windshear, microbursts, thunderstorms and

Transcription

ASSIGNMENT
COVER SHEET
GRIFFITH AVIATION
Course Code
2507NSC
Course Name
All Weather Aircraft Operations
Assessment Item Number
WRITTEN ASSIGNMENT (REPORT) 1
ASSESSMENT TITLE
WINDSHEAR, MICROBURSTS,
THUNDERSTORMS AND
LIGHTNING STRIKES:
PHENOMENA IDENTIFICATION
AND IMPACTS IN FLIGHT
DUE DATE
01-MAY-2015
Student Names and ID Numbers
REBECCA SPENCER
S2942503
MITCHELL TYNAN
S2941977
Course Convenor
Paul Lee
Word Count
3,223
0.0 EXECUTIVE SUMMARY
Flying into unexpected weather conditions has resulted in numerous aviation incidents and
accidents. This report intends to research into four weather phenomena which contribute to
adverse flight. Each section begins with a description of the weather phenomenon,
highlighting its impacts to flight operations through the study of previous weather induced
accidents. Identification of these conditions via visual cues and forecasting is then discussed.
Windshear was found to be particularly hazardous for operations near airports, where lowlevel wind changes can lead to aircraft overshooting runways or touching down harder than
expected. Though difficult to detect, pilots should continuously check for windshear
observations before commencing a take-off or landing.
Microbursts have similar effects on aircraft performance, as windshear occurs throughout this
phenomenon. With headwinds changing into tailwinds, an aircraft will have reduced lift,
seeing to an increased rate of descent if landing. Microbursts can be detected by visual
means, particularly by cloud observations.
Thunderstorms are associated with heavy rain, hail, strong wind gusts and lightning strikes.
Based on the strength of downwinds and upwinds, a thunderstorm can be divided into the two
main categories of a normal cell and super cell. They can be formed through convection,
orographic lifting and widespread ascent - such as cold fronts associated with cumulus cloud
development.
Lightning strikes are associated with thunderstorms and can result in structural damage of an
aircraft and internal damage from surges. Pilots can forecast for these events using visual
cues for identifying thunderstorms, forecast charts such as ARFOR, TTF, TAF from Air
Services Australia or Bureau of Meteorology sites, the latter resource also provide radar
maps.
GU |2507NSC | NSC | Assignment 1 (Report)| Spencer (s2942503) & Tynan (s2941977) | Page 1 of 38
Table of Contents
0.0
EXECUTIVE SUMMARY ............................................................................................................. 1
0.1 Glossary ......................................................................................................................................... 4
0.2 List of Figures ................................................................................................................................ 5
1.0
INTRODUCTION ....................................................................................................................... 6
2.0
WINDSHEAR ............................................................................................................................ 7
2.1 Affects for Aircraft Airspeed and Vertical Speed ...................................................................... 7
2.1.1 EXAMPLE: Increased Tailwind with VH-NQE .......................................................................... 8
2.1.2 EXAMPLE: VH-VQT Evening Flight with Thunderstorm Conditions ........................................ 8
2.3 Forecasting Windshear ............................................................................................................. 9
3.0
MICROBURSTS ...................................................................................................................... 10
3.1 Formation ................................................................................................................................ 10
3.2 Effect on Aircraft Performance ............................................................................................... 11
3.2.1 EXAMPLE: Downdraft Affects In Flight VH-ZIC ..................................................................... 12
3.3 Wet and Dry Microbursts ........................................................................................................ 12
3.3.1 EXAMPLE: Wet Microburst During Flight VH-VQT ............................................................... 13
3.5 Visual Identification of Microbursts ........................................................................................ 13
4.0
THUNDERSTORMS................................................................................................................ 15
4.1 Formation of a Thunderstorm ................................................................................................ 16
4.2 Lightning Formation ................................................................................................................ 17
4.3 Effects of Lightning Strikes on Aircraft .................................................................................... 17
4.3.1 EXAMPLE: VH-LBC Lightning Strike Accident ....................................................................... 18
4.4 Identifying and Forecasting for Thunderstorms ..................................................................... 18
4.4.1 ARFOR .................................................................................................................................. 18
4.4.2 TAF ....................................................................................................................................... 19
4.4.3 TTF ........................................................................................................................................ 20
5.0
CONCLUSION ....................................................................................................................... 21
6.0
REFERENCE LIST: .................................................................................................................. 22
Appendix 1 – Summary for Flight with Windshear Incident ............................................................. 26
Appendix 2 – Summary of Windshear Encounter During Flight ....................................................... 27
Appendix 3 – Summary of Microburst Flight Incident ...................................................................... 28
Appendix 4 – Summary of Lightning Strike Accident ........................................................................ 29
Appendix 5 – Recorded Events Relating to Airspeed and Descent Rate for VH-NQE ....................... 30
Appendix 6 – Sectors of Australia for Which ARFORs are Issued ..................................................... 31
Appendix 7 – ARFOR Example (Using Area 20: Sydney Region) ....................................................... 32
Appendix 8 – Time Conversions for UTC (Zulu) Time ....................................................................... 33
Appendix 9 – Abbreviated Codes Used for ARFOR Weather Descriptions ....................................... 34
Appendix 10 – TAF for Sydney and Coffs Harbour Areas .................................................................. 35
Appendix 11 – TTF for Sydney Area .................................................................................................. 36
Appendix 12 – BoM Radar Loop for Sydney Area ............................................................................. 37
Appendix 13 – BoM Radar Loop for Williamtown ............................................................................ 38
0.1 Glossary
A320-232
Airbus aircraft
AGL
Above Ground Level
ARFOR
Area Forecast
AMSL
Above Mean Sea Level
ATC
Air Traffic Control
ATSB
Australian Transport Safety Bureau
BoM
Bureau of Meteorology
DALR
Dry Adiabatic Lapse Rate
F100
Fokker Aircraft
FPM
Feet Per Minute
kt
knot
nm
nautical miles
SALR
Saturated Adiabatic Lapse Rate
TAF
Aerodrome Forecast
TTF
Trend Forecast
0.2 List of Figures
0
– Microburst Genesis
1
– Flight Operation Through A Microburst
2
–Characteristics of Dry and Wet Microbursts
3
–Precipitation Curl of a Microburst
4
–Shelf Cloud
5
–Virga
6
–Supercell Storm Structure
7
–Formation of a Thunderstorm
8
–List of Abbreviations Used for Descriptions in an ARFOR
9
–Abbreviated Codes for Cloud Types
10 –Codes of Overall Cloud Coverage
11 –Codes for Cloud Amount
1.0 INTRODUCTION
For a pilot, flying through adverse weather conditions can be a daunting situation because of
the lack of aircraft control that can accompany it. What follows can lead to structural damage
of an aircraft and even fatalities. This report outlines four weather phenomena which can
potentially be hazardous to flight. For each phenomena, reported incidents and accidents have
been referred to, highlighting how weather can impact aircraft operations. Each section ends
with a detailed description of how a pilot should forecast for these events. All case studies
referred to throughout the report have a full summary in the appendices section.
2.0 WINDSHEAR
Windshear events result in sudden wind changes, in terms of wind velocity and direction,
which occurs over a relatively small area (Aviation Theory Centre, 2012), resulting in rapid
and intense wind flows. This adverse wind phenomenon can be found in any atmospheric
layer and is associated with thunderstorms and microbursts (Fujita, 1980).
The downdrafts of windshear are coupled with significant wind directional changes, which
can reduce aircraft controllability. Rapid changes from head to tail winds cause an aircraft to
accelerate “so that the resulting windshear inertia force can be as large as the drag of the
aircraft” (Burlisch, Montrone & Pesch, 1991, p 2). Burlisch et. Al. (1991) further note that
this resultant force can develop to a magnitude equal to the aircraft’s engine thrust (p2). This
large, potential force emphasises the great hazard associated between windshear and aviation.
Windshear is a potential hazard to flight operations as it affects both the flight path and
airspeed of an aircraft. The majority of windshear induced aviation incidents occur within
close proximity of airports, as the hazardous wind is particularly dangerous at the low-level.
Entering windshear with little altitude remaining, such as when taking-off or landing, does
not always leave enough scope for an aircraft to recover (Leitmann & Pandey, 1991). It also
leaves an insufficient amount of time for windshear warning systems to be sounded.
2.1 Affects for Aircraft Airspeed and Vertical Speed
Directional wind changes alter the amount of lift produced (BoM, 2014). For instance, if an
aircraft’s vertical component of headwind is reduced, as the tailwind component increases,
the airspeed will decrease. An increased tailwind sees to a reduction in lift, which may be
sufficient enough to cause ground collisions or induce an aerodynamic stall. Conversely, an
increased headwind can lead to aircraft overrunning the runway, as they are lifted above the
intended approach path, due to increased performance (Mulgund & Stengel, 1996).
2.1.1 EXAMPLE: Increased Tailwind with VH-NQE
This was evident with the VH-NQE hard landing incident, where the Fokker F100 had a late
touchdown (Appendix 1). Horizontal windshear had seen the forecasted 4 kt headwind have a
directional change of 180˚, strengthening into a 32 kt tailwind (ATSB, 2014). This resulted in
dramatic changes to the aircraft’s airspeed and rate of descent, causing it to touchdown
sooner than expected along the runway. Descending at 1010 FPM upon touchdown caused
the aircraft to bounce after impact with the runway, resulting in significant damage. As seen
in Table 2 of Appendix 5, the airspeed decreased from 133-110 kt over three seconds.
Comments within this same Table note that the headwind suddenly changed into a tailwind in
just one second. This would have been the point where the aircraft was passing through the
centre of the shear (NASA, 2008).
2.1.2 EXAMPLE: VH-VQT Evening Flight with Thunderstorm Conditions
Thunderstorms are associated with low-level convective windshear, which can quickly
produce adverse flight conditions without significant warning (Lankford, 2002). This was
evident with the Jetstar VH-VQT flight (Appendix 2), whose windshear encounter was
further developed with the aircraft taking off in the vicinity of a thunderstorm (ATSB, 2011),
as cumulonimbus clouds are associated with great updrafts and downdrafts (Aviation Theory
Centre, 2012). Lankford (2002) further mentions how windshear occurs in the surrounding
area of a “visible cloud system” (p. 157) due to storms obstructing air flow. Furthermore, as
this was an evening flight with forecasted thunderstorms, visibility was reduced, making it
difficult to visually foresee windshear. Windshear is also more prominent at night time, due
to less mixing of air parcels throughout the lower atmospheric layers (FAA, 2008).
2.3 Forecasting Windshear
Windshear events are difficult to detect via radar, hence few aerodromes issue Windshear
Warnings (Bom, 2014). Aerodromes will issue these forecasts if windshear is predicted to
adversely affect an aircraft’s flight path upon take-off or landing. These messages can also be
found in SPECI1 reports, for airports using manual observations received from pilots via
ATC. A range of visual cues are used for these observations, all indicating potential
conditions for windshear. Table 1 below has been modified from the BoM (2014) to list these
indicators:
Table 1 – List of External Cues for Pilot’s to Visually Detect Windshear Presence
External Cue
Comment
Strong, gusty surface winds
Particularly for aerodromes located near
hills, or where there are large buildings near
the runway
Virga from convective cloud
Downdrafts may exist and reach the ground
despite precipitation evaporating
A roll-cloud girding a thunderstorm base and Indicates the presence of a gust front
advancing ahead of the storm cell
Lenticular cloud
Associated with presence of standing waves
(smooth, lens-shaped altocumulous)
(usually downwind from a mountain)
Areas of dust raised by wind
Particularly when in the form a ring below
convective clouds (indicates downburst
presence)
Wind socks indicating winds from different
directions
Smoke plumes
Especially plumes with upper and lower
sections moving in different directions
Cumulonimbus clouds
Should assume these clouds always have
capability of producing hazardous windshear
(Adapted from: Bom, 2014, p4).
1 – SPECI: ‘special’ aviation weather report which is issued at times of significant deterioration/improvement in airport weather conditions
(BoM, 2007).
3.0 MICROBURSTS
Microbursts are the result of the high altitude air cooling quickly, due to precipitation, hence
why they are found near convective precipitation and thunderstorms. This column of cooling
air then becomes denser than the surrounding environment, causing it to sink. As the air
continues to cool rapidly, it moves downwards quickly and spreads outwards from the
column centre (Allan, 2004; Wilson, 1984). This centrifugal sinking motion produces strong
downdrafts and under cuts any warm air from rising, similarly to a frontal system
(McLennan, 2014).
3.1 Formation
The three development stages for a microburst are illustrated in Figure 1 below. During
'initial contact', the downdraft begins descending from the cloud base, developing a
downburst which rapidly accelerates down to the surface. In the 'outburst' stage, cold air
associated with the sinking downburst then causes the air parcel to "curl" outwards from the
initial contact point. Finally, the 'cushion' stage sees the curled winds have a slowed
acceleration, due to surface friction (Kentucky Wings CAP, n. d.).
Figure 1 - Microburst Genesis
(Source: Heidorn, 2005)
3.2 Effect on Aircraft Performance
Allan (2004) describes airspeed changes for aircraft encountering microbursts as "hazardous"
(p2). Microbursts affect aircraft controllability and performance, with the aircraft tending to
deviate from the desired flight path. When approaching the microburst, as seen in Figure 2,
an aircraft will experience an increasing headwind. Headwinds are preferred for aircraft
performance, so this would see to an increase in airspeed and altitude. As headwinds increase
the airflow over wings, the aircraft will have greater lift, causing it to pitch upwards. As this
wind phenomenon is difficult to detect, unaware pilots tend to correct this change in pitch by
lessening power.
Figure 2 – Flight Operation Through A Microburst
(Source: Allan, 2004).
With reference to Figure 2 once more, a continued operation through the downdraft with this
'correction' results in a loss of lift, due to the power reduction and aircraft passing through the
windshear centre, where a tailwind is then encountered. Tailwinds compromise aircraft
performance, seeing to a decrease in airspeed and further altitude loss. If the pilot continues
to operate with the reduced power setting, the aircraft becomes "vulnerable" (Allan, 2004,
p.2) and may have a compromised approach or take-off. Lankford (2002) states that
“avoidance is the best defence” (p 88) for a microburst, highlighting the importance of flight
forecast study.
3.2.1 EXAMPLE: Downdraft Affects In Flight VH-ZIC
Due to the outward flow of wind, the strongest winds associated with microbursts occur
between 500 and 1000 ft. As the outflow occurs in all directions, this can make aircraft
controllability challenging, highlighted with the VH-ZIC flight of American Blimp Group
(Appendix 3). The pilot of the airship chose to operate at a low altitude of 1000 ft, due to the
wind conditions. ATC later issued an altitude alert to VH-ZIC, as radar observations detected
the airship to be operating at 400 ft AMSL (ATSB, 2008). Observers on the ground stated
the airship was "flying very low and erratically" (ATSB, 2008, p3), which could be
associated with the aircraft passing through the strongest outflow of a microburst downdraft.
3.3 Wet and Dry Microbursts
Dry microbursts are found near high-based clouds with little precipitation whereas wet
microbursts are associated with virga cloud (Figures 5 and 6). For this reason, wet
microbursts are found in environments with high humidity and a SALR. The drag of
associated precipitation drives the microburst’s downburst acceleration. The air parcel motion
involved requires a greater mixing ratio, in comparison to dry microbursts. Further
characteristics are shown in Figure 3, where they are compared to wet microbursts.
Figure 3 – Characteristics of Dry and Wet Microbursts
(Source: Carcena, 2001)
3.3.1 EXAMPLE: Wet Microburst During Flight VH-VQT
It is likely that Jetstar’s VH-VQT Airbus entered a wet microburst (Appendix 2). This
phenomenon is “not easily dateable using conventional weather radar of windshear alert
systems” (ATSB, 2011), hence why the flight crew of VH-VQT were unable to detect the
presence of windshear and the microburst’s severe downdraft before take-off. However,
microbursts are associated with the heavy rains of a thunderstorm, so the crew could have
predicted its occurrence with visual observation, had visibility allowed.
3.5 Visual Identification of Microbursts
Wind circulation around the microburst's column centre forms a low pressure ring, with
downward motion reinforcing the downdraft and forming a peripheral updraft. As downdrafts
are associated with convective clouds, such as those leading to thunderstorms, these
conditions can see to a "precipitation curl" (Caracena, 2001), as seen in Figure 4.
Figure 4 – Precipitation Curl of a Microburst
(Source: NOAA, 2014)
Further visual cues to be noted are the cloud and precipitation conditions associated with
microbursts. Dry microbursts can be noted with the presence of a “shelf cloud” (Figure 5),
whereas virga (Figure 6) will indicate shower/thunderstorm development in a level which is
dry below but moist aloft, suggesting the presence of a wet microburst.
Figure 5 – Shelf Cloud
Figure 6 – Virga
(Source: BoM, 2015)
4.0 THUNDERSTORMS
With most flights operating in the troposphere, weather-related events such as thunderstorms
occur often during flight, possibly leading to aircraft damage and fatal accidents. During
2013 69 % of weather-related incidents during air transport operations resulted from
windshear and turbulence. An additional 26.4 % of these incidents were caused by lightning
strikes (ATSB, 2013). The BoM states that "thunderstorms are convective clouds in which
electrical discharge can be seen as lightning and heard as thunder" (BoM, 2007, p81).
Thunderstorms are associated with heavy rain, hail, strong wind gusts and lightning strikes.
Figure 7 – Supercell Storm Structure
(Source: BoM, 2007, p85)
A thunderstorm can be divided into two different cell types: normal and super (the latter cell
is depicted above in figure 7). Their difference is seen during the mature stage of
thunderstorm formation, where a supercell will maintain itself with strong vertical updrafts
and downdrafts. These drafts occur from frictional drag by precipitation particles, as seen in
figure 7 (BoM, 2007, p91 and Rotunno, 1985). This causes high turbulence around the
thunderstorm, with a lifting mechanism producing more cumuli cloud. Supercells are also
larger, having a 10-40 km cloud base compared to 5-10 km for a normal cell (BoM, 2007,
p81).
4.1 Formation of a Thunderstorm
The formation of a thunderstorm comes down to cloud formation, where the atmosphere is
moist and unstable. The BoM outlines a cloud as "a visible aggregate of tiny water droplets
and/or ice crystals suspended in the atmosphere and can exist in a variety of shapes and sizes"
(BoM, 2007, 31). Clouds are formed when an air parcel reaches saturation, which can be
achieved through convection2, orographic Lifting3 or when air is forced upwards by warm or
cold fronts (BoM, 2007, 31). As the air parcel is cooled and reaches the dew point
temperature, saturation occurs. If the air parcel is warmer than the environment and
condensation occurs, a cumuliform cloud is produced (BoM, 2007, p31).
A towering cumulus cloud, which is the initial stage of a thunderstorm (refer to part A of
figure 8), is formed when there is significant unstable air and strong updrafts. The strengths
of the updrafts at this stage range from 2000-4000 FPM, which is stronger than ordinary
convection. This gives the cloud opportunity to grow in a vertical motion where there are
significant rain and ice crystals suspended throughout.
Figure 8 – Formation of a Thunderstorm
(Source: BoM, 2007, p84).
2 – Convection: when air that is warmer than its environment starts to rise due to the high pressure near the ground and low
pressure above
3 – Orographic Lifting: when air is forced upwards due to terrain, and widespread ascent
(Source: BoM, 2007, p31)
The second stage is the mature stage of the thunderstorm (part B of figure 8). At this point,
precipitation starts to fall and the updraft has grown in intensity to 8000-10000 FPM, it is
strongest at the upper levels of the cloud. The anvil like structure can be seen in this stage as
the cloud's top reaches comes in equilibrium (i.e. the saturated temperature has become the
same as the environment). During the dissipating (final) stage, the downdrafts spread out and
cut off the supply of any updrafts. This means that the thunderstorm is no longer receiving
warm, moist air (BoM, 2007, p84).
4.2 Lightning Formation
Lightning forms when water droplets and ice crystals, found in cumulus clouds, create static
friction by rubbing together. This in turn creates and electrical charge. The positive charges
are found at the top of the cloud with the negative charges located at the bottom or on the
ground. When the separation between these charges is large enough, the cloud releases
energy, producing a lightning strike (BoM, 2007, p98 & Tega, 2010).
4.3 Effects of Lightning Strikes on Aircraft
Lightning strikes can have devastating effects on an aircraft’s structural integrity and
instrument performance. As an aircraft operates through a heavily charged region of cloud, it
is susceptible to a lightning strike. Upon strike, the lightning will connect with any protruding
edge such as an aircraft’s nose or wing. As aircraft are made of aluminium, a highly
conductive material, the lightning follows this conductive skin and usually exits through the
aircraft’s tail (Fankhauser, 1971 and Rupke, 2006). Lightning strikes also have the capability
to travel through the external skin to wires and equipment which may cause the instruments
to surge and stop working (Broc, 2006). Modern day aircraft are engineered to limit the
chances of internal surges through shielding, grounding and various surge protectors (Rupke
2006 and Williams, 2014).
4.3.1 EXAMPLE: VH-LBC Lightning Strike Accident
The effects discussed in section 4.3 are highlighted in the VH-LBC accident (Appendix 4),
involving a Cessna 441, where the aircraft was struck by lightning on the left wing tip.
Although the avionics and electrical system were still operational, there was substantial
damage to the elevators and propellers (ATSB, 2008).
4.4 Identifying and Forecasting for Thunderstorms
Prior to conducting a flight, pilot’s must observe weather patterns and study relevant weather
charts in case of dangerous weather phenomenon existing. There are many tools that a pilot
can use to obtain this information such as visual cues, Area Forecasts (ARFOR), Aerodrome
Forecasts (TAF), Trend Forecasts (TTF), all of which can be retrieved from the Bureau of
Meteorology website or Air Services Australia (NAIPS).
4.4.1 ARFOR
ARFOR show forecasts within Australia for operations at or below 20,000 feet (Lee, 2015,
Week 2). Appendix 6 shows how Australia is divided into 28 sectors, each having their own
ARFOR for that specific area. An ARFOR example is provided in Appendix 7, which shows
an amended forecast for Area 20 from 0015 27/04/2015 to 1100 27/04/2015 UTC time (valid
from 1015 to 2100 EST). Refer to Appendix 8 for an explanation of these time conversions.
Specific codes within the ARFOR are provided for pilot’s to understand the amount and type
of cloud present, as well as associated weather conditions (Appendices 7 and 9). Cloud types
such as cumulus, cumulonimbus and towering cumulus clouds, associated with
thunderstorms, are given the abbreviation of CU, CB and TCU respectively. The amount of
CB cloud is described with additional cloud amounts, such as ISOL for “isolated” (Appendix
9, Figures 10, 11 and 12) (Lee, 2015, Week 3).
ARFORs also provide further abbreviations for weather related events to describe local cloud
conditions. Figure 9 of Appendix 9, highlights some abbreviated weather events such as
thunderstorms (TS) and rain (RA). When put together, the term ‘TSRA’ indicates
thunderstorms with rain.
Using the ARFOR in Appendix 7, it forecasts isolated TS out at sea, south of Coffs Harbour,
with isolated cumulonimbus cloud at 3000 ft and 30000 ft AGL. Showers with rain and
thunderstorms with rain can be expected south of Coffs Harbour, with severe turbulence
found in CB. Based on this information, a pilot can foresee dangers of flying in this area with
such thunderstorm conditions.
4.4.2 TAF
TAFs show related weather within a 5 nm radius of an aerodrome's reference point (Lee,
2015, Week 3). A pilot should obtain a TAF for the Aerodrome they are departing and one
for the arrival point with respected to the estimated time of arrival. Appendix 10 shows a
TAF for Sydney and one for Coffs Harbour valid from 26/04/2015 2317 UTC (0917 EST).
TAFs are issued every six hours and are valid for a minimum of 12 hours (Lee, 2015, Week
3). Based on the information given in Appendix 10, there are no thunderstorms present within
the radius of either aerodrome, with the only significant weather in Sydney being few clouds
at 2500 feet AGL, but from the 28/04/2015, cloud increases to scattered at 0000 UTC (1000
EST). Coffs Harbour has CAVOK conditions, meaning there is:

visibility of 10 km or more

no significant cloud below 5000 ft

no significant weather (Lee, 2015, Week 3)
As the TAF is forecasted for a minimum of 6 hours, the pilot can easily foresee that the
thunderstorms are too far off shore to affect a normal flight route from Sydney to Coffs
Harbour after 0917 EST.
4.4.3 TTF
TTFs are specific for major aerodromes and are valid for three hours. This forecast replaces
the TAF for the period upon the time of observation (Lee, 2015, Week 3). Appendix 11
shows a TTF for Sydney at a time of 0200 UTC, outlining that conditions are CAVOK.
Another tool that a pilot can use is the BoM radar. Appendix 12 shows the radar for the
Sydney area as at 0154 UTC (1154 EST). It can be seen that the thunderstorm is far east,
which will not affect the flight. Comparing this to Appendix 13, displaying the radar for
Williamtown area North of Sydney, a thunderstorm is seen at 01/05/2015 0154 UTC (1154
EST). A pilot should avoid this area whilst also retrieving the appropriate forecasts (TAF,
TTF, ARFOR) for the specific flight.
5.0 CONCLUSION
This report has outlined the meteorological conditions associated with windshear and
microbursts, and also thunderstorms and lightning. The various effects that these phenomena
have on aircraft were identified. It was found that windshear is particularly hazardous to
operations within close proximity to airports, having the greatest impact for flights taking-off
or landing. Microbursts and associated windshear can see headwinds change into tailwinds,
reducing aircraft performance. Lightning strikes may cause structural damage to the aircraft
and internal damage such as power surges, affecting flight instruments. It was argued that a
pilot should always forecast prior to flight using appropriate methods such as visual cues and
forecast charts (ARFOR, TTF, TAF). Using these methods will increase the pilot’s awareness
of meteorological conditions throughout their flight.
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Broc, Alain. (December 2006). A Lightning Swept Stroke Model: A valuable tool to investigate
the lightning strike to aircraft. Aerospace Science and Technology, 10(8), pp 700 – 708.
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Bureau of Meteorology. (2015). Storm Spotters’ Handbook: Observing thunderstorms.
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Bureau of Meteorology. (2015). Aerodrome Forecasts (TAF),
http://www.bom.gov.au/aviation/forecasts/taf/
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Appendix 1 – Summary for Flight with Windshear Incident
VH-NQE
The Fokker F100 was approaching Nifty Aerodrome (Western Australia), where "high-based
cumulous cloud and isolated thunderstorms" (ATSB, 2014, p3) had been forecasted. Upon
descent during final1, the airspeed decreased dramatically from 133 kt to 110 kt over just
three seconds, as shown in Table 2 of Appendix 5. The rate of descent increased to 1000
FPM, resulting in the aircraft landing hard on the threshold (300 m before the usual runway
touchdown). This dramatic speed reduction and increased rate of descent occurred as the
F100 entered the strong "outflow" (ATSB, 2014, p3) of a dry microburst.
Significant damage was caused as a result of the aircraft bouncing after touchdown,
combined with the effects of a 32 kt tailwind.
The ATSB found the aircraft was not fully capable to recover from the event as the F100 was
not configured for approaches in windshear conditions. The aircraft's low altitude also left
insufficient time for a windshear warning system to be sounded. Referring to Appendix 3
once more, the EGPWS (Early Ground Proximity Warning System) “Sink Rate” warning was
transmitted, but with an altitude of just 15 ft, it was too late for the flight crew to respond to
this. If time had allowed, this warning would have changed into “Pull Up”, prompting pilots
to exit their steep descent (Allied Signal, n. d.).
Appendix 2 – Summary of Windshear Encounter During Flight
VH-VQT
In October 2010, a Jetstar A320-232 aircraft experienced a windshear incident upon departed
from Darwin Airport (Australian Transport Safety Bureau, 2011). The flight crew had noted
local thunderstorm activity was forecasted, but no thunderstorm cells were observed to be
within 5 nm of the airfield. Further observations by the Captain during taxi via the on board
weather radar provided no storm cell indications in the local area. Despite these observed
results, the aircraft encountered an abrupt wind change whilst accelerating into a 5 kt
headwind for take-off, at around the rotation speed (the speed where an aircraft is committed
to take-off and should begin climbing (SKYbrary, 2014)). This incident coincided with the
sudden onset of torrential rain, reducing visibility. Lastly, a tailwind was encountered shortly
after take-off, with a wind gust during the windshear event.
Appendix 3 – Summary of Microburst Flight Incident
VH-ZIC
The airship pilot contacted BoM for a weather briefing and was told conditions were likely to
be windy. This forecast was later amended to report on an 18 kt wind with a gust factor of 35
kt (also moderate turbulence below 5000 ft). After departure approximately five hours later,
the airship was reported to be "flying very low and erratically" (ATSB, 2008, p3)
Viewers observed the airship "pitching rolling and yawing while being buffeted by the wind"
(ATSB, 2008, p4).
OCNL sev turbulence had been forecasted for the lee side of mountain ranges on the north
side of Melbourne.
Appendix 4 – Summary of Lightning Strike Accident
Flight VH-LBC
At around 1830 in February of 1997, the Cessna 441 aircraft was operating near Mount
Magnet, in Western Australia. The pilot was operating at FL310 and reported himself as
being clear of the cloud level when the aircraft encountered a lightning strike. Upon striking
the aircraft, the pilot noted "a large flash and a loud bang followed with an ozone smell"
(ATSB, 2008, p3). After being struck on the left wing tip, the pilot chose to continue the
planned flight into Perth as the avionics and electrical systems did not appear to be affected.
Once landed, the aircraft was inspected on the ground, with notable damage found on the
elevators and propellers.
Appendix 5 – Recorded Events Relating to Airspeed and Descent Rate for VH-NQE
Table 2 – Sequence of Events During Flight VH-NQE
(Source: ATSB, 2014, p7).
Appendix 6 – Sectors of Australia for Which ARFORs are Issued
(Source: BoM, 2014, ARFOR)
Appendix 7 – ARFOR Example (Using Area 20: Sydney Region)
(Source: BoM, 2015).
Aerodromes are given a four letter abbreviation code starting with 'Y'. The second letter
represents the telecommunication centre that the controlled aerodrome is linked with. The
remaining two letters is an abbreviation of the location such as YSSY as Sydney Airport,
YBBN as Brisbane Airport (Lee, 2015, Week 3).
Appendix 8 – Time Conversions for UTC (Zulu) Time
(Source: Airservices Australia, n.d.)
Appendix 9 – Abbreviated Codes Used for ARFOR Weather Descriptions
Figure 9 – List of Abbreviations for Descriptions Used in an ARFOR
Figure 10 – Abbreviated Codes for
Cloud Types
Figure 11 – Codes for Overall
Cloud Coverage
Figure 12 – Codes for Cloud
Amount
(Describing cumulonimbus (CB) cloud
only)
(Source: BoM, 2015, ARFOR)
Appendix 10 – TAF for Sydney and Coffs Harbour Areas
(Source: BoM, 2015, TAF).
(Source: BoM, 2015, TAF).
Appendix 11 – TTF for Sydney Area
(Source: BoM, 2015, TTF)
Appendix 12 – BoM Radar Loop for Sydney Area
(Source: BoM, 2015, 128 km Sydney (Terrey Hills) Radar Loop)
Appendix 13 – BoM Radar Loop for Williamtown
(Source: BoM, 2015, 128 km Newcastle Radar Loop)

windshear, microbursts, thunderstorms and

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