photopic
vision.
d. Parallax Effect. A parallax effect occurs in the PNVS because of the relative
distance between the FLIR sensor and the HDU. The FLIR sensor is contained
within the PNVS turret located on the nose of the aircraft. The HDU is positioned
in front of the pilot's eye. The PNVS turret is located approximately 10 feet
forward and 3 feet below the pilot's design-eye position. In both the pilot's station
and the CPG's station, the thermal scene viewed on the HDU is obtained from the
physical perspective point of the FLIR sensor.
(1) The aviator flying with the PNVS views with the FLIR sensor, not
with his unaided eye. Attempts to correlate the thermal scene viewed
through the HDU with the actual scene viewed with the unaided eye can
result in an apparent difference in the location of the objects within the
scene. In Figure 2-19, the aviator has turned his head 90 to the right. The
PNVS turret is also looking 90 to the right. An object (tree) is located at
"A" in the illustration. The FLIR sensor views the tree in the center of the
field of view along the LOS. The aviator's unaided eye, however, would
not see that same tree in the center of his FOV but rather would see the
tree slightly to the left of his LOS. The parallax effect increases with the
turret offset angle and the relative closeness of obstacles to the aircraft.
(2) The aviator must mentally transpose his view of the PNVS scene from
where he is seated to the PNVS turret where the view is obtained. This
mental exercise requires repetitive training and is required for effective
PNVS operation.
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Figure 2-19. Parallax effect
e. Binocular Rivalry. The term binocular rivalry is used to describe the
competition between the PNVS aided eye and the unaided eye while the aviator is
flying with the monocular-equipped PNVS. This rivalry can be described as an
undirected attention shift of the aviator's desired visual reference point (HDU
display) to an undesired point or scene or vice versa. The frequency and length of
these occurrences depend on several variables. These variables include HDU
luminance, ambient scene luminance, HDU scene complexity, ambient scene
complexity, and to a degree, eye dominance at early stages in training. Aviators
are accustomed to using both eyes simultaneously to perform flight duties. The
PNVS monocular display is positioned over and is used by only one eye (aided
eye) leaving the other eye unaided. The difficulty arises when the aviator is forced
to maintain a high degree of concentration while flying with the PNVS with only
the aided eye. At the same time, the aviator must manage the unaided eye so that
when it is attracted to a more dominant scene (for example, cockpit lights or
flares), an uncommanded shift of either eye can be prevented. Some ways the
aviator can control or prevent binocular rivalry are discussed below.
(1) The aviator should select one of the three cockpit lighting
configurations (floodlights bright, dim, or off) that works best for him. He
should try them all and select the one he prefers.
(2) During night flights, external light interferences are commonplace.
When practical, aviators should plan their flights to eliminate disturbances
from known light sources.
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(3) Dedicated concentration is required in managing visual perceptions
while using the PNVS. Even the most experienced aviators are susceptible
to binocular rivalry problems. However, a rested aviator is less susceptible
than a tired aviator.
(4) The periodic use of a tinted visor can aid in reducing visual
distractions.
(5) If all else fails to aid in controlling rivalry, the aviator may have to
close one eye until the rivalry subsides.
f. Scanning Techniques. Proper scanning techniques are essential during FLIR
night flights. The discussion of scanning techniques in Chapter 1 and FM 1-301 is
general. The general scanning techniques for unaided flight also apply to PNVS
operations. However, the aviator should consider a few additional techniques
when he uses the PNVS for night flight.
(1) To overcome the limited field of view (30 by 40 ) and loss of
peripheral cues, the aviator must use a continual scanning pattern during
terrain flight. While the aircraft is moving, the aviator should look left and
right of the aircraft centerline while maintaining reference with the
symbolic head tracker. The length of time and frequency of the scanning
pattern will be based on the type of terrain and obstacles, airspeed, and
scene content quality of the PNVS.
(2) While scanning, the aviator should use close cues to determine the
altitude needed for obstacle clearance and to determine airspeed and
closure rates. He should use mid-range and far cues to evaluate route
trends; for example, direction, turns, and obstacles. The aviator should
avoid overflying the close-in cues and maintain obstacle clearance.
(3) The aviator should use both the aided eye and the unaided eye for
obstacle detection and avoidance. The inability of the FLIR to see lights
can be overcome by incorporating the unaided eye into the scanning
pattern.
(4) While scanning, periodically changing FLIR sensor polarity will assist
in distinguishing obstacles such as other aircraft, tree branches, and poles.
These may be difficult to detect because of DC restoration. DC restoration
(horizon blooming) causes a washing out of the upper portion of the video
image during rolling maneuvers when the bank angle is increased.
(5) Practice and experience are needed to obtain maximum visual
information from both the aided eye and the unaided eye. The aviator must
learn to correctly interpret and use flight symbology for aircraft control.
Reliance on imagery alone or dependence on unaided vision is insufficient
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and will result in erratic aircraft control. Unaided peripheral vision in the
aided eye may be distracting until the aviator learns to use primarily the
FLIR cues and symbology and to disregard unwanted peripheral
distractions.
g. Spatial Disorientation. Maneuvers requiring large bank angles or rapid attitude
changes tend to induce spatial disorientation. To avoid this condition, the aviator
should not execute drastic changes in attitude and bank angle. The aviator flying
with the PNVS may become disoriented and experience an unusual attitude when
he has visual reference with the earth's surface with the FLIR sensor. This can
also occur when he loses such refer-ence as a result of FLIR image degradation or
sensor failure. Proper scanning techniques using a slow, purposeful head
movement and positive aircraft control with the proper symbology mode will aid
in preventing spatial disorientation.
(1) Crew coordination is important during the recovery from spatial
disorientation. It should be preplanned and prebriefed to conform to the
crew's capabilities.
(2) Regardless of the symbology mode being employed at the time of
disorientation (hover, bob-up, transition, or cruise), the initial recovery
steps should be the same. The crew should orient the PNVS turret toward
the nose of the aircraft and minimize head movement during the recovery.
The head tracker should be located and cross-checked with the LOS
reticle. The crew can use the remaining flight symbology to complete
reorientation and recovery.
h. Airspeed and Ground Speed Limitations. Aviators using thermal- imaging
systems tend to overfly their capability to see. To avoid obstacles, aviators must
understand the relationship between the system's visual range, atmospheric
conditions, and airspeed.
WARNING
The visual range of thermal-imaging systems may not allow aviators
enough time to avoid obstacles. Therefore, aviators must exercise
extreme care when using the systems during terrain flight modes.
Aviators should reduce ground speed so that they can detect and
avoid obstacles when thermal resolution is poor because of
atmospheric conditions.
(1) Different atmospheric conditions will affect the distance at which
aviators can identify an object. This, in turn, limits the ground speed at
which aviators can safely fly at terrain flight altitudes.
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(2) Object acquisition and identification are related to atmospheric
conditions and thermal contrast. Variables that affect the ability to see
with thermal-imaging systems include-•
•
•
•
•
•
Infrared crossover.
FLIR sensor optimization.
Minimum resolvable temperature.
Aviator's proficiency and capabilities.
Moisture content in the air (humidity).
Atmospheric obscurations (dust, smoke, haze).
i. Weather.
(1) While total scene obscuration rarely occurs when using FLIR systems,
aviators may fail to detect entry into IMC. This is because the FLIR will
enable them to see through obscurations such as fog, rain, haze, dust, and
smoke. When encountering atmospheric obscurations, the aviator should
use caution not to "overfly" the FLIR. As FLIR quality degrades, the
aviator must remember to slow down to allow increased reaction time for
obstacle avoidance.
(2) The aviator may detect a reduction of scene quality and an increasing
graininess in FLIR quality. This would indicate an increasing density in
the obscuration or equalizing temperature in the scene being viewed.
When the aviator recognizes his visibility is being restricted, he should
attempt to reoptimize the FLIR, using the level and gain controls. If
reoptimization of the FLIR does not improve scene quality, the aviator
must turn out of the obscuration, land, or execute IMC recovery
procedures.
j. Weapons.
(1) Target acquisition and detection. Detection of targets at night with the
FLIR system is fairly easy. However, the identification of those targets is
often difficult. Some of the basic considerations which may aid in target
acquisition and detection are discussed below.
(a) PNVS. The pilot can aid the CPG in detection by using the
PNVS. However, the pilot's primary responsibility is to fly the
aircraft. Because the PNVS has no magnification capability, the
maximum range the pilot can detect during optimum conditions is
about 1,500 to 2,000 meters.
(b) TADS FLIR. The TADS FLIR is the primary night acquisition
source for the AH-64. It is a passive night viewing device with
four different fields of view. The CPG's ability to optimize and
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operate the TADS FLIR directly influences his capability to detect
targets. The use of "white hot" polarity can normally best be
optimized for target detection.
(2) Weapons firing effects.
(a) Rocket. During rocket firing, the motor burn from the rocket
will illuminate the cockpit area and some sparkling effect can be
seen to the front of the aircraft. Other than this momentary
distraction to the unaided (left) eye, the crew should not experience
any adverse effects.
(b) 30-millimeter cannon. The muzzle blast from the 30-millimeter
cannon may be a source of distraction to the unaided (left) eye if
the gun is fired off-axis. This is a temporary distraction and can be
minimized by crew coordination and communication.
(c) Hellfire missile. During Hellfire missile firings, the crew will
experience a temporary illumination of the cockpit area similar to
rocket firings. This temporary distraction from the flight motor of
the missile will not affect either crew member's aided (right) eye,
which is already adapted to photopic vision.
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CHAPTER 3
HEMISPHERICAL ILLUMINATION AND METEOROLOGICAL CONDITIONS
Night aviation operations are more easily conducted when ambient light sources provide
the greatest amount of hemispherical illumination. The aviation unit operations officer,
with the assistance of supporting Air Force weather personnel, can develop a light-level
calendar to predict when optimum levels of ambient light will exist. Sources of ambient
light include the moon, background illumination, artificial light, and solar light.
Regardless of the ambient light source, meteorological conditions will affect the level of
light.
3-1. LIGHT SOURCES
The two principal light sources for night aviation operations are natural and artificial.
Each type is discussed below.
a. Natural. The moon is the most important source of natural light at night. The
sun provides light usable at certain times. The stars provide some background
illumination.
(1) Lunar light. At night the moon provides the greatest source of ambient
light. The moon rises in the east and sets in the west. The moon angle
changes about 15 per hour (1 every four minutes). The ambient light level
changes as the moon angle changes. Light from the moon is brightest
when the moon is at its highest point (zenith). The time at which the moon
rises and sets changes continually. Detailed planning is required to
determine what the ambient light levels will be during a particular night
flight. The pink light filter or infrared band-pass filter must be installed
and operational on the aircraft when flight is conducted with I2 devices
and the ambient light level is less than 2.5 millilux (USAREUR only). The
same is true when moon illumination is less than 23 percent or the moon is
below 30 on the horizon. During the flight, the aviator determines whether
to use the light based on the prevailing conditions. Conditions during each
of the four phases of the moon conform to a distinct pattern, as shown in
Figure 3-1.
(a) New moon. The new moon phase is completed in about eight
days. Moonlight increases toward the end of the phase when about
50 percent of the moon is illuminated. A low light level exists.
(b) First quarter. About seven days are required to complete the
first quarter phase. The percentage of moon illumination at the
beginning of the phase is about 50 percent. This increases until
slightly less than 100 percent of the apparent disk is illuminated.
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(c) Full moon. The full moon phase begins when 100 percent of
the disk is illuminated. It ends seven days later when about 50
percent of the moon is visible.
(d) Third quarter. The duration of the last phase (third quarter) is
about seven days. It begins when about 50 percent of the moon is
visible and ends when 2 percent or less is visible.
Figure 3-1. Phases of the moon
(2) Solar light. Ambient solar light is usable for a period following sunset
and before sunrise. After sunset, the amount of available solar light
steadily decreases until the level of light is not usable to the unaided eye.
Solar ambient light becomes unusable when the sun is 12 below the
horizon. This is called the end of evening nautical twilight or EENT.
Before sunrise, solar light becomes usable when the rising sun is 12 below
the horizon. This is called the beginning of morning nautical twilight or
BMNT.
b. Artificial. Lights from cities, automobiles, fires, and flares are normally sources
of small amounts of illumination. The lights of a large metropolitan area will,
however, increase the light level around the city. The light from these sources is
most pronounced during overcast conditions.
3-2. METEOROLOGICAL EFFECTS
Because meteorological conditions vary, the light level cannot always be accurately
predicted. A flight may begin with clear skies and unrestricted visibility, but
meteorological conditions may deteriorate during the flight. Visibility restrictions can
occur gradually or suddenly. Adverse weather at night is difficult to detect, and a gradual
loss of horizon or decrease in visual acuity may occur as weather conditions worsen. As
VMC deteriorate, aviators must reduce airspeed to prevent inadvertent entry into IMC.
Aircrews should be constantly aware of changing conditions. An awareness of these
limiting factors will assist in evaluating the available ambient light. FM 1-230 contains
details about meteorological conditions.
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a. Clouds.
(1) Clouds reduce hemispherical illumination to some extent. The exact
amount of reflection or absorption of light energy by different cloud types
is not known. Therefore, a common factor cannot be applied to each
condition of cloud coverage. A subjective evaluation of light reduction
caused by clouds can be made by considering the amount of cloud
coverage and the density, or thickness, of the clouds. For example, a thick,
overcast layer of clouds will reduce the ambient light to a much greater
degree than a thin, broken layer of clouds. The combined effects of two or
more layers of clouds must also be considered.
(2) Because of reduced night vision (unaided or aided), aviators may fail
to detect a gradual increase in cloud coverage and may, without warning,
inadvertently enter the clouds. At night aircrews must be alert for
indications that clouds are present. Some of these indications are discussed
below.
(a) The light level is gradually reduced. Visual acuity and terrain
contrast are also reduced or lost.
(b) The moon and stars are obscured. The less visible the moon
and stars, the heavier the cloud coverage.
(c) Shadows obscure the moon's illumination. Crew members can
detect these shadows by observing the varying levels of ambient
light along the flight route.
b. Fog, Dust, Haze, and Smoke.
(1) Visibility restrictions reduce hemispherical illumination. Conditions
such as ground fog, dust, haze, or smoke are more pronounced at lower
altitudes. Haze is common around large cities.
(2) The probability of fog increases as the temperature decreases and the
dew-point spread approaches zero. A decrease in the intensity of ground
lights indicates an increase in the moisture content of the air. A halo effect
around ground lights indicates that moisture is in the air and that ground
fog may be forming. The halo effect is more pronounced with I2 devices.
Aviators using I2 devices can "see" through fog, snow, and rain better than
with the unaided eye. This may result in less reaction time for the aviator
to avoid entering IMC.
c. Lightning. At least one meteorological phenomenon increases illumination.
Lightning flashes have an effect similar to that of a bright flare. The intensity of
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the illumination depends on how near the lightning is. Night vision may be
impaired if the aircrew is too close to lightning activity.
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CHAPTER 4
TERRAIN INTERPRETATION
The I2 device, the ambient light level, and night vision techniques influence how well
aircrews can interpret the terrain at night. Different conditions affect the visual
presentation of natural and man-made features during both unaided and aided flight. This
chapter discusses the factors that affect night terrain interpretation and how to
compensate for their limitations. FM 1-202 discusses the environmental conditions that
affect flight.
4-1. VISUAL RECOGNITION CUES
The ability to detect a natural or man-made feature at night depends primarily on object
size, object shape, and contrast. Equally important is the effective use of night vision
scanning and viewing techniques.
a. Object Size. Large structures and terrain features, such as churches and rivers,
are easier to recognize at night than small objects. For example, a small object,
such as an observation helicopter, is difficult to identify because it can become
lost in the background. Figure 4-1 illustrates identification by object size. To see
and recognize small features, crew members must view the area several times. A
shorter viewing distance also aids in visual recognition.
Figure 4-1. Identification by object size
b. Object Shape. Aircrews can identify objects at night by their shapes or
silhouettes. Figure 4-2 illustrates identification by object shape. Buildings can
sometimes be recognized at night by their architectural design. For example, in
the United States the silhouette of a building with a high roof and a steeple is
easily recognizable as a church. Churches in other parts of the world, however,
may have low-pitched roofs with no distinguishable features. Man-made features
depicted on the map can help aircrews recognize silhouettes. When shape is used
to identify an object, the aviator may have to change the aircraft's position to
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obtain a different viewing perspective. For example, a tank may not be
recognizable from the front but may be easily recognizable from the side. The
shape of terrain features is also a means of identification at night. Landmarks,
such as a bend in the river or a prominent hilltop, provide distinct shapes that aid
in night terrain interpretation.
Figure 4-2. Identification by object shape
c. Contrast. The contrast between an object and its background can aid in object
identification. The degree of contrast, however, depends on the available ambient
light, texture of the object, and luminance of the object and its background. Figure
4-3 illustrates identification by contrast.
(1) Ambient light. The ambient light level affects the degree of contrast
between objects. The higher the light level, the greater the contrast. As the
ambient light increases, more light is reflected and shades are more
pronounced. Objects with a poor reflective surface appear black during
low light levels and dark gray during high light levels. Objects or terrain
features with good reflective quality appear gray during low light levels
and become progressively lighter as the ambient light increases.
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Figure 4-3. Identification by object contrast
(2) Color, texture, and background. The color, texture, and background of
a man-made or natural feature determine its reflective quality. The various
reflective qualities of objects in a field of view help determine the degree
of contrast. An unplowed field with no vegetation provides a good
reflective surface. An area covered with dense vegetation provides a poor
reflective surface. A crew member familiar with the reflective quality of a
feature may be able to identify it by contrast. Man-made and natural
features most identifiable by contrast include roads, water, open fields,
forested areas, and desert.
(a) Roads. The surface of some dirt roads provides excellent
contrast with the surrounding terrain. Roads cut through heavily
forested areas are easily identifiable if visible through foliage. The
light color of concrete highways, normally an excellent reflective
surface, is easily identifiable during most light-level conditions.
Asphalt roads are usually difficult to identify because the dark
surface absorbs available light. In desert areas, however, the
surrounding contrast can make asphalt roads readily detectable.
(b) Water. Very little color contrast exists between a landmass and
a body of water during low light conditions. When viewed from
the air, lakes or rivers appear dark gray. As the light level
increases, water begins to change color and the contrast between
the land and water increases. Moonlight reflected off the water is
easily detected. When surface wind is present, the ripples on the
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surface intensify the reflection off the water. This provides
additional contrast and aids in terrain identification.
(c) Open fields. Contrast may be very poor in fields covered with
vegetation. Most crops are dark-colored and absorb light. During
the harvest or the dormant season, the color of the vegetation
changes to a lighter color and contrast with the surrounding terrain
improves. The coarse texture of a freshly plowed field will absorb
light.
(d) Forested areas. Heavily forested areas do not reflect light and
generally appear as dark areas at night. Because heavy vegetation
provides no contrast, forests conceal objects and terrain features.
However, excellent contrast is evident between deciduous and
coniferous trees as well as between open fields and surrounding
forested areas.
(e) Desert. During high illumination, mountain ranges are easily
identifiable. The dark color of barren mountains provides an
excellent contrast with the light color of the desert floor. Lower
rises in terrain between the viewer and the higher ranges are,
however, difficult to identify in low ambient light.
4-2. INTERPRETATION FACTORS
The ability to use cues for terrain interpretation is affected by a number of factors. These
include ambient light, viewing distance, flight altitude, moon altitude, visibility
restriction, terrain, and seasons.
a. Ambient Light. Reduced light levels at night decrease visual acuity. This
restricts the distance at which an object can be identified. Terrain interpretation by
size, shape, and contrast becomes more difficult as the light level decreases.
Reduced airspeeds will improve visual interpretation and increase viewing and
reaction time.
b. Viewing Distance. The viewing angle becomes smaller as the distance from the
object increases. Therefore, large and distinctly shaped objects may become
unrecognizable when viewed from a great distance at night. Figure 4-4 illustrates
identification by object viewing distance. Range is also difficult to estimate at
night and can result in a miscalculation of the object's size. The distance at which
interpretation of an object becomes unreliable also depends on the ambient light
level. An object that can be identified by its shape and size at a distance of up to
1,500 meters during a high light condition may be unrecognizable at 500 meters
during a low light condition.
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c. Flight Altitude. The altitude at which an aircraft is flown affects the aircrew's
ability to interpret the terrain. The effects of high and low altitude flights are
discussed below.
(1) High altitude. The ability to identify man-made or natural features
progressively decreases as the flight altitude increases. This condition is
affected by all levels of ambient light. When the flight altitude increases,
contrast between features becomes less distinguishable and features tend
to blend together. As terrain definition becomes less distinct, detection
from altitude becomes difficult. Changes in the viewing angle and the
distance at which the object is being viewed will change the apparent
shape of an object.
Figure 4-4. Identification by object viewing distance
(2) Low altitude. Terrain becomes more clearly defined and contrast is
greater when the aviator flies closer to the ground. Thus man-made and
natural features are more easily recognized and navigational capability is
improved. The area that a crew member can view at low altitudes,
however, is smaller than that at higher altitudes. At low altitudes, the
aviator may have to reduce airspeed to permit more accurate terrain
interpretation. The aviator can also identify objects by silhouetting them
against the skyline at low altitudes.
d. Moon Altitude.
(1) High altitude. The higher the altitude of the moon, the greater the
illumination. An increased ambient light level improves visual acuity and
contrast. Shadows that cause distortion and the loss of ambient light
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decrease at this time. The best conditions for visual interpretation for any
phase of the moon exist when the moon is at its highest altitude.
(2) Low altitude. Terrain interpretation is more difficult when the moon is
low on the horizon. This is due to the lower light level that prevails and
the shadows that form. If low-level flight is conducted toward the moon
when it is low on the horizon, the aircrew may be bothered by glare. Glare
distorts vision and can cause a loss of dark adaptation. During aided flight,
glare will also degrade the capability of the I2 device used. When the
moon is low on the horizon, terrain features or objects visible along the
skyline are more recognizable.
e. Visibility Restriction.
(1) Such conditions as dust, rain, fog, and snow can restrict visibility.
These, in turn, reduce the ambient light level and result in a loss of visual
acuity. Visibility restrictions normally occur gradually. Initially, the visual
range is reduced followed by a loss of terrain definition. As visibility
decreases, night vision may become so impaired that terrain flight should
be discontinued.
(2) Dust, rain, fog, and snow affect operations similarly. Light reflecting
off blowing dust and snow particles may cause tiny pinpoints of light.
Dust and snow swirling from rotor downwash may cause the illusion of
relative motion even if the aircraft is in a stable hover. The scan pattern
should include any visible fixed reference points that have vertical relief;
for example, bushes, trees, and rocks.
f. Terrain. The nature of the terrain will determine the amount of light reflected
from the earth's surface. Deserts, rolling terrain, and mountains are examples of
the different types of terrain that affect light reflectivity.
(1) Deserts. The texture and color of the soil of the desert floor provide
optimum reflectivity of available ambient light and identification of
objects by contrast. Man-made or natural features that appear on the desert
floor are easily recognizable. Flight altitude normally is lower; thus,
terrain interpretation is improved. Visibility restrictions are not common.
However, depth perception will be poor. Desert terrain provides a
minimum of contrast because vegetation is limited. During high winds,
blowing sand significantly restricts terrain interpretation.
(2) Rolling terrain (heavy vegetation). Terrain interpretation is difficult
over rolling terrain because of the lack of recognizable terrain features.
Contrast is good between forested areas and open fields. Rivers and terrain
features that are distinctly different in elevation from the surrounding
terrain provide the most recognizable natural landmarks for navigation.
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Dirt roads and farm structures provide the most distinguishable man-made
features. To improve terrain interpretation, the aviator must reduce
airspeed. However, he will normally fly higher to increase the aircrew's
ability to detect obstructions.
(3) Mountains. Terrain identification can best be accomplished where
rapid changes in elevation occur such as in mountainous areas.
Silhouetting objects against the skyline enhances recognition of objects
and terrain features. Decreased ambient light can be anticipated in valleys
and on the backside of mountains when the moon is low on the horizon.
Contrast is poor in areas of heavy, homogenous vegetation. Barren
mountains reflect ambient light so contrast is improved. During high light
conditions, navigation is easier. However, airspeed normally will be
slower in mountainous regions because rapidly changing terrain requires
corresponding altitude changes.
g. Seasons. The seasons of the year affect the amount of ambient light reflected
from the earth's surface. Conditions during winter and summer are discussed
below.
(1) Winter.
(a) Contrast improves during the winter because farm areas lack
vegetation. Contrast is also improved when snow covers the
ground. Snow increases total illumination because it may reflect
ambient or artificial light. The light color of the snow, compared
with the dark color of structures and heavy forested areas,
enhances visual interpretation.
(b) The loss of foliage on deciduous trees makes ground features,
such as small streams, easier to identify. Plants and grass that
cover open fields change in color and improve the contrast
between open fields and coniferous trees. However, barren trees
reflect less light and are, therefore, harder to see. Because of this
safety hazard, the aviator may have to fly higher.
(c) During the winter, the orbital path of the moon is closer to the
earth. The ambient light level is higher than at any other time of
the year. This improves visual acuity, which enhances terrain
interpretation.
(d) Cloud coverage and restricted visibility are more likely to occur
during the winter than during the summer. Both conditions
significantly reduce the ambient light level. This, in turn, decreases
visual acuity and makes terrain interpretation more difficult unless
sources of artificial light, such as cities and towns, are nearby.
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(e) During extreme cold, a heavy buildup of snow may conceal
man-made and natural terrain features. A snowdrift may obscure a
road intersection that otherwise provides a good navigation
checkpoint. The aircrew can identify an object by associating it
with other objects or terrain features. A power line, a fence line, or
a cut through a forested area will aid the aircrew in locating the
road intersection. Small rivers and lakes indicated on the map may
become frozen and covered with snow and therefore
unrecognizable. The aircrew can make positive identification only
by associating the relative position with terrain features such as a
depression or a tree line.
(2) Summer. Generally, identifying objects and terrain features by contrast
in the summer is less effective than in the winter. This is caused by the
increased amount of vegetation in open fields and a new growth of foliage
on deciduous trees. Small rivers and streams are difficult to recognize. The
aircrew may also be unable to recognize military targets when they are
located in or near forested areas.
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CHAPTER 5
NIGHT OPERATIONS
This chapter implements portions of STANAG 2999 (Edition One) and AIR STD
44/33B.
Flight operations at night are conducted essentially the same as during the day. However,
night operations are more hazardous because of visual limitations. These limitations
impose stricter requirements on aircrews when they plan and execute night missions. This
chapter discusses the effects of visual limitations on aircrews. It also discusses preflight
considerations, night flight techniques, and emergency and safety procedures.
Section I
PREMISSION PLANNING
5-1. MISSION BRIEFING AND DEBRIEFING
a. Briefing. Aircrew mission briefings are conducted according to AR 95-1, other
appropriate regulations and directives, and the unit SOP. All missions are briefed.
b. Debriefing. At the end of the mission, a thorough debriefing should be
conducted. The debriefing should include problems encountered during the flight
and recommended solutions and lessons learned during the mission or maneuvers.
5-2. CREW DUTIES
The PC is responsible for assigning crew duties before a night flight. These duties should
also be outlined in the unit SOP. Figure 5-1 shows a sample of crew duty assignments.
5-3. COMMON TERMINOLOGY
Common terminology must be established among the mission participants. The
terminology will vary based on the type of mission flown. Unit SOPs should identify
standard terms used by the aircrews during flight.
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Figure 5-1. Sample of crew duty assignments
Section II
PREFLIGHT GUIDELINES
5-4. PREFLIGHT INSPECTION
The aircraft preflight inspection is a critical aspect of mission safety. The inspection must
comply with the appropriate aircraft operator's manual.
a. The preflight inspection should be scheduled during the day when possible.
During a night preflight inspection, a flashlight with an unfiltered lens should be
used to supplement available lighting. If a red or blue-green lens is used, oil and
hydraulic fluid levels and leaks will be difficult to detect.
b. Windscreens should be checked to ensure they are clean and relatively free of
scratches. Windscreens slightly scratched may be satisfactory for day flight but
are not acceptable for night flight. Glass windscreens that resist scratching are
more desirable for night flight. The searchlight or landing light should be
positioned so that the best possible illumination will be provided during an
emergency descent.
NOTE: Adequate time should be allowed so that crew members can dark-adapt after
completing the preflight inspection.
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5-5. AIRCRAFT LIGHTING
The use of aircraft lights should be standardized to reduce the adverse effects of these
lights on night vision. AR 95-1, the appropriate ATM, and the appropriate aircraft
operator's manual will aid in the standardization effort.
a. Cockpit Lights.
(1) During prestart checks, cockpit lights should be adjusted to the lowest
intensity level that will allow the instruments to be read. For aided night
flight, aircraft interiors must be modified according to modification work
orders. Interior lighting, supplemental lighting, or flashlights assist in
illuminating the cockpit and the cabin area. During the engine-start
sequence for aircraft equipped with electric starter motors, the engine
instrument lights should be turned brighter because of the dimming effect
when the starter is engaged. If a particular light is too bright or causes
reflection, it should be turned off or modified. All lights not required for
safe flight should be turned off.
(2) As the ambient light level decreases from twilight to darkness, the
intensity of the cockpit lights should be reduced to the lowest readable
level. This will reduce the reflection of the lights off the windscreen. For
aircraft equipped with a BRIGHT-DIM switch, which controls the
intensity of the caution panel warning lights, the DIM mode should be
selected for night flight.
(3) A flashlight, with appropriate lens filter, or the map light can
supplement the available light in the cockpit. If the map/utility light is
used, it should be hand-held or remounted to a convenient location. A
flashlight is required in the aircraft per AR 95-1.
b. Anticollision Lights. In flight formations, these lights should be turned off
except for those on the trail helicopter. When IMC is entered, the anticollision
lights may be turned off. Operation of the anticollision lights during these
conditions tends to induce distraction and may cause flicker vertigo. Commanders
may authorize anticollision lights to be turned off during training if the procedure
is explained in the unit SOP. AR 95-1 discusses the use of anticollision lights.
c. Landing Light or Searchlight.
(1) During training, the aviator may turn on either light as necessary.
However, the landing light or searchlight may reduce visibility under
certain atmospheric conditions. If that occurs, the aviator should not turn
on the landing light or searchlight until it will be effective. Use of an
unfiltered landing light or searchlight will result in a noticeable loss of
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night vision. If flight is to be continued at low altitude, enough time
should be allowed for the aircrew to dark-adapt.
(2) During tactical operations, the landing light or searchlight should only
be used to prevent a hazardous situation from developing. The potential
benefit of using the light must be evaluated. Any benefit gained must
outweigh the potential for, and consequences of, detection by the Threat.
d. Position and Navigation Lights. Unmodified navigation and position lights
create a halo around the fuselage. They degrade night vision and increase the
possibility of detection by the Threat. Position lights must be used during training
except in an authorized and approved "blackout" training area. Aircrews
conducting multihelicopter operations in high ambient light conditions should
adjust their position lights accordingly. All lights should be modified to emit a
low-intensity light. AR 95-1, AR 95-2, and Federal Aviation Regulations discuss
the use of position and navigation lights. Appendix D discusses lights-out night
training.
5-6. AIRCREW PREPARATION
Proper preparation of the aircraft and ground facilities for night flight contributes greatly
to the success of the mission. However, the mission may fail unless crew members are
physically and mentally prepared to participate in the night flight. To ensure readiness,
crew members should-•
•
•
•
•
•
Dark-adapt before flight.
Avoid self-imposed stress.
Avoid bright sunlight during the day.
Learn and use the principles of night vision.
Avoid all bright lights after dark adaptation.
Participate in frequent night flight training.
Section III
NIGHT FLIGHT TECHNIQUES
5-7. LIMITATIONS
a. Visual reference outside the aircraft is limited at night. Movement of the
helicopter is difficult to detect because night terrain features often blend into one
solid background. Hover altitude and ground track are also difficult to estimate.
The degree of difficulty depends on the ambient light level and the aircraft's
altitude.
b. Equipment, instruments, and control switches are easily located in a lighted
cockpit. However, aviators should be able to locate and use all cockpit equipment
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associated with immediate action emergency procedures without the aid of lights.
This ensures that the proper control switch can be identified during an emergency.
The use of artificial lights (chemical light sticks or flashlights) is recommended if
time permits. The location of radios, mission equipment, and switches must be
standardized so they can be identified when needed.
c. Visual references that provide positive identification during the day may be
difficult to see at night. Objects that emit illumination, such as airport beacons
and towers with obstacle lights, are prominent night navigational aids.
d. Visual flight is more demanding over sparsely inhabited areas with few ground
lights. As the altitude above the ground increases, visual references are less
effective and aviators must rely more on instruments.
e. Reduced visual references may cause crew members to focus on a single light
or a group of lights in a concentrated area. This can induce illusions and may
cause light fixation or autokinesis. Crew members should avoid staring at a single
light source.
f. At night, aircrews may unexpectedly encounter adverse meteorological
conditions. Visibility may be restricted, and clouds may form below the flight
altitude. When ground references become obscured, aircrews should anticipate
that a layer of clouds or fog is below their flight altitude. Clouds at the same flight
level are often difficult to detect, and aviators may inadvertently enter IMC.
Emergency IMC recovery and breakup procedures must be established in the unit
SOP and briefed before each unaided or aided night flight.
g. When fully night-adapted, the eyes become extremely sensitive to light.
Exposure to a light source will cause a partial or a complete loss of night vision.
Aircrews should avoid exposure to light sources, both outside and inside the
aircraft. Also, they should avoid looking directly at or into a high-intensity light.
h. Night flying is more stressful than day flying. Therefore, crew mental and
physical fatigue during flight occurs sooner at night than during the day.
Performance and efficiency deteriorate more rapidly at night. This deterioration
causes poor coordination and slower reaction time and reduces night vision. When
possible, initial and refresher night training periods should not exceed 1.5 flight
hours. When designing a training program, commanders must consider the
experience levels of crew members. AR 95-1 contains guidance on environmental
relative factors and crew endurance.
5-8. HOVER
Aviators may have difficulty when hovering at night because visual ground references are
not easily distinguishable. The type of surface over which the helicopter is hovered
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affects an aviator's ability to judge movement. The technique used will vary with the type
of surface and type of lighting.
a. Types of Surface.
(1) Asphalt or concrete. Estimating the hover height over asphalt or
concrete is difficult because few visual cues are available to aid in height
estimation. The aviator can detect aircraft movement by observing
markings, such as runway centerlines, taxi lines, and lateral boundaries, on
the hard surface area. Movement is easier to judge where contrast exists
between the hard surface and grass areas along the lateral boundaries.
Fixation may cause spatial disorientation. Therefore, the aviator should
avoid staring at a particular reference.
(2) Grass. Aviators will find it difficult to maintain altitude and a constant
position while hovering over an open, grass-covered area. Contrast may be
poor and few references may be available to use in estimating vertical or
horizontal movement. Tall grass presents an even more difficult problem.
The grass, blown by the rotor wash, will have a continual waving motion.
This creates an illusion of movement, making it difficult for the aviator to
maintain a stationary hover point. Also, aviators tend to hover at a higher
altitude than is necessary over tall grass and to inadvertently move
laterally with the movement of the grass.
(3) Water. Water is the most difficult of all surfaces from which to judge
movement during a hover. If possible, the aviator should hover the aircraft
near objects such as tree stumps, buoys, shorelines, or a reference marker
thrown into the water. Aviators tend to move laterally with the waves.
Accurate estimation of height is difficult, if not impossible, without a
radar altimeter.
b. Types of Lighting.
(1) Hovering with position lights.
(a) When hovering with the aid of position lights, aviators tend to
stare at a single reference point on the ground. Aviators should
select reference points to the front and sides of the helicopter. By
con-tinuous scanning, the aviator ensures that all available
references are used to detect movement of the helicopter.
(b) When hovering with the position lights on DIM, aviators tend
to hover too low. This situation is difficult to overcome when
ground references are not visible. The aviator must continuously
scan perpendicular to the direction of the hover, looking for cues
that will indicate forward speed. If hovering on a runway or
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taxiway, aviators should use lights at the sides of the aircraft to
estimate forward speed. On some aircraft, however, the position
lights provide little or no supplemental lighting.
(2) Hovering with landing light or searchlight.
(a) If the landing light or searchlight is on during a hover, ground
references will be visible. The aviator can thereby detect
movement of the helicopter over the ground and estimate the
height of the hover. During a hover at night, references will be
limited to the area illuminated by the light.
(b) The position of the landing light or searchlight significantly
affects the aircrew's night vision. When the beam of light is viewed
directly, as much as 45 minutes may be required for the aircrew to
dark-adapt after the light is extinguished. The landing light or
searchlight can be adjusted to provide adequate lighting and allow
the aircrew to avoid looking directly at the light beam. This will
assist in maintaining dark adaptation.
5-9. TAKEOFF
a. If enough illumination is available to view obstacles, the aviator can
accomplish the takeoff the same as a normal takeoff during the day. Figure 5-2
shows a night takeoff. If illumination is insufficient to view obstacles, the aviator
should make an altitude-over-airspeed takeoff until the aircraft reaches an altitude
that will clear the obstacles. The takeoff may be performed from a hover or from
the ground. The aircrew should treat visual obstacles, such as shadows, the same
as physical obstacles.
b. If the aviator uses more than hover power for the takeoff, he should maintain
that power setting. Approximately 10 knots before reaching the desired climb
airspeed, the aviator should adjust power to establish the desired rate of climb and
airspeed. The crew member not on the controls should cross-check the aircraft
instruments.
c. The lack of visual references during the takeoff and throughout the ascent at
night may make it difficult for the aviator to maintain the desired ground track.
Knowing the surface wind direction and velocity will assist in maintaining the
desired ground track. Unless the wind and obstacles are a factor, the aviator
should plan the takeoff heading in the direction of the first leg of the flight route.
This will aid him in initial orientation on the first leg of the flight during periods
of low illumination.
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Figure 5-2. Night takeoff
d. During the takeoff, the aviator can use the landing light or searchlight to detect
obstacles. As the helicopter ascends, the illuminated area will increase and the
light intensity will decrease. The aviator should position the landing light or
searchlight far enough in front of the helicopter to illuminate obstacles along the
flight path. As the helicopter ascends above the obstacles, he should turn off the
light. Upon extinguishing the landing light or searchlight, the aviator should be
prepared for a sudden reduction in night vision. The aviator can ensure positive
control of the helicopter during the transition by cross-checking the flight
instruments. As the aviator's night vision improves, he can use outside references
to determine the helicopter's attitude.
e. Takeoffs in severe dust or snow conditions are extremely hazardous because
ground references may be obscured. The aviator should perform an instrument
takeoff until clear of the obscuration.
5-10. EN ROUTE
a. Unaided. After reaching the desired flight altitude during unaided flight, the
aviator should allow adequate time to adjust to the conditions of the flight. This
includes readjustment of the instrument lights and orientation to outside
references. During the adjustment period, the aircrew's night vision will continue
to improve until optimum dark adaptation is achieved.
b. Aided. The viewing distance increases with altitude. However,
depth perception and visual acuity decrease significantly at higher flight altitudes.
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NOTE: The crew member not on the controls should maintain a cross-check of aircraft
instruments.
5-11. LANDING
Because vision is reduced at night, night LZs should be larger than those used during the
day. Also, LZs should be relatively clear of obstacles on the approach and takeoff paths.
Aviators should observe the contrast between the dark trees and the lighter open area
when making an approach without aircraft lights into an open field. This aids in the
identification of obstacles along the boundary of the LZ. The forward and lateral limits of
the LZ will appear darker when contrasted with the open area.
a. Altitude, apparent ground speed, and rate of closure are difficult to estimate at
night. Throughout an approach, other crew members should provide information
to the aviator about obstacle avoidance, altitude, airspeed, and the approach angle.
Viewing through the side window aids in estimating the rate of closure of the
helicopter. If the approach is made to tactical lights, lateral movement can be
detected by the relative position of the helicopter and the lights. Except in
blowing dust or snow conditions, night approaches to an unlighted area should be
terminated at a hover and followed by a slow vertical descent to the ground.
b. Height perception and rate of closure are more easily determined during
approaches at night made with the landing light or searchlight. However, the
landing light or searchlight should not be used in fog, haze, or other conditions
that restrict visibility. This is because light will be reflected into the cockpit and
may cause a safety hazard or spatial disorientation.
c. The approach can be made to the ground or terminated at a hover. Approaches
to the ground require the greatest proficiency. Because the condition of the
landing surface is difficult to determine at night, approaches to field LZs normally
are planned to terminate at a hover. If, during the approach, the aviator finds the
landing area suitable for the touchdown, he may continue the approach to the
ground. Forward cyclic is required after passing through ETL to ensure the
helicopter continues in forward motion. As the helicopter nears the ground, it
becomes difficult to estimate when contact will occur. Most aviators tend to
"milk" the helicopter down. This technique requires more time to get the
helicopter on the ground and usually results in overcontrol of the helicopter. To
avoid this situation, the aviator should reduce collective pitch gradually, but
continuously, as he terminates the approach.
d. Night approaches to a snow-covered surface normally are made to a reference
point on the ground; for example, a tactical landing light or runway light. These
lights provide a good reference for judging the angle of descent and the rate of
closure. When executing a night approach to a tac-tical landing site with lights,
the aviator should always plan the approach to land short of the touchdown point.
This procedure ensures that the aviator will not overshoot and have to decelerate
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rapidly in a snow cloud. By shooting short, the aviator can maintain airspeed after
the level-off, thus keeping the aircraft in front of the snow cloud until touchdown.
Figure 5-3 compares a snow approach and a normal approach. If the landing light
or searchlight is used during the approach, it should be positioned so that the
beam is beneath the aircraft. Additionally, a touchdown point (lighted or
unlighted) in the middle of a snow-covered field may provide insufficient contrast
and depth perception cues. Therefore, the aviator may need to select a touchdown
point near a tree line or other feature that provides adequate contrast and depth
perception cues.
Figure 5-3. Snow approach
e. When landings are made without the landing light or searchlight, the position
lights on BRIGHT may effectively illuminate the landing area during later phases
of the approach. This illumination significantly aids in esti-mating the altitude of
the helicopter during the termination of the approach. When the position lights are
operated on DIM, effective illumination occurs closer to the ground.
f. An aviator executing a night landing to a field landing site must carefully
consider the problems involved. He should select the touchdown point before
reaching the entry point on the approach. If landing on a lighted runway or
taxiway, the aviator should select a specific grouping of lights. The apparent
ground speed and rate of closure are difficult to judge during night operations.
The last portion of the night approach should be slower than during the day to
avoid abrupt attitude changes at low altitudes and slow airspeeds. During the
approach, the aviator may accidently reduce airspeed at too high an altitude. He
should cross-check the airspeed indicator during the initial phase of the approach
to maintain the proper airspeed. Abrupt recovery from slow airspeeds may result
in a rapid loss of altitude when forward cyclic is applied. Coordinated control
movement of both the cyclic and the collective is required to fly the helicopter
along the desired approach path.
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g. A field lighting system provides fewer visual cues than a lighting system for a
fixed landing site. Approaches to a field LZ normally are made without a
searchlight or a landing light. The type and arrangement of lighting for a field LZ
may vary considerably. Regardless of the type of lighting device, at least two
lights should be used to identify the touchdown point. An illusion of movement
may occur when a single light source is viewed (autokinesis). The two lights
should be separated by at least 15 feet. When more than two lights are used to
mark the LZ, spacing between the lights can be reduced.
h. Two tactical field lighting configurations are used as landing aids for aircrews.
They are the inverted Y and the T. When operating with NATO aviation forces,
aircrews should anticipate that the T will be used.
(1) The inverted Y is best used for an approach initiated from terrain flight
altitudes. The flight procedures and techniques for executing an approach
to an inverted Y are discussed below. Figure 5-4 shows light cues for six
different approach alignments.
(a) Before the aircraft reaches the entry point for the approach, the
lights in the stem will appear as a single light. This sight picture
will also occur when the helicopter is on approach and below the
desired angle of descent. When the normal approach angle is
maintained, the Y appears as in part B, Figure 5-4. If the distance
between the lights appears to increase, the approach is steepening
and the helicopter is above the desired approach angle (part C,
Figure 5-4). If the distance between the lights appears to decrease,
the approach is shallowing and the helicopter is below the desired
approach angle (part D, Figure 5-4).
(b) The aviator can determine the alignment of the helicopter with
the desired direction of landing by observing the relative position
of the front two lights in relation to the stem. If the spacing
between the front two lights and the stem is shifted to the left of
the stem, the aviator is too far to the right and should correct to the
left (part E, Figure 5-4). If the spacing between the front two lights
and the stem is shifted to the right of the stem, the aviator is too far
to the left and should correct to the right (part F, Figure 5-4). The
desired touchdown point is inside the Y with the fuselage aligned
with the stem lights. During the last 25 feet of the approach to a
field lighting system, aviators should divert their field of view
away from the lights and concentrate on acquiring ground
references.
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Figure 5-4. Approach to a lighted inverted Y
(2) The T is best used for approaches initiated from an altitude above 500
feet AGL. The flight procedures and techniques for executing an approach
to a T are discussed below. Figure 5-5 shows light cues for six different
approach alignments.
(a) The apparent distance between the lights in the stem of the T
can be used as a reference for maintaining a constant approach
angle. A change in the spacing of the lights will occur as the
approach angle changes. Before the aircraft reaches the entry point
for the approach, the lights in the stem will appear as a single light.
This sight picture may also indicate the helicopter is below the
desired angle of descent. After an approach angle is intercepted,
the stem of the T appears similar to the one in part B, Figure 5-5. If
the distance between the lights appears to increase, the approach is
steepening and the aircraft is above the desired angle of descent
(part C, Figure 5-5). If the distance between the lights appears to
de-crease, the approach is shallowing and the helicopter is below
the desired approach angle (part D, Figure 5-5).
(b) The aviator can determine the alignment of the helicopter with
the desired direction of landing by observing the stem of the T. If
the stem points to the left of the helicopter (part E, Figure 5-5), the
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aviator is too far to the right of the course and should correct to the
left. If the stem points to the right of the course (part F, Figure 55), the aviator is too far to the left and should correct to the right.
Whether the approach should be terminated in the upper left or
right portion of the T depends on the station from which the
aircraft is being flown.
Figure 5-5. Approach to a lighted T
i. Landing can also be executed to a VAPI. The VAPI is mounted on a universal
joint that adjusts from 0 to 15 above the horizontal. The green beam represents the
desired angle of descent that ensures obstacle clearance if the aviator remains
within the beam. The aviator can ensure obstacle clearance by flying on the amber
beam. However, the approach will be steeper than desired. Flight within the red
beam indicates that the helicopter is too low and may be in danger. The aviator
will observe the brightest light when he conducts flight in the center of any one of
the three beams. When within 25 feet of the ground, aviators should direct their
field of view away from the VAPI and concentrate on acquiring ground
references. Figure 5-6 shows a diagram of the VAPI.
NOTE: If the helicopter is allowed to drift to the extreme edge of the approach beams,
the light intensity will be reduced and all beams will appear amber in color. The aviator
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may think that the helicopter is high and reduce collective pitch to lose altitude. If the
error is not corrected, the helicopter may hit an obstacle along the approach path.
Figure 5-6. Approach light colors and effective distances
5-12. PATHFINDER OPERATIONS
a. When night approaches are made to a field landing site, a qualified pathfinder
should be located in the LZ. Pathfinders should set up the field landing site and,
upon request, advise the aviator about the-•
•
•
•
•
•
•
•
•
Flow of traffic.
Field elevation.
Landing zone hazards.
Landing and takeoff heading.
Suggested traffic pattern altitude.
Wind direction and approximate velocity.
Obstacles along the approach and takeoff paths.
Number of aircraft in the traffic pattern and in the LZ.
Location of parking area in relation to the touchdown point.
b. Pathfinders participating in night operations must be briefed before the mission.
For pathfinders to be most effective, they should be issued I2 devices and trained
in their use. Pathfinders should use I2 devices when other participants are using
them.
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WARNING
Pathfinder personnel engaged in aided night operations may not have
access to night vision devices. Other participants must exercise
care because pathfinder personnel may be unable to see the unlighted
aircraft clearly.
5-13. EXTERNAL LOAD OPERATIONS
External load operations can be difficult to conduct at night. Aircrews can use any of
several methods to accomplish an external load operation. Some examples are given
below. The particular method selected depends on such factors as the size of the PZ or
LZ, number and type of aircraft, amount of illumination, and type of obscuration.
a. A standard inverted Y can be positioned about 75 feet (25 meters) in front of
the hookup area for use as a reference marker. Landing to a hover should be
accomplished by planning to touch down about 75 feet behind the inverted Y.
This is shown in Figure 5-7.
b. Using the height of the load, the aviator determines the hover altitude to which
he should terminate. Using that altitude, he mentally projects (superimposes) the
inverted Y vertically to that altitude. This mental exercise will aid the aviator in
terminating above and behind the inverted Y at the appropriate point. Figure 5-8
shows the superimposed Y.
Figure 5-7. Standard inverted Y
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Figure 5-8. Superimposed Y
c. Ground crews may prepare loads for hookup or drop-off by using chemical
light sticks. A single light is placed about 75 feet (25 meters) directly in front of
the load. Additional lights are placed about 45 to the left and 45 to the right of the
load, as shown in Figure 5-9.
NOTE: Rigging crews may consider placing chemical lights on gun tubes, jeep windows,
and so on to identify them to the aircrews and to help prevent damage to the equipment.
Figure 5-9. Load drop-off using chemical sticks
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Section IV
EMERGENCY AND SAFETY PROCEDURES
5-14. BASIC CONSIDERATIONS
Emergency procedures for day flight and night flight are the same. Responding to an
emergency condition, however, will usually take longer at night. To minimize time
delays in executing emergency procedures at night, the aviator must be familiar with the
location of all the controls and switches. He must also know all immediate action
emergency steps outlined in the appropriate aircraft operator's manual. The proper use of
established safety procedures will help prevent emergency situations.
5-15. ELECTRICAL FAILURE
If a total or partial electrical failure occurs, the aircrew must execute the appropriate
emergency procedure for the aircraft being flown. The aircraft may be difficult for other
aircrews to see, so the aviator must avoid other aircraft in the traffic pattern. When on
final approach, the aviator must decide if the approach can be continued without creating
an unsafe condition for other aircraft. During the approach, the aircrew should watch the
tower for light signals.
5-16. AIRPORT TRAFFIC CONTROL LIGHT SIGNALS
When two-way radio communications with the control tower cannot be established, the
aircrew should observe the tower for light signals. The color and type of signal identify
the action required of the aviator. Figure 5-10 shows standard tower light procedures. The
aviator acknowledges the tower light signal by flashing the aircraft landing light or
searchlight.
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Figure 5-10. Light signal procedures
5-17. VISUAL NIGHT SIGNALS
Air-to-air visual signals may be used during radio failure or radio silence. They may be
used to signal an escort helicopter or the control tower. The unit SOP should identify
visual night signals to be used during emergency situations.
5-18. EMERGENCY LANDING
a. With Power. Descent to a lower altitude will aid the aircrew in locating and
identifying a suitable landing area. A suitable landing area is one that the aircrew
is familiar with from previous use or one that provides good contrast with the
surrounding area. Depending on the atmospheric conditions, the aviator may turn
on the landing light or searchlight at the appropriate altitude (200 or 300 feet).
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This will aid the aircrew in locating an LZ and identifying obstacles. The aviator
must exercise caution when fog, haze, or other obscurations are present because
use of the landing light or searchlight will degrade night vision. If using night
vision devices, the PC must decide whether to land unaided or aided. Before
landing, the PC should try to advise the controlling agency of his circumstances
and approximate location. The crew should remain with the helicopter after
landing and identify its position by using appropriate signals.
b. Without Power. During the descent, the aviator should select the most
appropriate landing area. He may turn on the landing light or searchlight,
depending on the atmospheric conditions. If time permits, the aircrew should
make an emergency call stating the situation and the approximate location of the
helicopter.
5-19. GROUND SAFETY
a. During night operations, the number of support personnel and vehicles on the
flight line should be limited to the minimum essential for mission
accomplishment. The use of ground handling equipment also should be limited.
b. When walking on the flight line at night, crew members should illuminate their
pathway. This procedure allows crew members to identify obstacles on the ground
along the pathway, to locate nearby aircraft, and to be seen by other personnel.
Good ground light discipline includes using a properly filtered flashlight.
c. During the preflight inspection, crew members should pay particular attention
to the structural components of the helicopter. Before moving forward during the
check, crew members should shine their flashlights forward to ensure that no
obstructions lie in the pathway. Serious injury can occur if caution is not
exercised during the preflight inspection.
d. When climbing upon the helicopter at night, crew members must ensure that
surfaces are clear of oil, hydraulic fluid, water, frost, and ice. Crew members must
be careful not to lose their balance and fall during the preflight inspection of the
rotor assembly.
5-20. AIR SAFETY
a. Crew members must be aware of the limitations of night vision and must not
overestimate their ability to perform duties at night. After initial qualification,
aircrews must train continuously to remain proficient. If a long period has elapsed
since the aviator's last night flight, he should perform simple maneuvers before
attempting more advanced maneuvers.
b. Because flight attitude references are limited at night, visual illusions,
disorientation, or vertigo may be induced. Aviators must be aware of these
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conditions and rely on their instruments to maintain a normal flight attitude.
When an unsafe condition develops while hovering, the aviator may turn on the
landing light or searchlight if environmental conditions permit.
c. Continuous observation outside the helicopter is required so that obstructions
and other aircraft are avoided. This is particularly true during multihelicopter and
terrain flight operations.
5-21. AIRSPACE MANAGEMENT
The increased emphasis on night operations has resulted in a greater number of missions
being flown at night. Aviators flying at night without lights have difficulty in visually
detecting aircraft being flown by aviators wearing I2 devices. Similarly, aviators using I2
devices report difficulty in seeing each other when they are engaged in different,
unrelated missions. The problem is compounded during field training exercises when
friendly and opposing forces are operating independently in the same airspace. Some
suggestions to help prevent night flight collisions are discussed below.
a. Sound operational planning and operating procedures must be developed and
practiced. This will prevent most airspace conflicts.
b. The area commander should establish priorities and guidelines for airspace
usage. These should be published in the SOPs and OPORDs with subsequent
changes disseminated as necessary. If an airspace conflict cannot be resolved by
established priorities, the commander will resolve it. His decision is based on the
mission, Threat capabilities, and support requirements.
(1) The commander may designate and authorize a representative to assign
airspace priorities for him. Also, the commander or his designated
representative should approve the use of airspace for preplanned
operations.
(2) The commander should authorize subordinate unit commanders--as
well as coordinators, controllers, and operators--to make on-the-spot
adjustments during airspace operations. This precludes unnecessary
hazards to friendly forces. Individual responsibilities are assigned and
stated in SOPs and OPLANs. Control rules and procedures and
communication instructions are also provided for in SOPs and OPLANs.
They should be exercised in the field before hostilities begin. Finally,
unaided and aided traffic will not be mixed in the same flight.
NOTE: When time or circumstances do not permit SOPs or command resolution of
conflicts, situations presenting immediate safety hazards will be resolved by the
coordinator or controller detecting the conflict.
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c. All airspace users (military intelligence, air defense artillery, Air Force, and
Army aviation units) participating in joint operations should have liaison elements
within the A2C2 system. The A2C2 system is linked to the ACA. The ACA is the
commander designated to assume overall responsibility for the joint airspace
control system. Normally, the ACA is the senior Air Force commander in the
theater of operations.
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CHAPTER 6
NIGHT TERRAIN FLIGHT
Detection avoidance is critical to the success of operations on any battlefield. Darkness
protects aircrews from visual and optical acquisition by the Threat. However, electronic
detection capability is not degraded by darkness. To avoid electronic detection by the
Threat at night, aircrews must conduct operations at terrain flight altitudes. The ability to
perform night terrain flight depends on the ambient light level, flight proficiency,
familiarity with the terrain, and availability of night vision devices. This chapter
discusses night terrain flight and the planning guidelines associated with it.
Section I
TERRAIN FLIGHT MODES AND COMMAND CONSIDERATIONS
6-1. TERRAIN FLIGHT MODES
a. Terrain flight is a tactical method of employing aircraft. It takes advantage of
terrain, vegetation, and man-made objects to degrade the Threat's ability to
visually, optically, thermally, or electronically detect or locate aircraft. Terrain
flight thereby enhances survivability. Aviators must remain constantly aware of
the capabilities and location of Threat weapons relative to available masking
terrain features and flight routes.
b. Terrain flight has proved effective in armed conflicts. It includes the tactical
application of low-level, contour, and NOE flight techniques. Figure 6-1
illustrates terrain flight modes.
c. The flight mode used depends on the factors of METT-T. Because extensive
night combat operations are expected in future conflicts, all Army aviators must
be proficient in night low-level, contour, and NOE flight. Of these modes of
terrain flight, NOE is the most difficult. Aided night flight airspeed limitations are
published in the appropriate ATM. These limitations are maximum airspeeds
based on high ambient light levels and clear weather conditions. Under low
ambient light or poor weather conditions, the lack of visual acuity may require
reduced airspeeds and altitudes to avoid obstacles and other aircraft. Unaided
night flight below low-level flight altitudes is discouraged.
6-2. COMMAND CONSIDERATIONS
Commanders must fully understand the limitations and requirements of night terrain
flight operations. The success of any night operation depends on the amount and quality
of preparation and training done before the mission. Night operations require extensive
training and the commander's maximum support and attention.
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Figure 6-1. Terrain flight modes
a. Commanders must establish and support night training programs. The training
must be realistic and designed around the proficiency and experience of the unit
in night operations.
(1) Crew endurance. Night flight training programs are degraded when
crew members are required to simultaneously perform day and night
duties. Because night terrain flight is more fatiguing than day flight,
commanders must ensure that crew members are given ample opportunity
to rest. Commanders must design and establish a crew endurance program
tailored to their unit's mission and include it in the unit SOP. When
scheduling night terrain flights, commanders should consider limiting
aircrew work load to night flights only.
(2) Aircraft maintenance. Aircraft maintenance requirements for day and
night flights are greater than those for day operations only. To allow
enough time for maintenance, commanders should decrease day
operations when night flights are scheduled. Maintenance personnel may
have to be divided into two shifts to support overlapping day and night
operations. These personnel must also be provided adequate time to rest.
(3) Safety. Commanders should be alert to signs of fatigue,
overconfidence, or carelessness in personnel engaged in night operations.
A carefully planned and executed night flight safety awareness program is
essential for accident-free operations. Commanders must ensure that
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leaders at all echelons emphasize and enforce the spirit, as well as the
standards, of the flight safety program.
(4) Environment. Commanders must ensure that proper facilities are
available for night training. Without a suitable training environment, the
ability of aircrews to perform safe night flights will be degraded.
b. Until the entire unit is fully trained in all aspects of night missions,
commanders may consider dedicating a platoon, troop, or company to tactical
night operations. Once established and proficient, this element can assist in
training the rest of the unit.
c. Since the introduction of night vision devices, many units have established
aggressive training programs for aided night flight. Their experience has shown
that terrain flight missions at night are more effective under all ambient light
levels when aircrews use night vision devices. Individual and unit training should
begin at the simplest level and progressively increase in difficulty. Until aircrews
become proficient in individual skills, they should not attempt complex
maneuvers and missions such as multihelicopter operations.
Section II
PLANNING GUIDELINES
6-3. GENERAL CONSIDERATIONS
a. Psychological and Physiological Stress. The knowledge that darkness makes it
difficult to see obstructions along the flight path causes stress. Stress, in turn,
causes fatigue. Fatigue impairs judgment, slows reaction time, and degrades flight
proficiency. As personnel gain experience in night terrain flight, however, they
will feel more confident and less anxious. Continuous flight training and proper
personal preparation enable aircrews to cope with the stress of night terrain flight.
b. Navigation.
(1) Navigation is a difficult task to perform at night at terrain flight
altitudes because the distance at which an object can be seen is reduced.
Even though airspeeds are slower at terrain flight altitudes, ground speed
appears faster. Navigation at night demands considerable attention in
premission planning. Navigational aids are generally unavailable, and
those that are available are often unreliable in tactical terrain flight modes.
Therefore, aircrews must be proficient in pilotage and dead-reckoning
navigation. To ensure accurate navigation, aircrews must be able to
identify man-made or natural features. Detailed planning and teamwork
are key to mission success.
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(2) Terrain flight requires aircrews to be proficient in terrain-map
correlation, map reading, map preparation, and terrain interpretation. It
also requires continual visual search for terrain features and checkpoint
acquisition. Aircrews must understand the effects of surrounding terrain,
ambient light, shadows, and seasonal changes in vegetation.
(a) NOE flight. Continual, detailed orientation is required during
NOE navigation. To remain continually oriented, both the PC and
navigator must associate features depicted on the map with actual
terrain features along the route.
(b) Contour flight. Contour flight is more direct, uses higher
airspeeds, and uses the contours of the earth for cover and
concealment. Checkpoints along the route are spaced according to
the speed to be flown. The navigator must give the PC airspeed
information so the aircrew can cross the checkpoints on schedule.
(c) Low-level flight. Low-level flight is generally carried out above
obstacles but at an altitude where detection by the Threat is
avoided or reduced. It is usually performed at a constant altitude
and airspeed. The generally higher airspeeds in the low-level
terrain flight mode require constant attention on the part of the
navigator to ensure all checkpoints are noted.
(3) Aircrews can use computed times, distances, and headings in both lowlevel and contour flight modes. In all modes of terrain flight, aircrews
should use pilotage as the primary means of navigation.
(4) If an aviator becomes disoriented during the flight, he must take
appropriate action to reorient himself. The first step is to locate and
identify a prominent feature in the immediate area. If this is not practical,
the aviator should attempt to return to the last positive fix and begin again.
The aircrew should use all available navigation equipment for orientation,
to include VOR, NDB, and doppler equipment and ATC facilities.
c. Radio Communication. At terrain flight altitudes, air-to-ground communication
is usually impossible because of masking between the helicopter and the ground
station. As a result, radios that require line-of-sight propagation (FM, VHF, and
UHF) become unreliable. Variations in sky waves can cause erratic operations.
Aircrews can identify the best radio communication points by constructing a
terrain profile. They can then transmit the prearranged signals as the aircraft
passes these points. Detailed planning ensures that aircrews can accomplish the
mission without radio communication with the ground station. Visual
communication signals must be established as a part of the unit's SOP. This
allows the AMC to control the flight when radio silence is required.
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d. Battlefield Light Sources. In combat the Threat may use high-intensity lights to
illuminate aircraft. Fires, flares, and weapon flashes are also battlefield light
sources. Aircrews should avoid viewing these light sources directly. Normally,
exposure to a light source does not affect all crew members the same way. If the
flight consists of two aviators, the one who is least affected by the light should
take control of the aircraft. Light sources can seriously degrade a crew member's
ability to see while using a night vision device. Crew members must be prepared
at all times for a light-induced I2 device failure. (Chapter 1 contains a detailed
discussion of night vision.)
e. Obstructions.
(1) Man-made.
(a) Wires and other man-made obstructions are difficult to detect at
night. Reducing airspeed allows aircrews more time to detect wires
and to take corrective action. Aircrews can identify wires by
associating them with man-made features. Long linear openings in
a wooded area may represent wire locations; poles also indicate the
presence of wires. Wires are usually present in open areas near
buildings. Because trees normally are higher than wires, aircraft
are less likely to hit wires over a forested area. Transmission lines
suspended on steel structures pose the highest wire obstacles.
Knowing the location of man-made obstructions ahead of time is
essential; knowing the position of the aircraft at all times is equally
important. Information about obstructions must be plotted on a
hazard map and made available to aircrews for use in planning a
night terrain flight.
NOTE: Wires are nearly invisible with AN/PVS-5A devices and may be only minimally
visible during high ambient light levels with other night vision devices.
(b) During night terrain flight, helicopters are particularly
vulnerable to blade strikes at low altitudes. The areas where
aircrews perform maneuvers at night should be larger than those
they use during the day. Other crew members must assist the
aviator on the controls by continuously advising him of the
helicopter's position in relation to obstacles. All crew members
required for a mission should wear I2 devices. Crew members not
on the controls should position themselves so that they can assist
the aviator in obstacle avoidance and aircraft separation.
(2) Natural. Birds are a hazard to night terrain flight. If a flock of birds is
encountered, the aviator should not make an abrupt change in heading. An
abrupt change in heading may cause contact with terrain obstacles, or it
may induce vertigo because of the sudden change in attitude. Because
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birds tend to disperse laterally with little ascent, the aviator should
maintain a straight-ahead climb to clear them.
f. Terrain. Ease of navigation depends on the vegetation, terrain relief, and terrain
features in the area. An aviator flying over a desert may not be able to judge
distances and altitude because of a lack of depth perception and the scarcity of
terrain features. Cultivated fields aid in navigation. The seasons also have an
impact on navigation. (Chapter 4 contains a detailed discussion on terrain
features.)
g. En Route Data. The altitude and airspeed depend on the Threat, terrain,
illumination, contrast, visibility, and weather. The aircrew must evaluate these
factors to determine whether to fly at altitude (above 200 feet), low level, contour,
or NOE. The aviator should fly slower when visibility decreases to prevent
inadvertent entry into IMC.
h. Altitude Changes. Descents should be gradual at night because estimating
altitude above terrain features during the descent is difficult. The aviator should
avoid rapid flight altitude changes to initiate descents, climbs, or turns or to adjust
airspeed. Rapid changes in flight altitude degrade the aviator's viewing
perspective outside the aircraft and may induce vertigo.
WARNING
Aviators must use care when descending into areas of limited contrast
during periods of low illumination.
6-4. COCKPIT TEAMWORK AND COORDINATION
a. Cockpit teamwork is critical for successful tactical night operations. Teamwork
effectiveness is improved by training and practice. Teamwork training develops a
close working relationship among crew members and prevents confusion and
reduces unnecessary communication. To improve crew proficiency, commanders
should attempt to maintain crew integrity. All crew members must be adequately
trained in the use of night vision devices according to the appropriate ATM and
unit SOP.
b. Crew members involved in night tactical operations must be trained and
proficient in blind cockpit drills. Crew members can thus spend more time on
navigation, hazard avoidance, and reconnaissance and less time to scanning inside
the cockpit. Crew members must know the location and operation of all systems
and switches in the aircraft. Emphasis must be placed on immediate-action
emergency procedures.
c. Before a night mission, all crew members must know their in-flight
responsibilities and duties. To avoid misunderstandings in the aircraft during a
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mission, crew briefings and "brief-backs" should be conducted before the mission.
Rehearsals should consider all possible situations that the aircrew may encounter
during the mission. These include Threat countermeasures, weather,
disorientation procedures, and navigation techniques and procedures.
6-5. AIRCRAFT PREPARATION AND EQUIPMENT
a. An aircrew should remove the doors on observation aircraft when
environmental conditions permit. This will permit the aircrew to have
unobstructed viewing during the terrain flight. The aircrew must carefully handle
and store the doors to avoid damaging the windows.
b. Radar altimeters are preferred for night terrain flight. This is especially true
during low light conditions and during flight over areas of limited contrast such as
water and deserts.
WARNING
Aviators should not rely on radar altimeters for obstacle avoidance.
Radar altimeters measure only obstacle clearance below the aircraft and
do not warn about clearance ahead of the aircraft.
6-6. MAPS AND VISUAL AIDS
a. Maps. During mission planning, the aircrew should assemble as many different
maps of the area as possible. The most commonly used maps are discussed below.
(1) The 1:250,000 map. The aviator can use the Joint Operations GraphicAir map when planning and flying the en route portion of the mission. The
JOG provides the aviator a relatively small map that is uncluttered by
unneeded information. It has latitude, longitude, and Universal Transverse
Mercator features. When prepared properly, the JOG map is compatible
with I2 systems. Aviators should consult the CHUM for the latest
information about a particular area.
(2) The 1:500,000 map. This map contains the tactical pilotage chart and
VFR sectionals. It is updated more often than the JOG map and provides
accurate information about major towers, beacons, and power lines.
(3) The 1:50,000 standard tactical map. The aircrew can use the standard
tactical map to locate and confirm unique map features and to transfer
them to the JOG. This map provides more detail of those areas that may be
difficult to interpret on the JOG. The aviator can accurately plot and study
en route landing or holding areas on this map. This map is also used for
the objective phase of the mission.
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NOTE 1: Aviators must be alert and cautious when switching from one map to another.
NOTE 2: Magnetic variation should be determined from the tactical map. Magnetic
variations on aeronautical charts are computed for normal flight altitudes, which could be
10,000 feet or higher.
b. Aerial Photographs. Aerial photographs, especially low-altitude oblique shots,
are useful in mission planning. Aviators should request photographs for at least
the objective area, the holding area, the ACP, and any portion of the flight route
or AO where the information differs between maps. Time and available assets
will determine whether aerial photographs are used.
c. Sand Tables and Terrain Boards. Sand tables and terrain boards are valuable for
night operations. If time permits, the aircrew should construct at least one table
for the AO and additional tables for the objective area and the en route portion of
the mission. Tables have value only if crew members pay close attention to detail
and accuracy.
6-7. GENERAL ROUTE AND AIR CONTROL POINT PLANNING
a. Route Planning. The navigation route to and from the objective area must be
tactically sound. It should not be so difficult that successful navigation is
impossible. Although missions differ in nature, some general rules for selecting
routes for unaided and aided night flights are helpful. When planning a flight, the
aircrew should-•
•
•
•
•
•
•
•
•
•
Avoid brightly lit areas, roads, and population centers.
Avoid planning the route near airports. (This will reduce the hazards associated
with other aviation operations and the possibility of radar detection.)
Avoid planning routes over large areas of low contrast such as large bodies of
water, large fields, desert areas, and snow-covered terrain.
Plan whether to negotiate large valleys and passes on the lighted side or the dark
(shadow) side. (This will depend on the Threat and the terrain.)
Avoid planning routes that head directly into a low-angle rising or setting moon.
(If there is no other choice, the aviator should plan to fly a zigzag route.)
Avoid planning route segments that require heading changes of more than 60 .
(This is especially critical during multihelicopter operations.)
Select intermediate reference points, in addition to checkpoints, along each leg of
the route for course confirmation and timing. (The lower the ambient light, the
greater the number of reference points that the aircrew should use.)
Plan to cross major roads and railroads at wide angles (for example, 90 ) to reduce
exposure time.
Maintain at least cruise airspeed to minimize exposure time in areas near
population centers or major roads.
Compute times, distances, and headings for the route, barriers, and prominent
map features. (This will aid the aviator in getting back on course if he misses an
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•
•
•
•
•
ACP or becomes disoriented. The aircrew should record the information on the
navigation map.)
Plot the times to cross prominent intersecting features such as roads, rivers, and
railroads. (This will make navigation easier.)
Anticipate wires near roads, towers, and buildings in open fields.
Plan alternate routes and bypasses in case the primary route is blocked by
weather, Threat forces, or other factors.
Minimize turns, ascents and descents, and airspeed changes during unaided or
aided multihelicopter operations. (Plans should include procedures to be followed
in case the lead is shot down. Plans should also include formation breakup and
join-up procedures.)
Conduct a map reconnaissance of the entire route to determine a safe en route
altitude.
b. ACP and Checkpoint Planning. After the aircrew crosses a general route to the
objective area, it should select ACPs and checkpoints along the route. (ACPs are
major planning points, while checkpoints between ACPs serve as aids to
navigation.) When selecting ACPs and checkpoints, the aircrew should carefully
study all available maps and photographs. The aircrew should--
•
•
•
•
•
•
•
•
•
•
•
Select checkpoints that are unique natural or man-made features and detectable
from a distance.
Choose checkpoints that contrast with the surrounding terrain.
Select ACPs and checkpoints away from towns. (The growth of towns may alter
ACPs and checkpoints or make their detection difficult.)
Select checkpoints away from bright lights.
Choose checkpoints that can be confirmed by an adjacent prominent feature along
the route. (This will alert aircrews that they are approaching the checkpoint.)
Select checkpoints at least 5 kilometers but not more than 20 kilometers apart.
Select checkpoints that have prominent barriers nearby. (A barrier is a prominent
feature which alerts the aircrew when it flies past a checkpoint. Major highways
and ridgelines are good examples of barriers. It is better to discard a good
checkpoint with no barrier in favor of a more difficult one with an excellent
barrier.)
Ensure the first and last checkpoints have easily identifiable features. (For
positive location and timing, the first checkpoint (start point) should be about 3 to
5 kilometers from the takeoff point and the last checkpoint (release point) should
be about 3 to 5 kilometers from the objective.)
Note the MSL altitude of each checkpoint. (This will aid in determining safe en
route altitudes.)
Select a checkpoint for the final approach leg of each intermediate landing area or
contingency LZ. (If possible, this checkpoint should enable the aviator to align the
aircraft with the landing direction to minimize maneuvering during the final
approach.)
Choose prominent terrain features as checkpoints when adverse environmental
conditions restrict visibility.
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•
Ensure checkpoints do not fall within the shadow cast by nearby terrain features.
6-8. AIDED NIGHT MISSION MAP PREPARATION
Map preparation for an aided night flight is critical to mission success. When preparing
the map, the aircrew should-•
•
•
•
•
•
•
•
Highlight or outline the proposed route and hazards to terrain flight with a
suitable pen.
Enter route and ACPs on the map first.
Include a distance up to 10 to 15 kilometers on either side of the planned route in
case the flight deviates from the planned course.
Mark lighted towers, beacons, cities, and other features on both sides of the
planned route.
Avoid overpreparing the map. (Only those features that are expected to be seen
should be marked. Trails, creeks, and dirt roads, for example, are not likely to be
seen; marking them would only clutter the map.)
Transfer key features from the 1:500,000 and 1:50,000 maps to the JOG map.
Avoid exaggerating map features.
Orient all notes and writing in the direction of flight for that particular leg.
6-9. AIDED NIGHT MISSION PLANNING AND BRIEFINGS
a. Planning Considerations.
(1) Each unit training mission, from planning to execution, should be as
realistic as possible. The commander designates the members of the
planning cell. When possible, they should be excused from other duties
and responsibilities during the planning phase. Members should direct
their full attention to planning the mission. The responsibilities of each
member must be clearly specified to avoid confusion and enhance
planning efficiency. All crew members should be involved in mission
planning.
(2) The aviator primarily responsible for navigation should make the final
selection of the flight route and checkpoints.
(3) Planners must draw all charts and diagrams to scale and construct them
as accurately as possible. Several cell members should double-check
times, distances, and headings. Aviators must study all times, distances,
headings, and estimated times of arrival.
(4) Planners should consider current mission profile requirements. They
should also consider worst-case situations such as adverse winds,
abnormal fuel consumption, enemy compromise, and downed aircraft.
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Planners should preselect and incorporate emergency LZs, holding areas,
downed crew rally points, and code names into contingency plans.
b. Briefing Considerations.
(1) The formal briefing must be conducted sufficiently in advance of the
scheduled departure to allow time to resolve problems raised during the
briefing. A final briefing should be scheduled just before the departure to
update weather, confirm the time schedule, and discuss any mission
changes. This also gives the AMC time to reemphasize important aspects
of the mission to the crew.
(2) All phases of the operation should be briefed in detail. Flight or team
leaders must hold individual flight briefings after the formal briefing. Each
crew member should be required to discuss the entire mission.
(3) Aircrews should conduct a final check of personal equipment as part of
the briefing. The aviation life support equipment officer and supply officer
should be present to correct any deficiencies.
6-10. ROUTE PLANNING CARDS
Route planning cards include the navigation card, en route card, and LZ or objective card.
Aircrews can use the symbols in Figure 6-2 to prepare route planning cards.
Figure 6-2. Route planning card symbols
a. Navigation Card. A navigation card may be constructed for long-distance
navigation. The card should include all essential information for the navigation
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portion of the mission. Figure 6-3 shows a sample navigation card. When
preparing a navigation card, the aircrew should-•
•
•
•
Use suitable ink that contrasts with the cards and is compatible with night vision
devices.
Make all letters and numbers at least 1/4 inch high.
Use these abbreviations or symbols: Heading (hdg), nautical mile (NM), degrees (
), feet ('), and knots (kt).
Use the remarks column to describe the appropriate checkpoint and other
pertinent information.
b. En Route Card. The aircrew may use an en route card to reinforce a map
reconnaissance. En route cards should display all essential information for each
phase of the flight or mission. A card may be constructed for each leg of the flight
and for each LZ, AO, objective area, FARP, holding area, and takeoff point. En
route cards should be as accurate as possible. A dark (black) card with white or
silver lettering is particularly effective. Figure 6-4 shows a sample en route card.
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Figure 6-3. Sample navigation card
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Figure 6-4. Sample en route card
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c. Landing Zone or Objective Card. The aircrew may use an LZ or objective card
to reinforce a map reconnaissance. An illustrated LZ or objective card can provide
a graphic picture of the landing area. Figure 6-5 shows a sample LZ or objective
card. When preparing an LZ or objective card, the aircrew should-•
•
•
Depict the size of the LZ or objective area, landing and takeoff headings, and
hazards in the area.
Ensure the card is as accurate as possible.
Use the standard symbols shown in Figure 6-2.
Figure 6-5. Sample LZ or objective card
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CHAPTER 7
MULTIHELICOPTER OPERATIONS
This chapter implements portions of STANAG 3627 (Edition One) and AIR STD
44/34B.
A formation is a flight in which two or more aircraft are in such proximity to each other
that any movement of the lead aircraft must be duplicated by the others. A
multihelicopter operation is the movement of two or more aircraft in one or more
formations. Multihelicopter operations concentrate maximum combat power and
maintain unit integrity. They reduce aircraft exposure time, giving the Threat less time to
react. They also facilitate security and control requirements. In addition, multihelicopter
operations provide a means to rapidly deliver and place a maximum number of troops on
the ground in the shortest possible time. The factors of METT-T determine the type of
formation used for a particular mission.
Section I
CONSIDERATIONS AND RESPONSIBILITIES
7-1. PLANNING CONSIDERATIONS
a. Mission. Mission considerations include the mission of the supported ground
unit and the mission of the supporting aviation unit.
b. Enemy. Enemy considerations include the-•
•
•
Current enemy situation.
Enemy's antiaircraft and ADA capability.
Enemy's visual or electronic surveillance capability.
c. Fire Support Plan. Fire support plan considerations include the--
•
•
•
•
Naval gunfire available.
Artillery support available.
Landing zone preparation plan.
Air support availability and requirements, including the type of aircraft and
ordnance.
d. Ordnance. Ordnance considerations include the type of ordnance to be used for
neutralizing fires.
e. Terrain and Weather. Terrain and weather considerations include the--
7-1
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•
•
•
•
•
•
Winds and turbulence.
Ceiling and visibility.
Size, shape, and surface of the LZ.
Ambient light levels throughout the mission.
Obstacles in or affecting approaches to the LZ.
Configuration of en route obstacles or corridors.
f. Formation Maneuver and Flexibility. Formation maneuver and flexibility
considerations include possible changes in the mission or the situation and
evasive tactics to be used.
g. Armed Aerial Escort. Armed aerial escort considerations include the number
and type of armed escort aircraft required and the number and type available.
h. Formation Control. Formation control considerations include the degree of
control required and the method of control such as radio, visual signals, and
prearranged timing.
i. Other. Other considerations include the--
•
•
•
•
•
Type of aircraft.
Type of night vision devices.
OPSEC and safety measures required.
Level of crew training and experience.
Aircraft capabilities and compatibility with night vision devices.
7-2. SUPPORTED GROUND UNIT COMMANDER RESPONSIBILITIES
The supported ground unit commander should brief the supporting aviation unit
commander. As a minimum, the briefing should include the-•
•
•
•
•
•
•
•
•
•
•
•
Rules of engagement.
Frequencies and call signs.
Number of troops to be lifted.
Disposition of friendly troops.
Desired arrival time in the LZ.
Safe routes (if known) to and from the LZ.
Fire and electronic warfare support plans.
Description, amount, size, and weight of cargo.
Control provided for aircraft in the PZs and LZs.
Location of the ground unit commander (if airborne).
Location and description of primary and alternate PZs and LZs.
Specific landing points in the LZ and desired pickup and landing formations.
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7-3. AIR MISSION OR FLIGHT COMMANDER RESPONSIBILITIES
The air mission or flight commander is responsible for effecting liaison with the
supported ground unit and supporting aviation units. Unit personnel must be briefed
before they begin a multihelicopter operation.
a. As a minimum, the supported ground unit briefing should include the-•
•
•
•
•
•
•
Safety requirements.
Use of aircraft lights.
Frequencies and call signs.
Probable en route formations.
Aircraft troop and cargo load capability.
Downed crew pickup points and downed aircraft procedures.
LZ or PZ lighting requirements and aircraft separation requirements.
b. As a minimum, the supporting aviation unit briefing should include the--
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Time schedule.
Rules of engagement.
Details about the LZ.
Formations to be used.
Use of aircraft lights.
Location of the commander.
Inadvertent IMC procedures.
Emergency breakup procedures.
Emergency medical facilities.
Method of changing formations.
Status of armed escort aircraft.
Rendezvous and join-up procedures.
Angular relationship of helicopters.
Troop load and allowable cargo load.
Refueling and rearming instructions.
Safety issues and signal requirements.
Horizontal distance and vertical separation.
Available intelligence concerning the routes and LZs.
Lost communication procedures (if different from SOP).
Downed crew pickup points and downed aircraft procedures.
Number of helicopters required for the mission and numbering system of
helicopters in formation.
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Section II
NIGHT FLIGHT FORMATIONS
7-4. AIRCRAFT SEPARATION
Aircrews flying in formation at night must be concerned with both the horizontal distance
and the vertical separation of their aircraft. These are addressed on the next page.
a. Horizontal Distance. Horizontal distance is measured in rotor-disk diameters.
At night, minimum separation is three rotor-disk diameters, measured between the
tip-path planes. The two types of horizontal separation at night are close and
extended.
(1) Close. The distance at night is normally three to five rotor- disk
diameters.
(2) Extended. The extended distance is based on tactical requirements and
can be any distance between helicopters that exceeds five rotor disks.
b. Vertical Separation. The types of vertical separation at night are flat and
stepped-up.
(1) Flat. All helicopters or all formations are flown at the same altitude.
(2) Stepped-up. The wingman and the section or element leader are
separated vertically by 1 to 10 feet, measured from the altitude of the
leader upward to the altitude of the wingman.
7-5. NIGHT FORMATIONS
Formations suited for night multihelicopter operations are echelon, straight trail, and
staggered trail. TC 1-201 discusses all types of formations in detail.
a. Echelon Formation (Right or Left). The lead directs the echelon formation to
fly either to the right or left. Each succeeding aircraft flies 30 to 45 astern of
the aircraft in front of it. Aircraft lighting configuration dictates the best
relative angle between the aircraft. All aircraft are echeloned on the same side.
In close formation, each succeeding aircraft maintains a separation of three to
five rotor-disk diameters and a vertical step-up of 1 to 10 feet. Echelon left is
shown in Figure 7-1, and echelon right is shown in Figure 7-2. Except during
takeoffs and landings, echelon formations (aided) may only be used at night at
altitude (above 200 feet AHO) and for low-level flight (200 feet AHO to 100
feet AHO). The echelon formation—
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•
•
•
•
Allows rapid deployment of troops to the flank.
Requires a relatively long and wide landing area.
Presents some difficulty in pre-positioning loads.
Allows unrestricted suppressive fire by door gunners.
Figure 7-1. Echelon left
Figure 7-2. Echelon right
b. Trail Formation. In a trail formation, all aircraft are in single file, each directly
behind the other. In a close trail formation, the number 2 helicopter (Chalk 2)
takes a position a minimum of three to five rotor-disk diameters directly behind
the lead aircraft with a 1- to 10-foot vertical step-up. Each trailing helicopter
holds the same relative position on the aircraft immediately to its front. This
formation is not limited to a prescribed number of aircraft. Helicopters are
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numbered and spaced, as shown in Figure 7-3. Except during takeoffs or landings,
aircrews using night vision devices may not fly trail formations at contour or
NOE altitudes. The trail formation-•
•
•
•
Simplifies the pre-positioning of loads.
Requires a relatively long landing area.
Allows rapid deployment of troops to the flanks.
Allows unrestricted suppressive fire by door gunners.
NOTE: At night, straight trail is the least desirable formation during periods of low light
levels. Aircraft attitude changes are extremely difficult for aviators to detect and react to
in this formation. A staggered or an echelon formation provides more flight cues.
Figure 7-3. Trail formation
c. Staggered Trail Formation. In the staggered trail formation, all aircraft are
alternately staggered behind the lead aircraft. Each aircraft holds a position 30 to
45 astern of the aircraft immediately to its front, alternating left and right
echelons. Each succeeding aircraft maintains a 1- to 10-foot vertical separation
from its lead aircraft. This formation is not limited to any prescribed number of
aircraft. Its size is dictated by mission requirements. Figure 7-4 shows a diagram
of the staggered trail positions. Except during takeoffs and landings, aircrews
using night vision devices will not fly staggered trail at contour or NOE altitudes.
The staggered trail formation-•
•
•
•
Simplifies the pre-positioning of loads.
Requires a relatively long and wide landing area.
Restricts the door gunner's suppressive fire somewhat.
Allows rapid deployment of troops for all-round security.
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Figure 7-4. Staggered trail formation
7-6. BASIC NIGHT FORMATION CONSIDERATIONS
a. Careful planning before conducting unaided or aided night multihelicopter
operations is essential to the safe, efficient control and maneuver of any size
formation. Safe and orderly formation flight is the result of extensive training,
continuous practice, and a high degree of air discipline.
b. A problem encountered during all night multihelicopter operations is fixation.
Fixation occurs when the aviator looks or stares too long or too hard at a point.
When experiencing fixation, the aviator may be unaware of the relative motion of
his aircraft in relation to the aircraft on which he is flying formation. To avoid this
fixation, the aviator must look around and move his eyes in a scanning pattern.
c. During unaided or aided night flight, depth perception is greatly reduced. For
this reason, all turns made by the lead aircraft should be constant rate and not
exceed a half standard-rate turn. The reduced degree of bank requires a larger
turning radius and must be considered during mission planning. Should a greater
than half standard-rate turn be necessary, the lead should slowly increase the
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degree of bank until he establishes the desired turn rate. By slowly increasing the
degree of bank, the lead aircraft will allow the wingman time to react. During a
turn, the inside wingman will have to decelerate slightly and drop slightly lower
than the lead aircraft. The outside wingman will have to accelerate and climb
slightly to maintain his relative position in the formation. Aircrews should avoid
planning route segments that require heading changes of more than 60 .
d. Altitude and airspeed changes should be smooth and gradual. This will allow
all aircraft in the formation to react in unison. Abrupt changes in airspeed and
altitude by the lead aircraft may cause an "accordion effect." This results when all
remaining aircraft in the formation make correspondingly abrupt airspeed and
altitude changes to maintain their relative position. These abrupt changes are
magnified by each succeeding aircraft toward the rear of the formation. Rates of
closure are particularly difficult to estimate at night. Aircraft toward the rear of a
formation may experience excessive rates of closure as they attempt to maintain
their relative positions. To avoid this, all aircraft, particularly the lead, must make
airspeed and altitude changes smoothly and slowly.
7-7. FORMATION TAKEOFF
A night formation takeoff is similar to a day formation takeoff. Most formation takeoffs
are made from the ground. All aircraft must lift off the ground simultaneously at a
prearranged signal. The initial rate of climb should be sufficient to clear barriers with a
margin for safety. Trailing aircraft should attain stepped-up vertical separation as soon as
possible after takeoff to permit acceleration and climb in clean, undisturbed air. Once the
flight is joined, the lead aircraft can slowly and smoothly accelerate to normal climb or
cruise airspeed.
7-8. LEAD CHANGES
a. Lead changes are inherently difficult. When possible, they should be made on
the ground. A lead change is never initiated, unaided or aided, by executing an
acceleration to overtake the lead aircraft. Only the lead aircraft may give the
signal to initiate lead changes.
b. The lead change will be conducted as prescribed in the prebriefing. Chalk 2
acknowledges the signal to change leads. The lead aircraft makes a heading
change of 30 to 90 and departs the formation. He maneuvers his aircraft a
minimum of an additional five rotor-disk diameters (minimum of eight rotor-disk
diameters) to the announced side (clear side). When Chalk 2 (new lead)
determines and announces that the former lead is clear of the formation, the
former lead visually confirms each aircraft as it passes. The former lead must not
drift too far from the formation when executing the turn away from the formation.
A good technique is for Chalk 2 to advise the lead when he has attained the proper
separation. At that time, the former lead should adjust his flight path to parallel
the formation. After the last aircraft in formation has passed, the former lead
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aircraft assumes the rear or the trail position with appropriate separation and
aircraft lighting.
7-9. FORMATION CHANGES
Formation changes in flight at night require a high degree of proficiency. Therefore,
changes from one formation to another should be executed only when tactically
necessary. Any changes to a formation should be specifically briefed and understood by
all crew members involved. All en route formation changes should first be made to the
trail formation and then to the desired formation.
7-10. RENDEZVOUS AND JOIN-UP PROCEDURES
A rendezvous is a prearranged meeting at a given time and place. It is a time from which
to begin an action or a phase of the operation or a place to return to after an operation.
Join-up is the bringing together of helicopters to establish a specific flight formation.
Rendezvous and join-up is the assembling and forming of aircraft into a specific flight
formation.
a. Ground. Judging rates of closure at night is inherently difficult. Therefore,
when the tactical situation permits, AMCs should consider conducting night
rendezvous and join-up on the ground at an intermediate rally point. Aircraft
conducting the rendezvous and join-up arrive at the rally point at prebriefed times
and from prebriefed directions. Once all aircraft are on the ground, they are
organized into a formation from which the mission is continued.
b. Air. For an airborne rendezvous, the flight lead approaches the rendezvous
point at the preplanned time and altitude. Upon reaching the point, he enters an
orbit in the prebriefed direction using a standard-rate (or less) turn and an airspeed
of 70 knots or as briefed. Joining members of the flight approach the lead by
entering his orbit at 70 to 80 knots or as prebriefed. As the final join-up is
completed, aircrews reduce airspeed and vary heading to close to the prebriefed
position on the lead aircraft. A safe rate of closure is essential during join-up. The
airspeed of the lead aircraft during the join-up is prebriefed but will not exceed 70
knots. The airspeed of join-up aircraft will not exceed 80 knots during the
maneuver. The rate of closure will not exceed 10 knots. Because the silhouette of
a helicopter cannot be seen except at a close distance, each aircrew must exercise
extreme caution to avoid overrunning the helicopter immediately ahead of it.
7-11. FORMATION BREAKUP
a. Breakup Into Single Aircraft (Method 1). This maneuver may be used when an
LZ is only large enough for one aircraft at a time. It may also be used for any
other reason that necessitates a formation breakup. Figure 7-5 shows an echelon
formation before breakup. In an echelon formation, the lead designates the
interval (normally 10 seconds) between breaks. Upon giving the command to
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execute, the lead turns 90 away from the wingman. He is followed 10 seconds
later by Chalk 2, 20 seconds later by Chalk 3, and so on. When this maneuver is
used for landing in a single-ship LZ, the formation ideally approaches the LZ on
the landing heading and starts the breakup over the LZ, as shown in Figure 7-6.
b. Breakup Into Single Aircraft (Method 2). This method of formation breakup
may be initiated anytime multihelicopter operations are terminated. The lead
gives the command to break up the formation. Upon receiving the command to
execute, the trail aircraft turns 30 to 90 away from the formation to the clear side.
Once the trail aircraft is visually confirmed clear, the remaining aircraft, in
reverse sequence, turn 30 to 90 away from the formation to the clear side. Once
clear of the formation, all aircraft adjust aircraft lighting as appropriate.
c. Breakup Into Two Aircraft Elements. This maneuver is executed from the
staggered-trail formation. The flight lead announces the time interval between
elements and receives an acknowledgement. Upon the lead's command to execute,
the first two aircraft continue on course. If load and flight conditions permit, the
aircraft increase airspeed by 10 knots. The remaining aircraft slow by pairs until
the desired separation is attained. Exterior lighting is adjusted as necessary.
Figure 7-5. Echelon formation before breakup
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Figure 7-6. Left break with 10-second interval for landing
7-12. FORMATION LANDING
During a formation landing, all aircraft touch down at the same time while maintaining
their relative positions within the formation. At night aircrews should avoid S-turns and
excessive maneuvering on the final approach. The lead must ensure that adequate
obstacle clearance and landing space are available for all aircraft in the formation. During
the approach, the lead maintains a constant approach angle. The rate of closure
throughout the approach and landing should be somewhat slower than a day formation
landing. This helps ensure that the rear element will avoid excessive maneuvering. If
continuing the approach is likely to result in an unsafe condition, the entire flight or
individual aircrews should execute a go-around.
7-13. VERTICAL HELICOPTER IFR RECOVERY PROCEDURES
Aircrews must be trained to cope with marginal weather conditions that they may
encounter during multihelicopter operations. If aircrews lose visual contact with other
aircraft and other outside visual references, they should use a standard formation breakup
procedure. This procedure should be covered in detail in the unit SOP and briefed before
each mission. Aircrews maintain communication with the flight lead to facilitate breakup.
They should make all climbs, turns, and descents at a predetermined standard rate. Each
aircrew should maintain the prescribed heading and altitude for at least 30 seconds after
the breakup. This ensures adequate separation before aircrews execute vertical helicopter
IFR recovery procedures. These procedures should be continually emphasized and
practiced during training.
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Section III
TACTICAL FORMATION FLIGHT
7-14. FREE-CRUISE TECHNIQUE
a. The flexibility required to conduct multihelicopter operations at lower terrain
flight altitudes is best achieved when aircrews use free-cruise formations with the
techniques of movement. (Techniques of movement are described in paragraph 715.) Aircrews must use free-cruise formations at contour (25 feet to 100 feet
AHO) and NOE (less than 25 feet AHO) altitudes. They should not exceed an
indicated airspeed of 70 knots for contour flight or 40 knots for NOE flight.
b. Free cruise is a technique that permits the wingman in a two-helicopter section
to freely maneuver a zone that extends 45 on either side and to the rear of the
lead's tail. Within the zone, the wingman may vary vertical separation, airspeed,
and distance from the lead. The distance the wingman trails the lead depends on
the visibility, ambient light levels, and range of organic weapons. However, it will
not be less than three rotor-disk diameters (unaided or aided). During free cruise,
the wingman must maintain visual contact with the lead without overtaking him.
The flexibility of free cruise enables the wingman to change his position behind
the lead at will and without radio communication. The wingman can choose his
own flight path to avoid obstacles, use terrain to maximum advantage, and orient
firepower toward known or suspected Threat positions. The section or element
and flight or division compose the flight organization.
(1) Section or element. The basic unit of the free-cruise formation is a
two-aircraft section or element. Figure 7-7 shows a free-cruise section. A
section consists of a flight lead and a wingman. The lead's primary
responsibility is to lead the element. In addition to making tactical
decisions, the lead is responsible for navigation. The wingman follows the
lead and maintains situational awareness at all times. The wingman must
monitor radio communication and know the flight's location at all times so
that he can assume the lead if necessary. For attack helicopters, the
wingman also protects and supports the lead aircraft.
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Figure 7-7. Free-cruise section
(2) Flight or division. A flight or division consists of two or more sections
or elements. Figure 7-8 shows a free-cruise flight consisting of three
sections. A flight lead has the same responsibilities as a section lead. The
lead of the second section is the alternate flight lead. He must maintain
situational awareness at all times and be prepared to assume flight lead
responsibilities. During the flight, the lead of the second section should
maintain visual contact with the wingman of the lead section.
7-13
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Figure 7-8. Free-cruise flight
7-15. MOVEMENT TECHNIQUES
The three methods of movement used during multihelicopter operations are traveling,
traveling overwatch, and bounding overwatch. TC 1-201 describes these techniques in
detail.
a. Traveling. Traveling is primarily used when enemy contact is not likely. The
traveling technique is used in low-level and contour flight. It is the fastest method
of moving a flight but provides the least security.
b. Traveling Overwatch. Traveling overwatch is used when enemy contact is
possible. It is characterized by continuous movement of the main element or the
lift elements. The overwatch elements (attack helicopters) move at variable
speeds and may even pause for short periods to take up attack positions at likely
ambush points. Traveling overwatch is normally used in contour flight.
c. Bounding Overwatch. Bounding overwatch is used when contact is likely and
the greatest degree of concealment is required. Elements move by bounds with
one element in position to observe, fire, or maneuver before the other element
moves. Overwatching elements cover the progress of bounding elements from a
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covered and concealed position offering observation and fields of fire. Bounding
overwatch is used in both contour and NOE flight.
7-16. CREW TEAMWORK
a. During aided night operations, the aviator on the controls should maintain
visual reference outside the aircraft at all times. He must be able to react quickly
to any movement from the aircraft on which he is flying formation. The aviator
should position his ICS selector so that he can rapidly respond on the internal
frequency used by the formation.
b. The aviator not on the controls should maintain both a visual scan of aircraft
instruments and outside references. He should inform the aviator on the controls
about any impending hazard. Additional duties are assigned during the mission
briefing.
c. During aided multihelicopter operations in UH-1 series, UH-60 series, and CH47 series aircraft, the two aviators flying the aircraft will be supplemented as
follows: UH-1 series and UH-60 series aircraft--one additional crew member
wearing an I2 device; and CH-47 series aircraft--two additional crew members
wearing I2 devices. Supplemental crew members position themselves in back to
observe the aircraft on which their aircraft is flying formation. However, in CH47 series aircraft, the second supplemental crew member monitors the opposite
side of the aircraft. These crew members assist in maintaining aircraft separation
and obstacle clearance. They are important members of the crew and must
participate to the fullest extent. Should the formation (UH-1 series and UH-60
series aircraft) require constant observation on both sides of the aircraft and the
additional crew member cannot position himself to observe both sides, two crew
members must position themselves in the back of the aircraft to provide
observation on both sides. One of these crew members (who observes the aircraft
on which his aircraft is flying) will use an I2 device, while the other crew member
may remain unaided. Other specific duties will be assigned during the unit's
mission briefings.
7-17. MIXED AIRCRAFT FORMATIONS
When different types of aircraft operate in a multihelicopter formation, the external
lighting capability of the different aircraft must be evaluated. Exterior lighting is not the
same for different types of aircraft such as scout and attack aircraft. Mission planners
must consider these lighting differences when planning multihelicopter operations with
different types of aircraft.
7-15
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CHAPTER 8
FIXED-WING NIGHT FLYING
Night flying is important in the training of a fixed-wing aviator. This chapter briefly
discusses night flying considerations and night takeoffs and landings. Practicing takeoffs
and landings under minimum lighting condi-tions will increase an aviator's night flying
proficiency.
8-1. PREPARATION
Crew members should be thoroughly familiar with the aircraft, its lighting system, and its
emergency equipment. A thorough preflight check of the aircraft and a review of aircraft
systems and emergency procedures are particu-larly important for night operations.
Because each aircraft has its own checklist, this paragraph does not address specific
points. Rather, it addresses general areas that should be included on any night preflight
check.
a. Lights Check.
(1) Aircraft lights should be turned on and checked for proper operation.
When possible, position lights should be checked for loose connections by
tapping the light fixture while the light is on. If tapping causes the lights to
blink, the cause must be determined and the deficiency corrected. A
flashlight should be kept within easy reach in case of lighting failure.
(2) Cockpit lights should be properly adjusted before takeoff. They should
be adjusted to the dimmest level that will allow the reading of instruments
and switches without hindering outside vision. The dimming of cockpit
lights will also eliminate light reflections on the windscreen and windows.
Position lights and anticollision lights should be turned on before starting
the engines and left on during engine operation.
b. Parking Ramp Check. The aviator should inspect the parking ramp before
entering the aircraft. Stepladders, chuckholes, and other obstructions are easy to
see during the day but difficult to see at night. A check of the area can prevent
taxiing mishaps.
8-2. TAXI, TAKEOFF, AND DEPARTURE CLIMB
The most significant difference between night and day flying is that fewer outside visual
references are available at night. Therefore, aviators must rely more on their flight
instruments at night for attitude control. This is particularly true for night takeoffs and
departure climbs.
8-1
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a. Taxi.
(1) Lights. The aviator should perform night taxiing slowly and with
extreme care. He should use the landing lights only as necessary for
clearing and orientation. Because landing lights may blind other aviators
approaching to land, the aviator should use taxi lights, when available,
instead of landing lights.
(2) Other aircraft. The aviator must use extreme caution when taxiing onto
an active runway for takeoff. Even at controlled airports, he should check
the final approach course for approaching aircraft. At uncontrolled
airports, the aviator should make a slow 360 turn in the same direction as
the flow of air traffic. This will enable him to identify other aircraft in the
vicinity.
(3) Alignment. After ensuring the final approach and runway are clear of
other air traffic, the aviator should align the aircraft with the runway
centerline. If the runway has no painted centerline, the aviator should align
the aircraft midway between and parallel to the runway edge lights. After
aligning the aircraft, the aviator should complete the lineup check.
b. Takeoff. As the aircraft accelerates, the aviator keeps it moving between and
parallel to the runway edge lights. It helps to look at the more distant runway
lights rather than at those close in and to the side. Night takeoff techniques are the
same as for normal daytime takeoffs, but the flight instruments should be more
closely monitored at night.
c. Departure Climb.
(1) The vertical velocity indicator should be checked to ensure that a climb
is indicated. A gradual, but continual, increase in the altimeter indication
should be noted. Figure 8-1 shows a 1,000 FPM rate of climb. Also, the
airspeed should continue to increase toward the best rate-of-climb
airspeed. After the aircraft becomes airborne, darkness often makes it
difficult to tell whether the aircraft is getting closer to or farther from the
ground. The aircraft must continue in a positive climb without settling
back to the runway.
(2) The attitude and heading indicators will provide the aviator visual
references while establishing the climb. No turn should be made until
maneuvering altitude is reached.
(3) The aviator should turn off the landing light after the climb is well
established and the light is no longer needed for visual identification and
collision avoidance. Although landing lights are useful during the take-off
roll, they become ineffective when the aircraft reaches an altitude where
8-2
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the light beam no longer extends to the ground. Also, the light can be
reflected by haze, smoke, or fog, thereby providing misleading
information.
(4) Fuel and engine gages should be checked often, and cockpit
illumination should be kept low. Other instruments should also be checked
regularly.
Figure 8-1. Positive climb
8-3. ORIENTATION AND NAVIGATION
On night flights, crew members must be particularly alert for other aircraft. The position
of the aircraft in relation to other aircraft can be recognized by the color combination of
their position lights.
a. Visibility. At night, clouds and restrictions to visibility may be difficult to see.
This is particularly true on dark nights or during over-cast conditions. Under
VFR, the aviator must avoid flying into clouds or a layer of fog. Usually, the first
indication of restricted visibility condi-tions is the gradual disappearance of lights
on the ground. If the lights begin to appear to be surrounded by a "cotton ball" or
glow, the aviator should avoid attempting further flight in that direction. If
descent through fog, smoke, or haze is necessary, horizontal visibility will be
considerably less than vertical visibility. Night VFR flight should be avoided
during poor or marginal weather conditions.
8-3
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b. Maneuvers. Night maneuvers should be practiced in designated areas or at least
in an area that is known to be comparatively free from other air traffic.
Proficiency in the required maneuvers will improve with practice.
c. Disorientation and Reorientation. Disorientation can happen to even the most
experienced crew member. Therefore, an orderly plan for reorientation should be
developed in advance. Thorough knowledge of the area, up-to- date navigation
charts, radio navigational aids, and assistance from ground radio stations and
other aircraft may be used to reestablish orientation.
d. Cross-Country Flights. Cross-country night flights present no particular
problem if preplanning is adequate. The same procedures should be followed at
night as during the day.
e. Overwater Flights. Crossing large bodies of water during night flights is
potentially hazardous. This is true not only from the standpoint of ditching, should
it become necessary, but also from the standpoint of aircraft control. The horizon
may blend with the water, making aircraft control difficult. Additionally, hazy
conditions over open water obscure the horizon and spatial disorientation may
occur. Even on clear nights, stars reflected on the surface may appear as a
continuous array of lights, making the horizon difficult to identify.
f. Illusions. Lighted runways, buildings, or other objects may cause illusions when
seen from different altitudes. From an altitude of 2,000 feet, a group of lights may
be seen individually. At 5,000 feet or higher, the same lights appear to be one
solid light mass. These illusions may become acute with altitude changes and, if
not overcome, could present problems when an aviator approaches lighted
runways.
8-4. APPROACHES AND LANDINGS
a. Factors.
(1) Distance. Distance may be difficult to judge at night. This is due to
limited lighting, lack of visual references on the ground, and the aviator's
inability to compare the size and location of ground objects. Altitude and
airspeed are also difficult to estimate at night. Therefore, the aviator must
closely monitor the flight instruments, particularly the altimeter and
airspeed indicator.
(2) Airspeed. Inexperienced aviators often tend to make night approaches
and landings at excessive airspeeds. However, every effort should be made
to execute the approach and landing using the same techniques that are
normally used during the day. It helps to constantly cross-check the
altimeter and airspeed indicator against the position of the aircraft
throughout the approach.
8-4
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(3) Depth perception. Even the most experienced aviators may err in depth
perception. Using power during the landing flare will reduce the rate of
descent and assist in maintaining a safe airspeed before touchdown. The
use of power is essential during landings to unlighted airfields when the
surface is not visible. This is also an effective technique to prevent errors
in judgment and perception even on lighted airfields. The best night
technique is to maintain a slight amount of power and airspeed above stall
until the wheels make ground contact.
b. Procedures.
(1) Approaching an airport. When approaching an airport, the aviator must
identify runway lights and other airport lighting as early as possible. If the
airport layout is unfamiliar, the aircrew may have difficulty sighting the
runway because of the maze of lights in the area. Figure 8-2 illustrates the
difficulty of sighting a runway surrounded by lights. Because airport
beacons are difficult to see when the aviator is directly overhead, he
should select the general area of the airfield by first locating the beacon.
Once the aircrew has located the area, the aviator should continue to fly
toward the location of the beacon until the aircrew can distinguish the
runway lights.
(2) Entering traffic. Once the aviator sees the runway lights, he should
keep the approach threshold lights in sight throughout the traffic pattern
and approach. He should fly the traffic pattern using the same techniques
that he uses during the day.
(3) Making the final approach. After turning onto the final approach and
aligning the aircraft midway between the runway edge lights, the aviator
should note and correct for wind drift. Throughout the final approach, the
aviator must coordinate power with pitch to accurately maintain the
airspeed and angle of descent. If the airfield has a VASI, the aviator can
use it to help maintain the proper approach angle. Figure 8-3 shows a
VASI.
(a) Obstruction lights. If obstruction lights are available, the
aviator can use them, along with the threshold lights, to establish a
sight picture during the landing approach.
(b) Runway lights or reference points. In the absence of
obstruction lights, runway lights aid the aviator in judging the
approach angle. They are especially helpful when the terrain is
level and the lights are spaced at a known interval. However,
uneven terrain or nonstandard light spacing makes the angular
reference unreliable. In such cases, the aviator should take
advantage of other reference points near the approach area.
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Figure 8-2. Light pattern for orientation
Figure 8-3. Visual approach slope indicator
(4) Executing the roundout. Inexperienced aviators may tend to round out
too high until they become familiar with the apparent height for the correct
roundout position. To aid in determining the proper roundout point, the
aviator should continue a constant approach descent until the landing light
reflects off the runway and tire marks or expansion joints on the runway
can be clearly seen. At that point, the aviator should smoothly start the
roundout for touchdown and continue to apply standard daytime
procedures outlined in the appropriate ATM. Figure 8-4 illustrates the
proper roundout point. During landings without landing lights or where
marks on the runway are not visible, the aviator should start the roundout
when the runway lights at the far end of the runway first appear to be
8-6
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rising higher than the aircraft. This demands a smooth and timely roundout
and requires that the aviator "feel" for the runway surface using power and
pitch changes, as necessary, for the aircraft to settle softly onto the
runway.
Figure 8-4. Roundout when tire marks are visible
8-7
TC 1-204
CHAPTER 9
DROP FLARE EMPLOYMENT
Night combat operations are essential to survival on the modern battlefield. Although
drop flares cannot be used on the high-intensity battlefield, they can be effectively used
where Threat weapons do not restrict flight altitude. Commanders of aviation units that
are capable of delivering flares must ensure aircrews are trained in the proper launching
techniques. This chapter provides a general description of the drop flare and discusses
procedures for preparing and launching it.
9-1. TARGET IDENTIFICATION
To engage targets at night, aircrews must be able to correctly identify the targets. To aid
in identifying targets at night, aircrews use artificial illumination or night vision devices.
Figure 9-1 shows target identification aids.
Figure 9-1. Target identification aids
9-2. DESCRIPTION
a. Characteristics. The current Mk 45 drop flare is an improved version of the Mk
Model O. It is known as the Mk 45 Model O with adapter and is shown in Figure
9-2.
9-1
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Figure 9-2. Characteristics of Mk 45 model O flare with adapter
b. Fuze Mechanism. Flare function is controlled by the fuze mechanism located
on the end of the flare. It consists of a yellow ejection dial indicator with 15
setting points, ranging from 500 to 14,000 feet. These settings correspond to the
distance the flare will fall from the helicopter before flare ignition. A safety pin is
inserted into the adapter. The pin should be removed only when the flare is
positioned in the M19 dispenser or readied for hand-launching. The safety pin
should be replaced if the flare is not used. TM 9-1370-201-12 contains a detailed
description of the internal component of the flare. Figure 9-3 shows the fuze for
the Mk 45 model O flare.
9-3. FUZE SETTING
The fuze dial indicator must be properly set to ensure maximum effectiveness of the drop
flare. Optimum ignition height is 2,500 feet AGL. Flare ignition above or below this
altitude will result in a loss of light intensity on the target area or a loss of burning time
and a smaller ground radius of illumination. Figure 9-4 illustrates how a fuze setting is
calculated. The proper fuze setting can be determined with either the bar graph or the
fuze-setting formula.
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Figure 9-3. Fuze for the Mk 45 Model O flare
Figure 9-4. Calculation of fuze setting
a. Bar Graph.
(1) To use the bar graph, the aviator must first know the altitude at which
he should fly the aircraft above the area to be illuminated. This can be
determined by referring to the tactical map and identifying the elevation of
the target area. The difference between the elevation of the target area and
the flight altitude is the altitude above ground level.
(2) The aviator should enter the graph along the horizontal line at the
appropriate altitude. He should then move vertically to the top of the bar.
The proper fuze setting is identified on the vertical scale to the left of the
bar. Figure 9-5 shows an example of how the bar graph is used to
determine the proper fuze setting.
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Figure 9-5. Bar graph
b. Formula.
(1) If the bar graph is not available, the proper setting can be easily
determined by using this formula: fuze setting = AGL - 2,500 feet.
(2) The computed fuze setting should be rounded off to the nearest 1,000
feet for flight above 3,000 feet AGL. For example, if the AGL is 5,200
feet, the computation is as follows: fuse setting = 5,200 - 2,500 = 2,700
feet. Rounded off to the nearest thousand, the fuse setting is 3,000 feet.
9-4. LAUNCH PROCEDURES
The Mk 45 flare may be launched from the M19 dispenser or with the M164 static line.
The specific procedures for each method are discussed below.
a. M19 Dispenser. The M19 flare dispenser is the preferred method for launching
Mk 45 flares. This system, which can store up to 24 flares, can be installed on any
of the UH-1 helicopters. The empty dispenser weighs 150 pounds; fully loaded, it
weighs 822 pounds. Incorporated into the system is an emergency feature that will
jettison both the dispenser and the flares from the helicopter. TM 9-1370-201-12
details procedures for installing and using the M19 dispenser. Figure 9-6 shows
the M19 flare dispenser.
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Figure 9-6. M19 flare dispenser loaded with flares and installed in UH-1
b. Hand-Launch. Some field units will not have the M19 flare dispenser.
Therefore, aircrews must know the procedures for launching drop flares by hand.
The M164 static line is the only equipment used when the flare is hand-launched.
Until a device for transporting flares externally is approved, flares will be carried
in the cabin section of the helicopter. The recommended procedure is to remove
the jump seats and raise the left troop seat. The flares should be stacked single file
along the left side of the cabin section with the fuze end toward the crew member
station. A tiedown is required to secure the flares to the floor. Figure 9-7 shows
flare loading procedures. The flares cannot be jettisoned in an emergency. A
recommended safety procedure is to fly with both cargo doors open. If a flare
functions inside the helicopter, the tiedown must be released and the flares kicked
or pushed out the open door.
9-5. FLIGHT PATTERN
To provide continuous illumination, the aviator establishes a flight pattern that will
position the aircraft over the drop point every 3 minutes. This will permit a 30-second
overlap between old flare burnout and new flare ignition. The aviator can position the
aircraft visually or by using radar or radio navigational aids. When dropping flares, the
aviator can use a racetrack or teardrop flight pattern. When using either of these patterns,
he must plan the approach leg to the drop point into the wind.
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Figure 9-7. Flare loading procedures
a. Racetrack Pattern. Immediately after flare release, the aviator executes a double
standard rate turn (about a 30 bank at 90 KIAS). He adjusts the time of the
outbound leg so that the total time of the outbound and inbound legs does not
exceed 2 minutes. Figure 9-8 illustrates the racetrack flight pattern.
Figure 9-8. Racetrack flight pattern
b. Teardrop Pattern. Immediately after flare release, the aviator turns 30 , either
left or right, to the inbound heading. He adjusts the outbound leg time so that the
total time of the outbound and inbound legs does not exceed 2 minutes. After the
time for the outbound leg has elapsed, the aviator establishes a turning rate to roll
out on the inbound heading after 1 minute. After passing the drop point, he
repeats the procedure. Figure 9-9 illustrates the teardrop flight pattern.
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Figure 9-9. Teardrop flight pattern
9-6. WIND-DRIFT CORRECTION
Until the parachute opens, wind effect on the flare is negligible. However, after the
parachute opens, the flare will drift at about the speed of the wind. To determine the
proper upwind correction for a crosswind, the aviator must know both the wind speed and
the direction at 2,500 feet. Normally, only forecasted wind conditions will be available.
Using the best available wind information, the aviator aligns the aircraft into the wind
and determines the drop point. As a rule of thumb, he should move the drop point 500
meters upwind for each 10 knots of wind. This will equally distribute the burning time of
the flare on the upwind and downwind sides of the area to be illuminated. After dropping
the first flare, the crew member launching the flares can make more accurate corrections
based on actual wind conditions. Adjustment by the ground observer also provides an
accurate means of positioning the flare over the target area.
9-7. LINEAR TARGET ILLUMINATION
A single flare may not produce enough light to illuminate an entire target area. Multiple
drop points may be required. When illuminating targets requiring more than one ignition
point, the aviator spaces the drop points 1,000 meters apart. Flying at 90 knots requires a
22-second interval between launches to achieve a 1,000-meter separation between flares.
When supporting other aircraft, such as attack helicopters, the aviator drops flares behind
and over the target area viewed by the attack helicopters. This will ensure proper
illumination and silhouetting of the target. Figure 9-10 illustrates the multiple drop
method.
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Figure 9-10. Illumination of targets requiring more than one ignition point
9-8. SAFETY CONSIDERATIONS
When dispensing flares, aircrews must use safe operating procedures. They should be
aware of and follow the safety considerations discussed below.
a. After the candle and parachute have been ejected, the outer container will
continue to free-fall and become a hazard to ground personnel. To avoid injuring
ground personnel during training missions, aircrews must not drop flares over
known friendly positions.
b. When moving around in the cabin or launching flares out the cargo door, the
crew member must wear a harness.
c. Debris blown from the flare at ignition may damage the aircraft if a flare, with a
fuze setting of 1,000 feet or less, is deployed at airspeeds below 70 knots.
d. When possible, the aircrew should not release a drop flare set to ignite below
2,300 feet AGL. Doing so does not allow for complete burnout and could create a
fire hazard on the ground.
e. The aircrew must stow flares in the aircraft so that they can be immediately
jettisoned in case of emergency or accidental fuze activation.
f. When using the M19 flare dispenser, the crew member releases flares one at a
time to prevent jamming in the snout and possible functioning onboard the
aircraft.
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g. The crew member dispensing the flares should wear asbestos gloves. If a flare
activates onboard the aircraft, the crew member can then dispose of the flare
without getting burned.
h. The PC should include information on in-flight emergencies during the
preflight briefing.
i. Each crew member must be familiar with the safety precautions discussed in
TM 9-1370-201-12 relating to the care and handling of flares.
9-9. TRAINING PROGRAM
The effectiveness of the training received will determine the effectiveness of combat
aerial flare illumination. Aviation unit commanders must ensure that training programs
are task-oriented and that crew members achieve the required degree of proficiency. To
assist the commander, a recommended training program for the Mk 45 Model O flare is
provided in Table 9-1.
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Table 9-1. Training program for the MK 45 Model O flare
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APPENDIX A
ELECTROMAGNETIC SPECTRUM
The electromagnetic energy spectrum includes the entire range of wavelengths or
frequencies of electromagnetic radiation. Gamma rays, X rays, ultraviolet, visible light,
infrared, microwaves, and radio waves are part of this spectrum. Night vision devices
make use of the visible light energy band and the infrared energy band. These bands
comprise a very small portion of the electromagnetic spectrum. Figure A-1 highlights the
portions of the electromagnetic spectrum used by night vision devices.
A-1. VISIBLE LIGHT
a. The human eye "sees" as a function of the amount of reflected visible light
sensed by it. The eye sees color as a result of the reflective or nonreflective
properties of the object being viewed. In other words, a leaf appears green
because it reflects mainly the green wavelength within the visible spectrum (about
0.52 to 0.57 micron) and absorbs most of the remainder.
b. For the leaf to reflect visible light energy, it must have energy in the
wavelengths between 0.4 to 0.7 micron incident upon it. During daylight, the
greatest source of visible light energy is the sun. The sun continuously emits this
energy and permits the eye to discriminate form and color. When the sun sets,
most naturally occurring visible light energy is reduced and normal eye function
makes the transition to scotopic vision which results in decreased visual acuity.
Scotopic vision requires either naturally occurring night light sources or artificial
lights. I2 systems amplify natural and artificial visible and near infrared energy.
A-2. INFRARED RADIATION
The sun emits energy across the entire electromagnetic spectrum, not just the visible light
spectrum. As infrared energy enters the atmosphere and penetrates to the surface, it is
reflected or absorbed to produce stimuli for night vision devices. Reflected infrared light
can be amplified by I2 devices. When infrared light is absorbed, temperature changes
occur in those natural and man-made substances in the environment. As the sun sets, the
effects of this solar heating remain. Thermal-imaging systems are effective because they
can detect this heat as it is radiated by the environment.
a. Infrared radiation exists because of molecular activity within elements of
substances. As molecules are stimulated, they vibrate. As molecules vibrate, they
radiate energy, including infrared energy. The stimulus for molecular activity is
heat. The intensity of molecular activity occurs in direct proportion to
temperature.
b. The temperature of an object is caused by natural or artificial thermal sources
or, in many cases, by a combination of the two. The amount of infrared energy
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radiated by an object depends on the amount of thermal energy the object is
exposed to and how much thermal energy it absorbs, reflects, or transmits
through.
Figure A-1. Electromagnetic spectrum
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APPENDIX B
I2 SYSTEM COUNTERWEIGHTS
The weight of I2 devices shifts the CG of the head and helmet system forward.
Attachment of a counterweight to the back of the helmet will balance the head and helmet
system. The counterweight system is designed to allow aviators to add sufficient weight
for individual comfort and alignment and reduce fatigue. The use of a counterweight is
not mandatory.
B-1. COUNTERWEIGHT SYSTEM
The counterweight system consists of two elements: the weight bag and the
counterweights. Both elements are discussed below.
a. Weight Bag. The weight bag can be locally constructed from Nomex fabric,
cloth, high temperature-resistant, nylon twill, shade OG 106, NSN 8305-00-9356443. The material is requisitioned by the yard. A closing flap for the weight bag
can be constructed with Velcro fastener loop tape, NSN 8315-00-450-9837, and
Velcro fastener tape nylon, NSN 8315-00-926-4930. Velcro fastener loop tape, 2
by 3 inches, is sewn on the rear of the weight bag for attachment of the bag to the
SPH-4 helmet. The weight bag must not bulge when the counterweight is placed
in it.
b. Counterweights. The ideal counterweight is buckshot placed in Ziploc pouches
and then placed in the weight bag. Buckshot makes the total weight of the
counterweight easily adjustable. It is also less of a missile hazard in a crash than a
one-piece weight. Tire weights should not be used because they have sharp edges
which reduce the life of the weight bag and are a potential missile hazard.
B-2. COUNTERWEIGHT MEASUREMENT
a. Amount. The recommended initial weight is 12 ounces for the AN/AVS-6, 18
ounces for the AN/PVS-5 series, and 22 ounces for the AN/PVS-5 series with full
faceplate and daylight filter. Individuals should add or remove weight to achieve
best balance and comfort.
b. Variables. Many variables affect the amount of weight needed to counterweight
an I2 system. Variables that have a minor effect include helmet size, head shape,
and helmet suspension type. The factors discussed below have a major effect on
the amount of counterweight required.
(1) The farther away from the eyes that the intensifier tubes are positioned,
the more counterweight required. Figure B-1 shows those factors that
affect counterweights.
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(2) Mounting the weight bag high on the Velcro strip on the back of the
helmet increases the counterweight required. The weight bag should be
attached low on the back of the helmet to achieve the least possible headsupported weight. If a dual battery pack is used, it should be mounted
above the weight bag.
(3) The flip-up feature of the GX-5 mount and the AN/AVS-6 mount
shifts the CG of the intensifier tubes forward and upward away from the
CG of the head and helmet system. This increases the amount of
counterweight required. The requirement for additional weight mitigates
the advantage of the flip-up feature to a certain extent, especially for the
GX-5. Use of the flip-up option may increase discomfort because of the
resultant out-of-balance condition. Therefore, aircrews should not use the
flip-up feature for extended periods.
Figure B-1. Factors affecting counterweights
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APPENDIX C
PNVS FLIR
This appendix discusses the general operational characteristics of the PNVS. It describes
the major components of the PNVS FLIR system and how they interface and operate as a
single system. The appendix also provides detailed instructions on how the aviator
prepares the system for use.
C-1. OPERATIONAL CHARACTERISTICS
a. Afocal Assembly.
(1) The term afocal assembly describes the combined effects of the shroud
window and the elevation mirror. The afocal assembly begins with the
germanium crystal window mounted on the PNVS turret shroud and
includes the gimbal-mounted elevation mirror. This assembly is critical to
system performance. The collection optics are afocal because rays from
the assembly must be collimated (parallel) at the scanner module. A scan
of converging or diverging rays would result in a curved focal plane. This
would degrade or distort the image away from the center axis. The afocal
design also reduces lens-to-lens reflections that can cause distortion. The
assembly performs entrance-aperture, definition-scene magnification and
defines the instantaneous FOV.
(2) The lens on the turret shroud is constructed of germanium crystal
because of germanium's favorable transmission properties of 8- to 14micron wavelength energy. While germanium allows this bandwidth of
energy to pass freely, it blocks or attenuates most other wavelengths of
electromagnetic energy. The germanium crystal lens is a semiconductor of
electricity. The lens heats up when electricity passes through it. AC
voltage directed through the shroud lens activates the anti-ice capability of
the PNVS. The shroud lens is coated on both sides to improve its
efficiency in collecting and transmitting infrared energy in the 7.5- to 12micron range. If the exterior coating wears away because of the abrasive
action of particles carried by the rotor wash, an observable degradation in
FLIR performance will result.
(3) The elevation mirror assembly is located immediately behind the
shroud lens. During normal system operation, this assembly enables the
operator to vary his viewing angle in the elevation axis without
compromising image quality. Although the elevation mirror moves in
response to the aviator's head movements, infrared energy is still directed
in a collimated pattern to the face of the scanner assembly. Figure C-1
shows the PNVS turret.
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Figure C-1. PNVS turret
b. Mechanical Scanner Module. The mechanical scanner is a two-axis gimbal and
housing assembly. A gimbal-mounted, two-sided, reflecting mirror is contained
within the module. It simultaneously sweeps infrared energy across the infrared
detector array and visual light from the LED array across the face of the EO Mux.
The continuous process which occurs between the scanner and the detector-dewar
module in the infrared path is explained below.
(1) A full FOV of infrared energy, as determined by the afocal assembly,
is incident upon the front side of the mirror at any given time. The
detectors, which are mounted in a narrow vertical row, cannot respond to
the entire FOV at the same time. The scanner mirror sweeps infrared
energy across the detectors at a rate that enables them to respond to all
energy in the viewed scene. To make this sweep, the mirror is electrically
driven through 10 of horizontal rotation where it stops. Return springs
cause rotation in the opposite direction back to the original position of the
mirror.
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(2) The detectors are separate and distinct. This means a physical
separation, though small, exists between them. As it sweeps, the mirror
performs an interlacing function to prevent a loss of infrared energy
between the detectors. When the mirror reaches its 10 limit in one
direction of its sweep, a solenoid is actuated. This causes the mirror to tilt,
just slightly, in the vertical plane. On the return sweep, the energy that was
between the detectors is now incident upon them and a complete infrared
energy FOV has been swept across the detectors. At the end of the return
sweep, another solenoid actuates the mirror, returning it to its original
vertical plane. Thus the process continues. This sweep-offset-sweep
motion occurs 30 times a second. Figure C-2 depicts a scene being viewed
by the sensor.
Figure C-2. Scene being viewed by sensor
c. Infrared Imager Module. The infrared imager module collimates infrared
energy from the mechanical scanner and folds it approximately 90 for entry into
the focus wedge assembly. The module contains a folding mirror and three
germanium crystal lens elements.
d. Infrared Focus Wedge Assembly. The infrared focus wedge assembly is
installed between the infrared imager and the detector-dewar module. This
assembly provides optimum infrared focusing at the detector-dewar aperture. A
drive motor, which shifts the physical position of two wedge-shaped lens
elements, is used for focus adjustment.
e. Detector-Dewar Module.
(1) The detector-dewar module performs an infrared-to-electrical
conversion function. It uses an array of 180 detectors (mercury-cadmiumtelluride) sensitive in the 7.5- to 12-micron region. As infrared energy
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contacts a detector, it causes electrical excitation and produces current
variation. This current variation becomes an electronic representation
(signal) of the infrared energy sensed by the infrared detector.
(2) The 180 detectors are mounted in a single vertical row on a strip that is
approximately 0.7-inch tall and 0.1-inch wide. This strip is mounted
behind an aperture in an insulated vacuum enclosure called a dewar. The
dewar contains the detector strip and the cold finger of the mechanical
cooler module. The detector strip is mounted to a bellows assembly that
serves as an extension of the cold finger. The cooler produces a
temperature of 80 K (-389 F) at the detector strip. This significantly
reduces detector electrical excitation as a result of electronic noise
generated from within the components of the modular FLIR. Noise
attenuation is also provided through the design and composition of the
aperture on the detector-dewar assembly. This subcomponent, properly
termed the dewar window, is a dielectric filter that restricts the passage of
wavelengths outside the range of 7.5 to 12 microns. The dewar performs a
dual function. It insulates the detectors to maintain the required low
operating temperature and minimizes the detection of background
radiation (noise and unwanted signals).
NOTE: Although 180 infrared detectors are incorporated in an infrared detector array,
only 170 to 172 detectors are actually used. This is because of limitations imposed by EO
Mux camera geometry and the desire to undersize the image-to-camera raster.
f. Cooler Module.
(1) The cooler module is a miniature, closed-cycle refrigerator that
operates on a thermodynamic basis known as the Stirling cycle. The
refrigerator extracts heat from the infrared detector array to establish and
maintain the required operating temperature of 80 K (-389 F).
(2) The cooler removes heat by the expansion of helium. Helium is
alternately compressed at ambient temperature and allowed to expand to
the required low temperature in two separate chambers within the cooler.
As the gas alternately compresses and expands, it moves through a
regenerator (serving as a heat exchanger), which draws the heat out of the
gas. The expansion chamber extends into the cold finger, which permits
temperature reduction at the detector strip. The cold finger is thermally
linked to the detector strip by a nickel-copper expansion bellows. An outof-phase motion of two pistons within the cooler assembly causes the gas
to compress and expand. An eccentric drive mechanism, which is powered
by an electric motor, drives the pistons. Heat from the compression
process is removed through fins attached to the cooler housing and by
conduction through the compression head. The detector elements and the
cold finger are contained in an evacuated dewar to minimize heat loss.
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g. Preamplifier Module. The preamplifier module amplifies low-level signals
from the photoconductive detectors. Because each detector must have a separate
electrical path to its companion LED in the LED array, 180 channels are provided
in the preamplifier section. This is accomplished through the use of nine 20channel amplifier cards.
h. Postamplifier Module. The postamplifier module amplifies the signals from the
preamplifier module to a level sufficient to drive the LEDs in the LED array. As
in the case of the preamplifier module, the postamplifier provides 180 separate
channels by using nine 20-channel amplifier cards. It also accepts operator inputs
necessary to control FLIR polarity (white hot or black hot) and FLIR level and
gain adjustments.
i. LED Module. The LED array converts an electronic signal, corresponding to
the infrared signal, into visible light energy. The LED array contains 180 galliumarsenide-phosphoride diodes arranged in a format which matches that of the
infrared detector array. Each LED element position has a corresponding detector
element position. Channel outputs of the postamplifier section drive the LEDs.
The visible light formed by the LEDs constitutes the image or picture of the
viewed scene. The LEDs, in concert with the visual collimator-mechanical
scanner interface, provide the image to the EO Mux for remote transmission to the
display device. If the EO Mux is removed, an individual looking into the
mechanical scanner aperture would see a full FOV image of the scene.
j. Visual Collimator Module. The visual collimator module collects light from the
LED array and projects collimated light onto the mechanical scanner. The
collimator consists of eight optical elements and a folding mirror. The collimator's
function is to transfer, with minimal distortion, the visible light output from the
LEDs to the EO Mux by way of the scanner. The lens elements and fixed,
nonadjustable focal length perform this task by maintaining light energy in a
parallel or collimated format.
k. Optical Relay Tube. The optical relay tube is located between the scanner
assembly and the EO Mux. It directs visible light from the scanner into the lens of
the EO Mux.
l. EO Mux. The EO Mux converts the visual light image produced by the LED
into electronic video signals for remote transmission to a display device. The EO
Mux in the modular FLIR is a vidicon, silicon TV camera. It takes a full-frame
picture of the visual light information on the mechanical scanner 30 times a
second. This rate coincides with the interlacing of two, 180-line fields of
information from the LED array to form a 360-line, full-frame image 30 times a
second. The picture that the EO Mux produces from the 360-line visual image is
formatted into 875 lines. This approach maximizes the resolution or clarity of the
display viewed by the operator because each detector or LED signal depicts
approximately three lines of the final display. For example, the rates of 875 to 360
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equal 2.5 to 1. (A standard TV camera uses a 525-line format and lacks the detail
required for terrain flight or targeting applications.) The 875-line rate of this
camera requires that PNVS videotapes be viewed on specialized video equipment.
m. Scan and Interlace Module. The scan and interlace module provides the
electrical signals to drive the mechanical scanner module. It provides scan mirror
frequency and position control, interlace solenoid drive, video gate signals, and
mechanical failure detection. The module interfaces with, and is controlled by, the
EO Mux. In this way, the scan-interlace module ensures that the scanner is in
frame synchronization with the EO Mux.
n. Bias Regulator Module. The bias regulator module supplies a low-noise
regulated voltage to the detectors located within the detector-dewar module. This
low-level current balances the output of the infrared detectors and provides a
means of compensating for minor differences in detector performance.
o. Auxiliary Control Module. The auxiliary control module provides an interface
between the aviator's control panel and the postamplifier module. The interface is
for such functions as level and gain adjustments and polarity selection or reversal.
p. Focus Drive Power Supply Module. The focus drive power supply module
incorporates an adjustable potentiometer, which varies an electrical signal sent to
the focus wedge assembly. The potentiometer is adjusted, as necessary, to focus
the PNVS properly for all objects from about 10 feet to infinity.
C-2. MODULAR FLIR
a. The FLIR system is built around a common set of modules with systempeculiar components. These components tailor the system to meet specific
performance objectives. The PNVS and the TADS on the AH-64 use, as a base,
separate but identical common-module components.
b. The common-module FLIR approach offers performance and configuration
control and provides significantly reduced cost through reliance on common
equipment. Figure C-3 shows the common-module block diagram. The common
modules are optical, mechanical, signal conversion, and electrical.
(1) Optical. Optical components include the infrared imager and visual
collimator.
(2) Mechanical. Mechanical components include the scanner and cooler.
(3) Signal conversion. These components include the detector-dewar and
LED array.
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(4) Electrical. These components include the preamplifier, postamplifier,
scan and interlace, bias regulator, auxiliary control, and inverter.
Figure C-3. Common-module block diagram
c. System-peculiar components are the shroud window, elevation mirror
assembly, focus wedge assembly, optical relay, and EO Mux.
C-3. COMPONENT OPERATION
a. The common-module and system-peculiar components collect, measure, and
ultimately convert infrared radiation from objects within the viewed scene into
video signals. The video signals are then projected on a video display device for
viewing by the aviator. Figure C-4 shows the FLIR turret assembly.
b. The basic flow described below shows how FLIR components produce an
image or a picture of the viewed scene.
(1) Step 1. Infrared energy radiated from the viewed scene passes through
an afocal assembly into the mechanical scanner module.
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Figure C-4. FLIR turret assembly
(2) Step 2. Infrared energy reflects off the front side of a two-sided mirror.
The energy passes through an infrared imager, which directs the energy
onto the infrared detectors in the detector-dewar module.
(3) Step 3. The detectors convert this energy to electrical signals. These
signals are then sent through the preamplifier to the postamplifier module.
(4) Step 4. The signal outputs of the postamplifier are applied to the LED
array, which converts the electrical signals into a visual image.
(5) Step 5. The visual image then passes through a visual collimator,
which directs it onto the back side of the mechanical scanner mirror.
(6) Step 6. The image then reflects off the mirror onto the face of the EO
Mux.
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(7) Step 7. The EO Mux outputs video signals, which are remoted to a
display device (TV) for viewing by the aviator.
C-4. BORESIGHTING
a. Once aviators have successfully completed IHADSS boresighting procedures,
they may adjust their seat heights as desired for flight. However, the IHU must
remain within the motion box. If necessary, aviators may disconnect and then
reconnect the IHU electrical connector. This action will not affect the stored
boresight bias.
b. The SEU stores the boresight bias until the aviator shuts off electrical power to
the IHADSS or again actuates the BRSIT/MODE switch while in the boresight
mode. Each aviator must boresight the IHU before operating it so that the SEU
will know what bias to apply during operational computations.
c. After the aviator completes the boresighting procedure, the HMS should be
capable of measuring the electrical LOS of the infrared detectors and the IHU.
Likewise, it should be capable of factoring-in the boresight bias and of providing
the PNVS with an accurate electronic duplication of the aviator's visual LOS. The
total LOS error should not exceed ±0.57 . If PNVS components are functioning
properly, the PNVS should point along the LOS determined by the aviator with a
total error of not more than ±1.07 . Rather than accept system accuracy on faith,
the aviator should perform a registration check.
C-5. FLIR SENSOR OPTIMIZATIONK
a. FLIR optimization is the combination of level and gain settings, which
produces the most detail in the displayed image. From these settings, an
adjustment of either control in either direction produces less detail and degrades
the image quality of the FLIR. The level and gain controls on the display control
panel are used to accomplish FLIR sensor adjustments. Both controls affect
postamplifier output voltages to the LED array.
NOTE: The aviator cannot optimize the FLIR sensor unless he has first optimized the
IHADSS display.
b. Proper adjustment of the FLIR provides the highest possible resolution picture
for the operating environment at the time of adjustment. If the PNVS is operating
properly, scene content (such as terrain and metal buildings), temperature,
humidity, atmospheric conditions, and range to the viewed objects will determine
the image quality of the FLIR.
(1) The level control establishes a voltage to the entire LED array that
lights the LEDs as desired by the aviator. The LEDs brighten or darken in
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response to electrical voltages from the infrared detectors, as controlled by
the gain control and polarity circuitry.
(2) The gain control increases or decreases the amplitude of the
postamplifier output to each LED. Thus infrared detector signals can drive
each LED at a brightness or an intensity that provides the highest possible
detail to the aviator.
c. The level control regulates the overall intensity or brightness of the total LED
array. An increase in the level control uniformly increases the intensity or
brightness of the total LED array. Conversely, a decrease in the level control
uniformly reduces the intensity of the total LED array. This is presented on the
HDU as a brightening or darkening of the total display. The aviator should
increase or decrease the level control as necessary to bring the significant object
signals (whether "hot" or "cold") within the dynamic range of the LED array.
d. The gain control also affects the intensity of the LED array but on an individual
LED basis. The gain control regulates the response of each LED to the electrical
signal produced by the infrared detectors. Each infrared detector in the detector
array is electronically connected through the preamplifiers and postamplifiers to
one LED within the LED array. An increase in the gain control results in an
increase in the amplitude of the electrical signal, leaving the postamplifier to
power an LED. Conversely, a decrease in gain control results in a decrease in the
amplitude of the electrical signal. If the gain control is increased, an LED will be
brightened or dimmed to a greater extent or degree than when the gain is
decreased. For example, an LED response to an infrared detector signal is
increased with an increase in gain and decreased with a decrease in gain. This is
presented on the HDU as a variation in intensity between the shades of grey
within the total display. Aviators will perceive a reduction in gain on the display
as a softening or clouding of the image. Increases in gain result in a reduction of
the apparent cloudiness in the image until only black and white are visible with no
shades of grey between them.
e. To accomplish initial FLIR adjustments (FLIR cool down complete and ACM
switch in MAN), the aviator-(1) Turns the level and gain controls fully counterclockwise. This will
completely darken the display.
(2) Advances the level control clockwise until the LEDs illuminate or
bloom. The display will begin to brighten.
(3) Continues to advance the level control just slightly beyond the point
that the LEDs illuminate and then stops the advance.
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(4) Advances the gain control clockwise until obvious variations in
shading appear in the display and then stops the advance.
NOTE: Specific definition of objects in the scene is not possible until the FLIR has had
several minutes to cool. FLIR optimization cannot occur until FLIR cool down is
complete.
f. Three conditions must be met before and during FLIR optimization. The aviator
must-(1) Select a scene which is potentially rich in detail or best represents the
planned flight environment.
(2) Select the desired polarity.
(3) Minimize head movement and, consequently, PNVS movement in
azimuth and in elevation while adjusting either the level or the gain
control.
NOTE: Only one control can be adjusted at a time. Both controls must never be moved
simultaneously.
g. To complete FLIR optimization (cool down complete and ACM switch in
MAN), the aviator-(1) Notes the position of the level control before adjusting it and indexes
that position by placing his thumb on top of the knob. He rotates the level
control first clockwise and then counterclockwise from the initial setting
while observing the effect on the FLIR image. Clockwise rotation tends to
brighten the display until it becomes too bright and eventually unusable.
Counterclockwise rotation tends to darken the display until it eventually
disappears.
(2) Continues to rotate the control clockwise as long as image detail
increases. When image improvement stops and degradation (too bright)
begins, the aviator stops the rotation. If the aviator observes immediate
image degradation when he rotates the level control clockwise, he stops
the rotation and returns to the initial setting.
(a) Image quality may improve when the aviator rotates the level
control clockwise. If this occurs and the control was adjusted to the
right of the initial setting (as indexed by the aviator's thumb), the
new level position is the optimum setting. The aviator will not
have to evaluate the counterclockwise direction because image
quality will not improve as he moves the level control in both
directions from the initial setting. If, however, image quality does
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not improve, the aviator must return the level control to the initial
setting. He must slowly turn the control counterclockwise. If image
detail increases, the aviator continues to rotate the control
counterclockwise until improvement stops and degradation (too
dark) begins. If the aviator observes an immediate image
degradation as he rotates the level control counterclockwise, he
stops the rotation and returns to the initial setting.
(b) The aviator may observe an improvement in image quality as
he rotates the control counterclockwise. If this occurs and the
control was adjusted to the left of the initial setting, the new level
position is the optimum setting. If the aviator observes an
immediate degradation and the level control was returned to the
initial setting, the initial setting is the optimum setting.
(3) Notes the position of the gain control after completing level control
adjustments. He indexes that position by placing his thumb on top of the
gain control knob. The aviator rotates the gain control first clockwise and
then counterclockwise from the initial setting while observing the effect
on the FLIR image.
(a) The aviator will observe an intensification of the dark and light
shades in the FLIR image when he rotates the gain control
clockwise. With continual clockwise rotation, the aviator will
observe only extremely light or dark shades; subtle shading
variations with corresponding detail are lost.
(b) The aviator will observe a decrease in the intensity of the dark
and light shades in the FLIR when he rotates the gain control
counterclockwise. Continual counterclockwise rotation will result
in all, or nearly all, detail being washed out of the image.
(c) The aviator evaluates gain control positions to the right and left
of the initial setting by following the procedures described in (1)
and (2) above for level control adjustment.
(4) Ensures FLIR optimization has been achieved after adjustment of both
level and gain controls. He does this by returning to the level control and
briefly reconfirming that it has been optimized. If level optimization
requires a change in position, the aviator reconfirms that the gain control
is still optimized.
h. FLIR optimization described above is appropriate only for the scene viewed
and the existing atmospheric conditions at the time of the optimization. In PNVS
flight training, the aviator initially performs FLIR optimization at a prepared
airfield facility. This means that he uses primarily man-made objects to adjust the
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FLIR. The strong thermal signatures available in such a scene normally produce a
high-quality FLIR image and make FLIR optimization a relatively simple task.
Flight at altitude, away from the prepared facility toward the training area, may
also produce a relatively high-quality image. However, arrival at the training site,
with its comparative absence of man-made objects, will emphasize the importance
of proper optimization procedures. Generally, changes in the atmospheric
environment and scene content will only require minor adjustments of the level
and gain controls after the FLIR is initially optimized. However, minor
adjustments can produce major changes in scene clarity and can enhance or
inhibit an aviator's ability to operate in the terrain flight environment. To ensure
the effectiveness of the FLIR, aviators must employ optimization techniques in a
timely manner when FLIR image degrades to a point where it lacks detail or is of
poor quality.
i. Aviators must clearly understand and effectively practice the principles of FLIR
optimization. These principles are stated below.
(1) Minor adjustments of the FLIR level control, gain control, or both may
be required as the atmospheric environment or scene content changes
during the flight period.
(2) Aviators must accomplish all FLIR adjustments using only one control
at a time to optimize the FLIR image.
(3) The FLIR is optimally adjusted when any movement (left or right) of
the level and gain controls from their optimized positions will result in
image degradation. This condition defines the best FLIR obtainable for
any given operating environment. However, the FLIR image quality may
still be less than desired or, in extreme cases, even unsuitable for flight.
(4) FLIR imagery is provided in either of two selectable polarities. When
optimization is less than desired in the preferred polarity, the aviator
should select the other and optimize again.
C-6. INFINITY FOCUS CHECK
a. Infinity focus is a condition of focus at the HDU where the FLIR image and
flight symbology are perceived as in clear focus. A clear focus is achieved while
the human eye viewing the HDU focuses on an object at least 200 feet away.
b. The human eye is more relaxed while focused at infinity. For that reason, the
PNVS FLIR is designed, electrically and mechanically, to provide imagery to the
HDU at an infinite focus.
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c. The variation in visual acuity among aviators is compensated for by a focus
ring on the HDU. The focus ring allows each individual to focus the image to
infinity.
NOTE: If symbol brightness is advanced to full bright, the symbols will appear blurred
and possibly be misinterpreted as an out-of-focus condition.
d. If the aviator judges the HDU to be out of focus, he should adjust the manual
focus ring on the aft portion of the HDU. If he focuses the HDU and, therefore,
his eye at anything less than infinity, muscular tension will result and eyestrain
will occur within a short time. This will cause eye pain, a headache, or both. If
this condition is not corrected, degradation in aviator performance may occur.
C-7. SIZING AND CENTERING PROCESS
a. With the sizing and centering adjusted correctly, a 30 by 40 FOV with unity
magnification is presented to the aviator. To accomplish sizing and centering, the
aviator-(1) Adjusts brightness and contrast to full on (clockwise). This allows him
to see the mask on the field flattener lens by lighting the grey scale
background. The field flattener lens on the face of the CRT has a mask
(dark border). It is used as a reference during the sizing and centering
process.
(2) Observes the white outer border of the grey scale. If the border is
adjacent to the mask on the field flattener lens on all sides, no adjustment
is required. The aviator must move his eyes left and right to see the mask
and border.
(3) Ensures proper focus of the FOV before continuing the sizing and
centering adjustment. The aviator must adjust the mechanical focus ring
on the HDU and, if necessary, the electronic focus potentiometer on the
DAP for the best focus. When the FOV is properly focused, the aviator
can clearly distinguish raster lines while viewing the display.
(4) Correctly positions the combiner assembly.
(5) Adjusts horizontal sizing and centering potentiometers as necessary to
make the grey scale border, top and bottom, adjacent to the mask.
(6) Adjusts the vertical sizing and centering potentiometers as necessary to
make the grey scale border, top and bottom, adjacent to the mask.
NOTE: An IHADSS boresight is required after any sizing and centering adjustment.
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b. After the aviator completes the sizing and centering adjustments, all symbology
should be visible. Any loss of symbology is a result of improper helmet fit,
display position, combiner extension, or the wearing of eyeglasses.
C-8. UNITY MAGNIFICATION CHECK
a. Unity magnification is a one-to-one size relationship between objects observed
on the HDU and their real-world counterparts. The size of a tree or building
viewed on the HDU is judged to be identical to the size of the actual object
viewed directly without the HDU.
b. An aviator under VMC perceives distances to objects and closure rates through
three-dimensional, wide FOV, binocular vision. An aviator flying with the PNVS
views the world through a narrow FOV FLIR and a two-dimensional monocular
display. The absence of the third dimension, which provides depth perception, and
the restricted FOV of the sensor, necessitate a new method for perceiving
distances and closure rates.
c. The adverse effects of a narrow FOV sensor are compensated for through turret
slewing. This provides the aviator with a total field of regard much larger than the
FOV. The loss of depth perception is compensated for through the observation of
size and the relative changes in the size of objects visible on the display. In this
manner, the aviator obtains a panoramic view of the terrain by turning his head.
He judges distances and closure rates by the size and relative changes in the size
of objects visible within his viewing area.
d. Because an aviator flying with the PNVS must rely on perceived object size on
the display for depth perception information, he must operate the PNVS at unity
magnification. Objects visible in the thermal scene viewed by the aviator must
appear to be the same size as when he views them unaided from the same
perspective point as the FLIR sensor. Unity magnification exists only when the
aviator's HDU projects thermal imagery to the aviator's eye in a 30 by 40 format.
This format matches the FOV of the FLIR sensor and provides a one-to-one
relationship between the display FOV and the sensor FOV.
e. The one-to-one relationship between the aviator's view of the thermal image
and the FLIR's view of the real world is affected by DAP adjustments. Normally,
maintenance personnel are responsible for adjusting the DAP. These adjustments
usually are required only when the HDU or DAP is replaced. The aviator can
ensure a 30 by 40 format is present on the HDU by selecting the grey scale and
noting the position at the boundary lines surrounding the grey scale bars. When
properly adjusted, these lines are at the limits of the display. Additionally, the
corners of the display are obscured as a result of the 40 FOV limitation of the
0.75-inch CRT within the HDU.
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f. The technique of superimposing objects in the thermal imagery over closeproximity, real-world objects to check for unity magnification can be misleading.
This is because of the difference in physical perspective points between the FLIR
sensor and the FLIR display. The aviator may, however, minimize the effect of
parallax by orienting his view straight forward and overlaying prominent objects
on the horizon to ensure unity magnification. This procedure may be
accomplished in either the fixed forward mode or with the turret slaved to the
aviator's IHU.
g. Magnification of the FLIR imagery results when the aviator's display format is
greater than 30 by 40 . This condition causes objects in the thermal scene to
appear larger than their real-world size. This may cause an aviator to miscalculate
the distance of the objects based on their size and perceive them to be closer than
they actually are. Conversely, display minification results when the display format
is less than 30 by 40 . This condition causes objects in the thermal scene to appear
smaller on the display than their real-world size. Again, an aviator may
miscalculate the distance of the objects based on their size and perceive them to
be farther away than they actually are.
C-9. REGISTRATION CHECK
a. Registration is performed to ensure that the PNVS turret is, in fact, looking at
the same point as that of the aviator's eye. When the aviator boresights the PNVS,
he electrically corrects for minor errors between his visual LOS and the electrical
LOS of the IHU. A good helmet fit is important not only for aviator comfort but
also for maintaining proper boresight. If, after boresighting, the aviator shifts his
helmet for any reason, he will have changed the relationship between his visual
LOS and the IHU's electrical LOS. This change in LOS relationship can result in
a perceivable difference between where the aviator is looking and where the
PNVS turret is pointing.
b. The registration check is designed to confirm that the aided eye LOS and the
PNVS turret LOS are aligned. To perform proper registration, the aviator-(1) Aligns the aircraft with an object along the 0 AZ and 0 EL line
(represented by the head tracker symbol). The object being used must be
at least 90 feet in front of the PNVS turret. If the object is not aligned
along the 0 AZ and 0 EL (aircraft LOS) line or is closer than 50 feet,
accurate registration will not be possible because of parallax.
(2) Views the real-world object with his aided eye through the combiner
lens by centering the PNVS LOS over the object. This is accomplished
after the aviator properly aligns the aircraft and the selected object. If the
real-world, through-the-lens view of the object and the FLIR image of the
same object are superimposed, the PNVS is properly registered.
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(3) Uses a slightly different technique for night registration. At night the
registration point is an individual stationed at the front of the aircraft
within the head tracker symbol. This individual holds a flashlight visible
to the aviator. The light is held in the center of the torso. This allows the
aviator to determine the real world and image alignment. By viewing the
flashlight, the aviator is able to determine the registration point in a
darkened environment.
NOTE: Specifications allow for an approximate displacement of the image and object. A
1-foot displacement for a 90-foot distance is permitted.
c. If the real-world image and the FLIR image are not superimposed within the
specification limit during the registration check, the aviator must perform the
registration alignment procedure.
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APPENDIX D
TRAINING PROGRAMS
The conduct of proper training is the peacetime leader's most difficult but most important
job. In recent years, a number of factors have made unit training more difficult and
complex. These factors include decreased training time, doctrinal changes, complex
equipment, time-consuming maintenance requirements, personnel turnover, and
insufficient training areas.
D-1. ESTABLISHMENT CRITERIA
The aviation unit commander must decide what type of night training program will best
support his unit's mission. This training program may require night training with and
without aircraft lighting and training with night vision devices. The training program
developed by the commander must be based on the appropriate ATM. However, a
successful program depends on adequate support such as flight hours, equipment, training
areas, and personnel. Before the commander initiates an unaided or aided night training
program, he must ensure it can be supported and continued.
D-2. LIGHTS-OUT NIGHT VISION DEVICE TRAINING
In March 1984, the FAA issued a grant of exemption to FAR Sections 91.73(a) and (b) so
that the US Army could conduct a part of its aided night training with aircraft position
lights out. The exemption permits commanders, at their discretion, to authorize aided
night training in a lights-out mode subject to certain conditions and limitations, as shown
in Figure D-1. For additional information or clarification, personnel should contact Army
Aeronautical Services, Cameron Station, Alexandria, VA 22304-5050, AUTOVON 2847796/6304, commercial (202) 274-7796/6304, or FTS 274-7796/6304.
1. This exemption is limited to night vision flight training in U.S. Army tactical
helicopters.
2. Safety Observers.
a. An airborne training operation-(1) may be conducted in a flight of two or more helicopters with a
dedicated observer on duty aboard each helicopter. The flight shall
be conducted in such a manner as to enable the observers
collectively to survey fully about the entire flight for
nonparticipating aircraft; or
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Figure D-1. Extract of FAA grant of exemption to FAR Sections 91.73(a) and (b)
(2) shall be escorted by a properly lighted aircraft serving as an
observation platform dedicated to surveillance for nonparticipating
aircraft.
b. Traffic notifications from the observer to the training flight shall be
timely commensurate with the position and speed of the observed
nonparticipating traffic.
c. When nonparticipating traffic is relevant, the pilot of each training flight
aircraft shall light that aircraft's position lights and keep them lighted until
the traffic is no longer relevant.
3. Airborne operations may not be conducted above 200 feet above the surface
and must be contained within a prescribed and publicized area that-a. is simply defined, e.g. the radius area of a point or location;
b. is established in an area of low traffic density;
c. is not within 5 miles of any public use airport;
d. does not infringe upon FAA-designated airspace areas, e.g. control
zones and airport traffic areas; and
e. has been coordinated with the appropriate FAA Region's Air Traffic
Division and Flight Standards Division Offices.
4. Notwithstanding paragraph 3 above, each operation must be conducted in
accordance with Section 91.79, Minimum safe altitudes;--general.
5. The holder shall advertise each approved training area to operators at all
airports within 50 miles of the area for 60 days preceding its initial use.
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6. Ground (airport/staging area) operations in noncompliance with FAR Section
91.73(b) may be conducted at locations where only the holder's aircraft involved
in night vision flight training are operating and suitable alternative measures for
collision avoidance are instituted.
7. The holder shall establish procedures for collision avoidance among its aircraft
operating pursuant to this exemption, including observer aircraft.
8. Each pilot who will conduct operations under this exemption must be
thoroughly familiar with its provisions.
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Figure D-1. Extract of FAA grant of exemption to FAR Sections 91.73(a) and (b)
(continued)
D-3. SUPPORT REQUIREMENTS
The success of a night training program depends on the support provided before, during,
and after the flight. If the required support is not provided, an unsafe training
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environment can result. Support requirements for night flight training are discussed
below.
a. Flight Routes. Numerous flight routes should be established. Consideration
must be given to avoiding obstructions and built-up areas. While a day NOE route
may be acceptable for use at night, aircrews should check it at night for excessive
lights. Likewise, before aircrews fly a route at night, they should fly it during the
day to check for obstructions not present during the last flight. A hazard map must
be posted in the briefing room and updated when a new obstruction is identified.
b. Lighting. The commander should ensure the airfield lighting system is
configured for night training. If the primary field is not adaptable for night
training, a field landing site or stagefield can be used. Tactical lights for both
unaided and aided flight are required at a field landing site.
c. Flight-Following. A command and control or cover aircraft should be used
during qualification training. Otherwise, flight-following procedures should be
established and maintained. If a command and control or cover aircraft is used,
that aircrew must be familiar with the routes being flown and have night vision
devices available. Responsibilities of the aircrew flying command and control or
cover include-•
•
•
•
Performing flight-following functions.
Ensuring aircraft separation during training.
Directing crash-rescue personnel in case of a downed aircraft.
Terminating training when communication, safety, and weather criteria are not
met.
D-4. TRAINING EQUIPMENT
A major training goal of aviation unit commanders is to conduct realistic night training.
To accomplish this goal, units must perform realistic training during low ambient light
conditions. Realistic night training is more costly than day training. This is because of the
limitations imposed by moon-phasing angles, percent illumination, crew endurance, and
aircraft availability. Some of the systems developed to help overcome these limitations
are discussed below.
a. Daylight Filter. A variable density filter to simulate night flight during the day
is available for the AN/PVS-5A with full faceplate. However, use of the filter
does not duplicate what aircrews actually experience when they view lights at
night.
b. SFTS. An SFTS compatible with I2 devices can be used effectively to teach a
wide range of flight tasks with these devices. When I2 devices are used in the
UH1FS, windows should be covered to reduce the amount of light entering the
cockpit.
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c. Pink Light Filter or Infrared Band-Pass Filter. The pink light filter or infrared
band-pass filter is required during certain low illumination levels.
D-5. TRAINING PREREQUISITES
a. Academic Training. Students should receive academic instruction before they
undergo night flight training. Academic training will make students aware of the
limitations of night terrain flight and thus help ensure a safer operating
environment.
b. Flight Training. Students must complete a day terrain flight course of
instruction before they conduct night terrain flight. The techniques of day terrain
flight closely parallel those of night terrain flight and serve as a basis for
expanding a student's knowledge of terrain flight. Students without previous
terrain flight training pose a high safety risk during night terrain flight. Flight
training should be conducted according to the appropriate ATM. Night terrain
flight training must be conducted in the type of helicopter the aviator will fly
during tactical missions.
D-6. FACILITY REQUIREMENTS
Appropriate flight facilities are essential for the conduct of night training. When unaided
and aided aircrews are using the same training area, aided aircrews will operate at 200
feet and below and unaided aircrews at 300 feet and above. Corridors must be designed
so that unaided and aided aircrews do not operate in the same corridors at the same
altitudes. For night training, commanders should ensure-•
•
•
•
•
•
•
•
•
Red lights are installed in briefing rooms.
Ground personnel are provided compatible lights.
Ground personnel are provided I2 devices if required.
Nonessential lights on the flight line are extinguished.
Takeoff and approach routes are away from illuminated areas.
Unlighted and lighted aircraft do not operate in the same traffic pattern.
Headlights on maintenance vehicles and fuel trucks are masked or filtered.
Aircraft for night training are parked as far away from lighted areas as possible.
Adequate hover lanes are provided so that aviators can hover aircraft without the
use of landing lights.
D-7. UNAIDED AND AIDED NIGHT FLIGHT TRAINING
Night operations enhance survivability and provide a 24-hour combat capability. These
operations are possible only when aircrews are fully trained and able to employ aircraft in
the unaided and aided night modes of flight.
a. Training Guide. Each ATM provides a guide for training individual aviators.
TC 1-210 provides a guide for--
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•
•
•
•
Predicting and allocating unit flying hours.
Computing unit training status based on individual aviator proficiency.
Developing aviator qualification, refresher, mission, and continuation training
programs.
Evaluating the status of individual aviators so that training can be tailored to the
individual's needs.
b. Responsibilities.
(1) Commanders. Aviation unit commanders manage the ATP according
to AR 95-1 and TC 1-210.
(2) Unit evaluators. Unit evaluators include instrument flight examiners,
standardization instructor pilots, and instructor pilots. Unit evaluators
assist and advise the commander in administering the ATP.
(3) Unit trainers. Unit trainers assist the commander and unit evaluators in
administering the ATP.
(4) Aircrews. All aircrews must conscientiously support the ATP and
accomplish the training tasks developed by the commander.
c. Training Procedures. Training should begin with simple tasks and progress to
more difficult tasks.
(1) Individual training should begin in high ambient light levels, such as
the full moon, and progress to lower and lower light levels.
(2) Aviators should first perform maneuvers to prepared surfaces. As
proficiency increases, aviators can progress to lighted field sites and then
to unlighted field sites.
(3) Navigation training should begin with easy routes. As aviators become
proficient, they can fly routes with legs of 50 to 100 nautical miles. More
difficult and realistic scenarios have landing areas and FARPs interspersed
along the route.
(4) Individuals, instructor pilots, and unit trainers should be trained first,
followed by crews.
(5) Aircrews should be trained first in single-ship operations. Training in
multihelicopter operations should begin with two aircraft. As training
progresses, larger formations can be used.
d. Night/Night Vision Goggle Training Extension Course 5800 Series. This
course provides units and institutions with exportable, performance- oriented
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training packages. The lessons are self-paced and assist the crew member in
acquiring and maintaining critical night and NVG skills. Each lesson can be used
by individuals or small groups. The lessons support and supplement unit IP
instruction. The course is issued as Night Flight Training, BOI 166. Units can
establish an account by contacting Commander, US Army Training Support
Center, ATTN: ATIC-ETS-DS, Fort Eustis, VA 23604-5168.
e. Night Vision Goggle Exportable Training Package. Units can order this
package by writing to the Directorate of Aviation Proponency, Training Support
Division, ATTN: ATZQ-DAP-TS, Fort Rucker, AL 36362-5039.
D-8. STANDING OPERATING PROCEDURES
Many different and demanding requirements are placed on aircrews and units during
unaided and aided night flight training. This necessitates a thorough SOP. The SOP
should cover all aspects of the training program; guidance in it should be specific. Each
unit must develop an SOP that meets its specific training needs. All crew members must
become thoroughly familiar with the contents of the SOP.
a. Unaided and Aided Night Training SOP. The information in this SOP should
cover all aspects of unaided and aided night flight training and unit operations. As
a minimum, the SOP should include-•
•
•
•
•
•
•
•
•
•
•
•
•
•
Crew duties.
Standardized terminology.
Disorientation procedures.
Standardized radio configuration.
Care and security of night vision devices.
Unaided and aided flight routes and requirements.
Vertical helicopter instrument recovery procedures.
Weather requirements for unaided and aided night training.
Additional light sources authorized for aided night flight.
Illumination requirements for unaided and aided night flight.
Special tactical operations such as multihelicopter operations and FARP
operations.
Command and control or cover aircraft requirements for unaided and aided night
operations.
Crew endurance requirements for unaided and aided night flight, to include
allowable flight time.
Aircraft lighting configurations and modification requirements for unaided and
aided night flight.
b. Unaided and Aided Night Operations Area and Stagefield SOP. Information in
this SOP should be specifically concerned with training area utilization. Figure D2 shows a sample outline of a unit SOP for unaided and aided night operations
areas and stagefields.
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1. GENERAL. The procedures in this SOP will be followed by all personnel
during unaided or aided night training to ensure safe operations. All aviators
entering traffic must have been briefed on training site procedures. Otherwise,
they will land and receive a briefing from the officer in charge or tower
noncommissioned officer in charge. All personnel will be familiar with this SOP,
AR 95-1, and the appropriate ATM.
2. TRAINING REQUIREMENTS.
a. Location.
b. Field elevation.
c. Runway heading.
Figure D-2. Sample outline of SOP for unaided and aided night operations areas
and stagefields
d. Frequencies.
e. Weather minimums.
(1) Ceiling and visibility.
(2) Wind.
f. Safety considerations.
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(1) Familiarization with training site during daylight hours before
night flight.
(2) Establishment of maximum density for aircraft in the training
site.
3. SPECIAL INSTRUCTIONS.
a. Aircraft lighting.
b. Airfield lighting for training.
c. Safety standards for the training area personnel.
d. Safety standards for the training area vehicles.
e. Traffic patterns.
(1) Entry and exit procedures.
(2) Call signs.
(3) Pilot procedures.
(4) NVG failure procedures.
f. Parking and refueling.
g. Aircraft mishap procedures.
h. Emergency procedures and signals.
D-10
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Figure D-2. Sample outline of SOP for unaided and aided night operations
areas and stagefields (continued)
D-11
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GLOSSARY
ACRONYMS AND ABBREVIATIONS
A2C2 - Army airspace command and control
AC - alternating current
ACA - airspace control authority
ACM - automatic contrast
ACP - air control point
ADA - air defense artillery
AGL - above ground level
AH - attack helicopter
AHO - above the highest obstacle
AL - Alabama
AM - amplitude modulation
AMC - air mission commander
ANVIS - aviator's night vision imaging system
AO - area of operations
AR - Army regulation
arm - armament
ATC - air traffic control
ATM - aircrew training manual
ATP - aircrew training program
attn - attention
AUTOVON - automated voice network
Glossary-1
TC 1-204
AZ - azimuth
B - blue
BMNT - beginning of morning nautical twilight
BRSIT - boresight
BRU - boresight reticle unit
CG - center of gravity
CHUM - Chart Updating Manual
CL - centerline
C-NITE - Cobra NITE sight
CPG - copilot-gunner
CRT - cathode ray tube
DA - Department of the Army
DAP - display adjust panel
DC - direct current
DEATH - drugs, exhaustion, alcohol, tobacco, and hypoglycemia
dist - distance
EENT - end of evening nautical twilight
e.g. - for example
EHF - extremely high frequency
EL - elevation
EO Mux - electro-optical multiplexer
ETL - effective translational lift
F - Fahrenheit
Glossary-2
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FAA - Federal Aviation Administration
FAR - Federal Aviation Regulations
FARP - forward arming and refueling point
FLIR - forward-looking infrared radar
FM - field manual or frequency modulated
FOV - field of view
FPM - feet per minute
FTS - Federal Telecommunications System
G - green
HA - holding area
hdg - heading
HDU - helmet display unit
HF - high frequency
HMS - helmet mounted sight
hq - headquarters
I2 - image intensifier
ICAO - International Civil Aviation Organization
ICS - internal communication/control system
IFR - instrument flight rules
IHADSS - integrated helmet and display sight subsystem
IHU - integrated helmet unit
IMC - instrument meteorological conditions
IP - instructor pilot
Glossary-3
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IR - infrared
JOG - Joint Operations Graphic-Air (map)
k - kelvin
KIAS - knots indicated airspeed
kt - knots
ldg - landing
LED - light emitting diode
LF - low frequency
LOS - line of sight
LZ - landing zone
m - meter
MAN - manual
METT-T - mission, enemy, terrain, troops, and time available
MF - medium frequency
MFP - modified faceplate
min - minute(s)
MMS - mast-mounted sight
mod - model
MRT - minimum resolvable temperature
MSL - mean sea level
NATO - North Atlantic Treaty Organization
NDB - nondirectional radio beacon
NM - nautical mile(s)
Glossary-4
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no - number
NOE - nap-of-the-earth
NOTAM - notices to airmen
NSN - national stock number
NVG - night vision goggles
OG - olive green
OPLAN - operation plan
OPORD - operation order
OPSEC - operations security
OR - orange
PC - pilot in command
PNVS - pilot night vision sensor
POL - petroleum, oils and lubricants
PZ - pickup zone
R - red
rmk - remarks
RPM - revolutions per minute
sec - second(s)
SEU - sight electronics unit
SFTS - synthetic flight training systems
SHF - super high frequency
SOP - standing operating procedure
STANAG - Standardization Agreement
Glossary-5
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std - standard
SW - shortwave
TADS - target acquisition and designation sight
TC - training circular
TM - technical manual
T/O - takeoff
TOW - tube-launched, optically-tracked, wire-guided missile
TRADOC - United States Army Training and Doctrine Command
TV - television
UH - utility helicopter
UHF - ultrahigh frequency
UH1FS - UH-1 flight simulator
US - United States (of America)
USAREUR - United States Army, Europe
UV - ultraviolet
V - violet
VA - Virginia
VAPI - visual approach path indicator
VASI - visual approach slope indicator
VFR - visual flight rules
VHF - very high frequency
VHIRP - vertical helicopter IFR recovery procedure
VLF - very low frequency
Glossary-6
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VMC - visual meteorological conditions
VOR - VHF omnidirectional range
x - unknown quantity
Y - yellow
Glossary-7
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REFERENCES
REQUIRED PUBLICATIONS
Required publications are sources that users must read to understand or to comply with
this publication.
ARMY REGULATION
AR 95-1 Army Aviation: General Provisions and Flight Regulations
AR 95-2 Air Traffic Control, Airspace, Airfields, Flight Activities and Navigation Aids
FIELD MANUALS
FM 1-202 Environmental Flight
FM 1-230 Meteorology for Army Aviators
FM 1-301 Aeromedical Training for Flight Personnel
TECHNICAL MANUALS
TM 9-1370-201-12 Operator's and Organizational Maintenance Manual (Including
Repair Parts and Special Tools List): Flare, Aircraft: Parachute, White, MK 45 MOD O
L473; Flare, Aircraft: Parachute, MK 45 MOD O With Adapter for Dispenser XM19
L424 and Dispenser, Flare: XM19 L106
TM 11-5855-238-10 Operator's Manual for Night Vision Goggles, AN/PVS-5 and
AN/PVS-5A AN/PVS-5B AN/PVS-5C
TRAINING CIRCULARS
TC 1-201 Tactical Flight Procedures
TC 1-210 Aircrew Training Program Commander's Guide
DA FORM
DA FORM 2028 Recommended Changes to Publications and Blank Forms
References-1
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Section II
RELATED PUBLICATIONS
Related publications are sources of additional information. They are not required in order
to understand this publication.
FIELD MANUALS
FM 1-140 Helicopter Gunnery
FM 17-95 Cavalry Operations
FM 100-103 Army Airspace Command and Control in a Combat Zone
TECHNICAL MANUALS
TM 11-5855-238-20 Organizational Maintenance Manual: Night Vision Goggles,
AN/PVS-5 and AN/PVS-5A
TM 11-5855-263-10 Operator's Manual for Aviator's Night Vision Imaging System,
AN/AVS-6(V)1 and AN/AVS-6(V)2
TM 55-1520-238-10 Operator's Manual for Army Model AH-64A Helicopter
References-2
TC 1-204
27 DECEMBER 1988
By Order of the Secretary of the Army:
CARL E. VUONO
General, United States Army
Chief of Staff
Official:
WILLIAM J. MEEHAN II
Brigadier General, United States Army
The Adjutant General
DISTRIBUTION:
Active Army, USAR, ARNG: To be distributed in accordance with DA Form 12-11E,
requirements for Night Flight Techniques and Procedures (Qty rqr block no. 721).
¶U.S. GOVERNMENT PRINTING OFFICE:1998-432-785/80524
PIN: 065107-000