Amateur Build Safety

Why Is My Airplane Trying To Kill
Me?
A Presentation on Homebuilt Aircraft Safety
By
Will Fox, CFI, TC, FA
Email: [email protected]
2/16/14
Page 1
Risk Triple Distillation Theory
!
Pilots, in general, are willing to
accept a higher level of risk than
much of the population
– 1 in 500 people in the US are pilots.
!
Homebuilt pilots are willing to
accept a higher risk than pilots of
certified aircraft.
– Homebuilt aircraft have a fatality rate that
is 3 times greater than comparable
certified aircraft.
!
Pilots who test fly homebuilt
aircraft are willing to accept a still
higher risk during initial testing.
– The accident rate in Phase I testing is 5
times greater than in Phase II operation .
!
!
One might infer that this process
results in a triple distillation of risk
tolerance.
Homebuilder/pilots should be
aware of this and consider ways
to mitigate the risks they accept.
2/16/14
Page 2
Why Is My Airplane Trying To Kill
Me?
!
!
!
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Homebuilt safety Myths
What are the accidents telling us?
What can we do to improve the safety of homebuilt aircraft?
Homebuilt Aircraft Safety Score
2/16/14
Page 3
Homebuilt Safety Myths-Part I
!
!
Myth #1: Homebuilt aircraft are
just as safe as GA aircraft.
Truth: Fatal accidents occur
about 3 times more often than in
similar GA aircraft on a per hour
of operation basis. Homebuilt
aircraft can also have less
forgiving flight characteristics
particularly with regard to
stall/spin behavior.
Myth #2: Auto engines can be
just as reliable as aircraft engines
and a lot cheaper. Truth: Auto
engines converted for aircraft use
fail at a significantly higher rate
than traditional aircraft engines
and often require more
maintenance. When all the costs
are considered, the cost of
traditional aircraft engines and
auto conversion engines are
more competitive than most
people think.
2/16/14
Page 4
Homebuilt Safety Myths-Part II
!
!
Myth: Homebuilts are built out of
modern material like fiberglass and
carbon composite and therefore are
stronger in a crash. Truth:
Composite materials can be quite
strong, but they have many times less
ductility than the equivalent steel or
aluminum structure and therefore are
less able to absorb energy and
mitigate impact loads in a crash
unless specifically designed to do so.
Composites break, metals bend.
Myth: You will have to give up
performance to improve the safety of
homebuilts. Truth: Crashworthiness
is an aspect of performance as well,
and one that can save your life.
Improving safety doesn’t mean that
you have to give up performance in
other areas. The Bonanza, which is
noted for its performance
characteristics, has a cabin designed
for impact loads up to 25 gs. The
Cirrus, another high performance
aircraft, has a seat designed to crush
in a graded manner to allow the
occupants to survive much higher
vertical speed impacts.
2/16/14
Page 5
Increase in Homebuilt Accident Rate
Acknowledged By EAA in April 2009
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April 2009 EAA issued a Safety Wire
News article to Flight Advisors and
Technical Counselors about increasing
accident rates for homebuilt
(Experimental Amateur Built - EAB)
aircraft.
The EAA and the FAA were becoming
concerned with the deteriorating safety
record for EAB aircraft,
The accident rate for Amateur built
aircraft increased by 40% from 20042007.
The accident rate for AB aircraft in 2008
was 3.5 times greater than personal use
General Aviation aircraft.
High performance AB aircraft such as
the Lancair and Vans RV are having a
disproportionate amount of accidents.
2/16/14
Page 6
NTSB Issues EAB Safety Study In
May 2012
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!
!
The NTSB is concerned about EAB
aircraft safety and conducts a study to
compare EAB aircraft and non-EAB
aircraft safety in May 2012.
The study indicates that EAB aircraft
have three times the fatality rate of nonEAB aircraft.
The study is composed of four major
elements.
– Comparison of EAB to Non-EAB accidents
for the past 10 years.
– In-depth investigation of all EAB accidents in
2011.
– Analysis of EAA Survey data.
– Discussions between NTSB,FAA, EAA, kit
manufacturers, and EAB builders and
owners.
!
They come up with 12
recommendations for the FAA and 4
recommendations for the EAA.
2/16/14
Page 7
EAB Aircraft Crash Twice as Often
As Non-EAB Aircraft
!
Based on a study by the NTSB that compared Experimental Amateur Built (EAB)
aircraft which were represented by single engine, piston powered, amateur built
aircraft (fixed wing, helicopter, balloons, gliders, and gyroplanes) to Non-EAB
aircraft that were similar type aircraft but composed of standard category and light
sport aircraft, the following observations can be made:
– EAB aircraft crash about twice as often as Non-EAB aircraft both on a fleet basis and on an
hours flown basis.
– EAB aircraft crashes are much deadlier than non-EAB aircraft, because fatalities occur
50% more often when a crash does occur.
2/16/14
Page 8
Loss Of Control In Flight and Powerplant
Failures Cause Most EAB Accidents
!
!
!
Almost 60% of fatal EAB
aircraft accidents are due
to two things, Loss of
Control in Flight and
Powerplant Failures.
By comparison, these
same two categories
represent 45% of Non-EAB
aircraft fatal accidents.
Non-EAB aircraft, however,
have a much higher
accident rate than EAB
aircraft when it comes to
weather related accidents.
2/16/14
Page 9
The Pilot is the Most Important Safety
Device in the Plane, But They Need Help
!
!
!
!
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About 75% of the aircraft
accidents that occur are
attributed to Pilot Error in
one way or another.
The aviation community
has been trying to solve
this problem in the General
Aviation sector for many
years with limited success.
Pilots don’t go out and
crash planes on purpose.
They are human and
therefore subject to error.
The question is not how do
we completely eliminate
human error, but rather,
how can we mitigate the
consequences when it
occurs.
2/16/14
Page 10
Two Of The Most Important Things You
Can Do to Avoid An Accident
!
!
Improve your stall warning equipment and your stall/spin awareness.
Make your propulsion system as reliable as you can.
2/16/14
Page 11
Loss of Control In Flight Accidents Are
Dominated By Stalls And Spins
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!
!
!
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Rich Stowell1 states that 45% of the
homebuilt fatal accidents are preceded
by a stall or a spin.
Many homebuilt aircraft have no stall
warning device and no appreciable
aerodynamic buffeting prior to a stall.
Some homebuilt aircraft exhibit abrupt
stall behavior and stall asymmetrically,
resulting in a spin entry.
Stalls such as these may require
hundreds or even thousands of feet to
recover from.
Because the stall or spin is a surprise,
initial pilot responses often aggravate
the stall or spin.
1. Rich Stowell’s Book - The Light Airplane Pilot’s Guide to Stall/spin Awareness
2/16/14
Page 12
How Can We Prevent Stall/Spin
Accidents?
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!
!
!
Install a Stall Warning or Angle
of Attack (AOA) device in your
Homebuilt.
Implement stick shakers and
automatic stall prevention or
recovery systems.
Improve the stall characteristics
of existing aircraft with:
– Vortex generators
– Stall fences
– Stall trip devices
Design more “Spin Resistant”
aircraft using NASA technology
– Discontinuous leading edge cuffs
– Stall control wing slots
– Slats
2/16/14
Page 13
Effectiveness of Stall Warning Devices
!
According to several FAA studies:
– Stick Shakers are by far the most
effective stall warning device.
"
Pilots responded 99% of the time with
an average response time of 1.1
seconds.
– Interrupted stall horn was second
best stall warning device.
"
Pilots responded 85% of the time with
an average response time of 1.5
seconds.
– Continuous stall horn was the third
best stall warning device.
"
Pilots responded 64% of the time with
an average response time of 1.7
seconds.
– Pilots prefer and respond better to
stick shakers and even aerodynamic
buffeting than aural stall warnings.
– AOA indicator used in conjunction
with a stall horn or Stick Shaker were
found to be the most effective.
– Stall lights are the least effective.
2/16/14
Page 14
Powerplant failures Cause About 1 out
of 4 Homebuilt Aircraft Accidents
!
!
!
!
The NTSB found that 23% of the
EAB accidents were caused by
powerplant failures versus 14%
for Non-EAB aircraft.
Ron Wanttaja2 found that about
13% of the accidents involving
fixed-wing homebuilts with
traditional powerplants were due
to engine failures, versus over
35% for aircraft with auto
engines.
The most likely failures in Auto
Engine Conversions were
ignitions and cooling systems and
the reduction drive system.
In the accidents that resulted
from builder errors, 1/3 were due
to fuel system problems and
another 30% were due to builder
mistakes with the engine or drive
line.
2. Ron Wanttaja - Homebuilt Aircraft Safety 1998-2006
2/16/14
Page 15
How Can We Prevent Aircraft
Powerplant Failures?
!
!
!
!
Conduct Fuel Flow testing.
Encourage the use of proven aircraft
engines in homebuilts.
Increase the use of EAA Technical
Counselors and A&Ps with regard to
inspection of fuel systems and firewall
forward installations.
Educate homebuilders about important
measures of engine performance and
longevity, and encourage nontraditional aircraft engine builders to
publish relevant reliability data and
maintenance requirements for aircraft
engines so homebuilders can make
intelligent choices.
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–
–
–
!
Mean Time Between Failure (MTBF)
Time Between Overhaul (TBO)
Brake Mean Effective Pressure (BMEP)
Mean Piston Speed (MPS)
Offer lower insurance rates to
homebuilders who use more reliable
and proven engines.
2/16/14
Page 16
Homebuilt Aircraft Are Not Especially
Crashworthy
!
!
It is difficult to find data on the
crashworthiness of homebuilt
aircraft, but we can make a few
observations.
Many homebuilts do not exhibit
crashworthy features such as:
– Cabins designed to protect occupants
–
–
–
–
–
–
!
that include roll cages.
Cabins that remain intact following an
impact.
Seats designed to limit impact loads.
High integrity restraint systems.
Engine locations that are not
hazardous.
Fuel storage outside of the cabin.
Firewall and engine cowl designs that
resist nose-overs.
One might observe that
crashworthiness is not a key
consideration in most homebuilders’
minds, since it is not typically part of
a homebuilder’s purchase decision,
nor a feature advertised by kit
manufacturers.
2/16/14
Page 17
What Can We Learn From Very
Crashworthy Aircraft - Crop Dusters?
!
!
Experts agree that 85% to 90% of
all aircraft crashes can be
survivable with incorporation of
crashworthiness features.
Let’s look at features in an aircraft
where crashworthiness is one of
the most important performance
characteristics - A Crop Duster.
– Internal steel roll cages
– Large amount of structure (engine
and hopper) in front of pilot to absorb
impact forces.
5 point restraint system
Energy-absorbing landing gear
Self-sealing fuel tanks and lines
14g collapsible seats
Wire cutters
Helmets
!
–
–
–
–
–
–
All of the pilots in the pictures
shown to the right of crop duster
crashes survived, and most had
little or no injury.
2/16/14
Page 18
There Is A Substantial Knowledge Base For
The Design Of Crashworthy Aircraft
!
The AGATE Small Airplane
Crashworthiness Design Guide has
much to offer in terms of how to design
more crashworthy aircraft.
–
–
–
–
–
!
!
Crash Physics
Biometrics
Airframe and Seat Crash Resistance
Restraints Systems
Delethalizing Interiors and more
AGATE establishes test conditions for
survivable impacts.
AGATE provided design goals for the
cabin structure that would make aircraft
accidents much more survivable.
2/16/14
Page 19
Stall Speed Is Important To Making
Homebuilt Crashes More Survivable.
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!
!
!
Stall Speed strongly effects the
amount of energy that has to be
absorbed in a crash. There is 4
times the energy to dissipate at
60 kts as there is at 30 kts.
Light aircraft with stall speeds
less than 45 knots have high
crash survivability.
Light aircraft with stall speeds
greater than 75 knots have
almost zero crash survivability.
The FAA mandated a maximum
stall speed of 61 knots for
certified aircraft less than 6000
lbs to improve crash
survivability.
Crash survivability plot by by Barnaby Wainfan from
“Wing Design: Major Decisions” presentation
2/16/14
Page 20
A Fire Following A Crash Is A Very
Deadly Event
!
Your chances of surviving a fire following an
aircraft crash are very low.
– In 1998, a safety analysis of 68 GA aircraft
accidents revealed that 22 pct of the crashes
involved post-crash fire. Forty-eight pct of the
occupants in these accidents were fatally injured3.
– The crash scenarios evaluated in the study were
selected to approximate the limits of survivability,
and the statistics obtained from their analysis
suggest that although there are not a large number
of GA aircraft crashes involving post-crash fire, the
accidents that do involve fire are extremely lifethreatening for the occupants.
!
!
!
!
Modern light aircraft designers avoid storing
fuel in the cabin area. They also seek to
protect fuel lines and fuel selector valves in
the event of a crash.
Crop dusters use self-sealing fuel tanks and
lines.
Recently, Robinson Helicopter Co. began
installing self-sealing tanks in their helicopter,
because the occupants were being killed by
fire far more often than by the crash impact.
Avoid installing fuel tanks in front of the cabin
and in front of the spars of the wings where
they are likely to be damaged in crash.
3. Chapter 10 of the AGATE Small Airplane Crashworthiness Design Guide.
2/16/14
Page 21
Four Things You Can Do To Improve
Your Homebuilt’s Crashworthiness
!
!
!
!
!
Provide 4 or, better yet, 5 point
restraints systems for all occupants.
Use inertial reels on shoulder
harnesses.
Eliminate sharp edges in the cabin and
use energy absorbing materials on
potential impact zones.
Use fireproof or fire resistant materials
for the interior.
Big Tires:-)
2/16/14
Page 22
Some Crashworthy Features To Look
For In A Homebuilt
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Excellent stall behavior and spin resistant
features.
Engines designed for aviation applications.
Cabins with roll cages and with safe flail
zones that are designed to protect occupants
up to the AGATE guidelines.
Seats that are designed to remain attached to
the cabin structure and to attenuate impact
decelerations based on the AGATE
guidelines.
Firewalls and Fuselage design features that
are designed to resist “digging-in” and noseovers.
Fuel that is stored outside and away from the
cabin and fuel tanks that are crash resistant
or even incorporate self sealing bladders.
Controls that are located to the side of the
occupants.
Multiple egresses for emergencies.
Seat belt pretensioners.
Airbags.
2/16/14
Page 23
We Can Make Your Homebuilt Safer
- A Lot Safer !
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!
!
!
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Given the innovativeness shown by the
homebuilt community, there is great
opportunity for improving Homebuilt Safety.
The knowledge and technology exist already.
We just need to apply them.
Communicating the facts is extremely
important, so builders know what is safe and
what isn’t, so they know where to apply their
energies to make their aircraft safer.
Safe aircraft do not have to have lower
performance. Look at the stall characteristics
of the Questair Venture, or the cabin integrity
of a Bonanza, or the seat design of a Cirrus.
Safe aircraft do not have to be expensive
aircraft. The cost of quadrupling the crash
survivability of cars over the last 30 years, was
only about 1/15 of the price of the car (about
$1500 for $22,000 car)4.
There is no reason to believe that we can’t
accomplish as much in homebuilt aircraft. Try
to imagine how much better you and your
passengers would feel flying an aircraft that is
four times safer than most other GA aircraft - it
would be great!
It is not only doable, but it is also the right thing
to do.
4. Daniel Sperling, “The Price of Regulation, Fall 2004
2/16/14
Page 24
Homebuilt Aircraft Safety (HAS) Score
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Wouldn’t it be great if we had a way to score a
homebuilt aircraft on safety?
We should be able to, by considering the safety
features that we have been discussing.
We know that stall speed, spin resistance, and
engine reliability are important, as well as the
crashworthiness of the cabin, seats, restraints, and
other features.
We should be able to evaluate to what degree a
homebuilt incorporates these features, and by
weighting them appropriately, come up with a
scorecard.
The next ten slides show you some examples of
how to do that and to come up with a Homebuilt
Aircraft Safety Score (HASS).
If we do it right, there should be some correlation
between the HAS score and the likelihood of an
accident being fatal for a particular type of aircraft.
I picked eight aircraft for assessment:
"
RV-7/7A
"
Lancair IV
"
Sonex
"
Zenair 701
"
Varieze
"
Cessna 172
"
Questair Venture
"
Pegazair
Zenair 701 Survivable Accident
Percentage - 89%
HAS Score=125
Varieze Survivable Accident
Percentage - 73%
HAS Score=85
RV-7/7A Survivable Accident
Percentage - 65%
HAS Score=80
Lancair IV Survivable Accident
Percentage - 49%
HAS Score=40
2/16/14
Page 25
Homebuilt Aircraft Safety Score
1- Stall Speed
Stall speed (60 points)
A. Stall speed 31 knots or less – 60 points.
B. Stall speed 41 knots or less – 35 points.
C. Stall speed 51 knots or less – 20 points.
D. Stall speed 61 knots or less – 15 points.
E. Stall speed 71 knots or less –10 points
F. Stall speed over 71 knots - 0 points.
"
"
"
"
"
"
"
"
RV-7/7A -20 points
Lancair IV - 0 points
Sonex - 35 points
Zenair 701 - 60 points
Varieze - 15 points
Cessna 172 - 20 points
Questair Venture - 15 points
Pegazair - 60 points
2/16/14
Page 26
Homebuilt Aircraft Safety Score
2 - Stall/Spin
"
"
"
"
"
"
"
"
Aircraft Stall/Spin Characteristics (40 points).
A. Spin proof. The aircraft will not enter a
spin - 40 points.
B. Spin resistant. The aircraft resists
entering a spin The aircraft resists entering a
spin as prescribed by FAR Part 23 - 30
points.
C. Acceptable stall/spin behavior. The
aircraft has docile stall characteristics and
clear aerodynamic warning; a stall warning
device; effective ailerons in a stall; sufficient
rudder to level wings in a stall and to recover
from an incipient spin with a minimum
altitude loss (<1000 ft) – 10 points.
D. Poor Stall/spin behavior. The aircraft has
abrupt stall characteristics with little or no
warning; ailerons are ineffective during a
stall; aircraft is not recoverable from a spin
or requires excessive altitude to recover from
an incipient spin (>1000 feet) – 0 points.
RV-7/7A - 10 points
Lancair IV - 0 points
Sonex - 10 points
Zenair 701 - 30 points
Varieze - 30 points
Cessna 172 - 10 points
Questair Venture - 10 points
Pegazair - 30 points
2/16/14
Page 27
Homebuilt Aircraft Safety Score
3 - Cabin Structure
Cabin Structure (20 points).
A. Meets or exceeds AGATE Preferred
Cabin structural load factors and survivable
volume requirement. The aircraft has
multiple exits and resists nose over - 20
points.
B. Meets the AGATE Minimum Cabin
structural load factors and survivable
volume requirement. The aircraft resists
nose over – 15 points.
C. Meets the FAR Part 23 Emergency
Landing Conditions but does not meet a
specified survivable volume requirement or
occupant deceleration limit – 10 points.
D. Cabin structure does not meet any
recognized standard for crashworthiness - 0
points.
"
"
"
"
"
"
"
"
RV-7/7A - 10 points
Lancair IV - 0 points
Sonex - 10 points
Zenair 701 - 0 points
Varieze - 0 points
Cessna 172 - 15 points
Questair Venture - 10 points
Pegazair - 0 points
2/16/14
Page 28
Homebuilt Aircraft Safety Score
4 - Restraint System
"
"
"
"
"
"
"
"
Restraint System for all occupants (20
points).
A. 4 or 5 point restraint
system. Satisfies the AGATE
Preferred 26g forward
deceleration requirement.
Incorporates inertia reels and
airbags - 20 points.
B. 4 point restraint system.
Satisfies the AGATE Minimum
9g forward deceleration
requirement. Incorporates
inertia reels - 10 points.
C. 3 point restraint system – 5
points.
D. 2 point restraint system – 0
points.
RV-7/7A -10 points
Lancair IV - 5 points
Sonex - 10 points
Zenair 701 - 5 points
Varieze - 10 points
Cessna 172 - 5 points
Questair Venture - 5 points
Pegazair - 10 points
2/16/14
Page 29
Homebuilt Aircraft Safety Score
5 - Powerplant
"
"
"
"
"
"
"
"
Powerplant (15 points).
A. Aircraft uses a traditional
aircraft engine such as a Lycoming,
Continental, or Clone. Aircraft uses
a propeller by a major manufacturer
such as Hartzell or McCauley.
Aviation rated components are used
firewall forward – 15 points.
B. Aircraft uses a Rotax four stroke
engine. Aircraft uses a propeller
tested and manufactured to a
recognized certification standard –
10 points.
C. Aircraft uses an engine and
propeller designed for aircraft
applications that has been tested and
manufactured to a recognized
certification standard – 5 points.
D. Auto conversion or 2-stroke
engine or propeller that has not met
any recognized certification standard
– 0 points.
RV-7/7A -15 points
Lancair IV - 15 points
Sonex - 5 points
Zenair 701 - 5 points
Varieze - 15 points
Cessna 172 - 15 points
Questair Venture - 15 points
Pegazair - 15 points
2/16/14
Page 30
Homebuilt Aircraft Safety Score
6 - Seats
"
"
"
"
"
"
"
"
Seats (15 points).
A. Seats meet AGATE Preferred
Structural Load Factors or new FAR
Part 23 (26 g forward, 16.5 g
downward and 4.5 g sideways).
Seats incorporate energy absorption
device to limit impact loads. Seats or
restraint system designed to prevent
submarining - 15 points.
B. Seats meet AGATE Minimum
Structural Load Factors or old FAR
Part 23 requirements (9 g forward, 6
g downward and 1.5 g sideways).
Seats or restraint system designed to
prevent submarining - 5 points
C. Seats do not meet AGATE or FAR
Part 23 design or test requirements 0 points
RV-7/7A - 0 points
Lancair IV - 0 points
Sonex - 0 points
Zenair 701 - 0 points
Varieze - 0 points
Cessna 172 - 5 points
Questair Venture - 0 points
Pegazair - 0 points
2/16/14
Page 31
Homebuilt Aircraft Safety Score
7 - Cockpit Protrusions
"
"
"
"
"
"
"
"
Cockpit protrusions (10 points).
A. Cockpit is padded to
protect occupants from
impact injuries. Collapsible
control columns or offset
controls are used. Cockpit
has no protrusions or all
protrusions are padded – 10
points.
B. Cockpit has protrusions,
and controls represent
impact hazards– 0 points.
RV-7/7A - 0 points
Lancair IV - 10 points
Sonex - 0 points
Zenair 701 - 10 points
Varieze - 10 points
Cessna 172 - 10 points
Questair Venture - 10 points
Pegazair - 10 points
2/16/14
Page 32
Homebuilt Aircraft Safety Score
8 - Fuel System
"
"
"
"
"
"
"
"
Fuel System (5 points).
A. Fuel flow system uses
one fuel selector valve and
meets fuel flow
requirements of AC90-89A
– 5 points
B. Fuel flow system uses
multiple fuel selector
valves or does not meet fuel
flow requirements of
AC90-89A – 0 points.
RV-7/7A - 5 points
Lancair IV - 5 points
Sonex - 5 points
Zenair 701 - 5 points
Varieze - 5 points
Cessna 172 - 5 points
Questair Venture - 5 points
Pegazair - 5 points
2/16/14
Page 33
Homebuilt Aircraft Safety Score
9 - Fire Resistance
"
1) Fire resistance (5 points)
A. No fuel storage in the
cockpit. Fire resistant
materials used for the
interior. Fuel lines are fire
sleeved or metal– 5 points.
B. Fuel stored in the
cockpit. Fuel lines are not
fire resistant. Interior is
constructed of materials that
aren’t fire resistant – 0
points.
RV-7/7A - 5 points
Lancair IV - 0 points
Sonex - 0 points
Zenair 701 - 5 points
Varieze - 0 points
"
Cessna 172 - 5 points
"
"
"
"
"
"
Questair Venture - 5 points
Pegazair - 5 points
2/16/14
Page 34
Homebuilt Aircraft Safety Score
10 - Engine Location
"
"
"
"
"
"
"
"
Engine location (5 points)
A. Engine in front of the
pilot – 5 points.
B. Engine behind the pilot
with no appreciable crash
mitigation features– 0
points.
RV-7/7A - 5 points
Lancair IV - 5 points
Sonex - 5 points
Zenair 701 - 5 points
Varieze - 0 points
Cessna 172 - 5 points
Questair Venture - 5 points
Pegazair - 5 points
2/16/14
Page 35
Homebuilt Aircraft Safety Score
Observations
!
Total Score (out of 195 points
possible):
"
"
"
"
"
"
"
"
!
!
!
RV-7/7A -80 points
Lancair IV - 40 points
Sonex - 80 points
Zenair 701 - 125 points
Varieze - 85 points
Cessna 172 - 95 points
Questair Venture - 80 points
Pegazair - 140 points
The higher the score, the safer the
aircraft is and the less likely that
an accident will be fatal.
Metal aircraft with low stall
speeds and good stall/spin
characteristics, such as the
Pegazair and Zenair 701, get high
HAS scores.
Aircraft with high stall speeds
and poor stall/spin
characteristics, such as the
Lancair IV get low HAS scores.
2/16/14
Page 36
Crash Survivability Percentage
!
!
Taking the last twenty years of data from
NTSB accident reports and determining the
ratio of nonfatal accidents to total accidents
for a particular aircraft produces a Crash
Survivability Percentage.
The Crash Survivability Percentages for the
aircraft used as examples in the HAS score
are:
"
"
"
"
"
"
"
"
!
!
!
RV-7/7A -65%
Lancair IV - 49%
Sonex - 83%
Zenair 701 - 89%
Varieze - 73% s
Cessna 172 - 86%
Questair Venture - 61%
Pegazair - 100%
The Crash Survivability Percentage shows a
good correlation with the HAS score,
indicating some validity in the approach to
scoring. Once again, aircraft like the
Pegazair and the Zenair 701 have a high
survivability and aircraft like the Lancair IV
do not.
There are exceptions though, as can be seen
by the HAS score for the Sonex when
compared to the Crash Survivability
Percentage.
One variable not considered in this analysis
is the type of pilot a particular homebuilt
attracts, and the type of flying they do.
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