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below a level that would cause serious injucies to the occupant. A rigid
nonyielding or hard seat can lead to high peak loads on the occupant causing
serious injuries. A frangible seat, one in which the attachments or seat
parts break during impact, can lead to high peak impact forces on the
eccupants during secondary impacts with aircraft floors, panels or other
structures. Seat placement (over main spar, near the floor or on or near
other nonyielding structures) or seat failures of one degree or another
were judged to have intensified the injuries of occupants in at least 30
percent of the accidents reviewed.- Common findings were: failure of
latching pins te restrain seats from traveling forward on seat tracks;
detachment from seat tracks, usually by breaking cf either the track or the
track~attachment mechanism; and fracture of seat legs and pedestals. These
and other findings (6) in which seats and seating placement appeared to be
a factor raise the question of the crashworthiness suitability of seats in
general aviation aircraft. In view of current FAA reguiations prescribing
minimum seat strength based on static testing (2), the data and observations
in this report, along with other accident data, indicate that an area for
improvement in occupant survivebility is in providing seats that attenuate
impact force to levels that can be tolerated. Additional documentation of
seats as related to injuries in general aviation accidents is the subject of
an ongoing accident investigation protocol in the FAA.

Except for lap-held infants and children, lapbelts were used by all
occupants of the aircraft reviewed. Only a few lapbelt failures were
noted and chese primarily were due to failure at the attachment rather than
the webbing. These findings support the general impression that if the
aircraft impact is in any way survivable, the belt webbing rarely fails
unless it is severely weathered and frayed, as seen in some ae: 1 application
aircraft, or it is configured so that the force of impact causes the
fitting te cut the fabric. The weakest portion of the lapbelt system
appears to be its attachments to the floor or aircraft structures.

Aircraft occupants use the lapbelt restraint but, for the most part, do
not use the UTR. The value of restraining the upper torso cannot be over~
emphasized. For example, a seated passenger is restrained by a lapbelt and
his/her upper torso may weigh as much as 120 lb. In an accident, the
lapbelt holds the pelvis and acts as a fulcrum about which the upper torso
rotates under the force of deceleration. If the deceleration is low, 2 G's,
the upper torso will have an apparent weight of 240 lb, so that the occupant
can barely resist the forward thrust. At 10 G's, well within the surviva-
bility envelope, the apparent weight of the upper torso will be 1,200 1b
and it will swing forward with great velocity, possibly hitting the head on
the instrument panel and the chest against the control wheel. Based on the
velocity of the upper torso and head and the stopping distance, a force of
several hundred G’s may be exerted on the skuli or chest. This rationale
is supported by the finding that about 70 percent of general aviation
accident fatalities have fractures of the skull (7). Crushing of the chest
is common. These observations were made before UTR's were mandatory in
aircraft.

i2



REFERENCES
Snyder, Richard G.: Impact: Chapter 6 in Bioastronautics Data Book,
Second Edition, National Aeronautics and Space Administration, NASA
SP-3006, 1973.
Federal Aviation Regulations, Section 23.561.

DeHaven, H.: Accident Survival - Airplane and Passenger Automobile.
Cornell University Medical College, January 1952.

Pennybolser, A. L., J. W. Ross, Jr., and G. L. Wilson: A Summary

ef Crashworthiness Information for Small Airplanes. Federal Aviation
Administration Technical Report No. FS-70-592-12Ca, 1973.

Kirkham, W. R., J. M. Simpson, T. F. Wallace, and P. M. Grape:
Aircraft Crashworthiness Studies: Findings in Accidents Involving
An Aerial Application Aircraft. FAA %ffice of Aviation Medicine
Report No. 80-3, 1980.

Kirkham, W. R.: Improving the Crashworthiness of General Aviation
Aircraft by Crash Injury Investigations. FAA Office of Aviation
Medicine Report No. 81-10, 1981.

Mason, J. K., and W. J. Reals: Aerospace Pathology. College of
American Pathologists Foundation, Chicago, Illinois, U.S-.A., 1973.

Federal Aviation Regulations, Section 23.785-
Federal Aviation Regulations, Section 91.33.

Federal Aviation Regulations, Section 91.7.

US. GOVERNMENT PRINTING OFFICE: 1932 369-605/740 1-5

21



to provide details. Trained crash injury investiaators, who had personally
investigated a number of these accidents or participated in the program at
the time the accidents were investigated, reviewed all records ané extracted
data. In addition, these investigators, based on the information at hand,
were asked to make judgments as to whether seats, lapbelts, upper

torso restraints, or cabin structures were involved in producing or intensi-
fying injuries in occupants. From these data a number of tables were derived
in an attempt to answer certain questions pertaining to crashworthiness.

III. RESULTS.

The findings in the 47 accidents are shown in Table I (appended).
Accompanying the table is the legend to codes used for representing the
findings.

These 47 accidents involved 138 persons (including 2 lap-held children).
There were 47 pilots, 40 occupants of the copilot seat, and 49 additional
passengers (in seats other than the pilot and copilot seats). It was
estimated that the major impact force was forward in 40 accidents, forward
and left in 3, and forward and right in 1, both forward and vertical in 2
and only vertical in 1.

One aircraft crashed inverted and another cartwheeled. The remainder
crashed on a straight or turning (coded as forward-turning) heading. Forty-
two accidents were judged to be survivable and the remaining five only
partially survivable.

Survival of an aircraft accident depends to a great extent on providing
a crash-resistant container for the occupants; that is, an occupiable area
that will withstand crash forces without crushing, collapsing, or disintegrat-
ing. The accidents were judged on the basis of overall damage indices for
nonoccupiable and occupiable areas. This crash severity index has been used
at CAMI for a number of years. It is inadequate to describe fully what an
investigator may observe but serves as a means of estimating damage so that
accidents generally may be compared. Such a comparison is shown in Table II.

Damage, as assessed by this method, confirms what one would expect,
that the nonoccupiable structures of wings, tail, and engine, sustain greater
destructive damage than the more capsulized cabin. Indeed, the crumpling
and breaking away of these exterior structures, to some extent, cushions the
fuselage against the forces of the impact.

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Based on their familiarity with the accident or their experience as
erash-injury investigators, the reviewers correlated the injuries in each
accident with the apparent dynamic scenario of the crash. For each occupant
of each aircraft they then estimated whether or not, in their opinion, a UTR
would have been of value in reducing injuries in this selected series of
accidents. These estimates along with the occupiable area severity damage
are shown in Table VII.

Among these accidents there are rare examples ia which a UTR was used
and greatly aided in survivability of the occupant. Unfortunately, most of
the occupants of the aircraft did not have the advantage of having a UTR
available and, for the most part, those who had them available did not use
them. Among pilots, an estimated 43 woul@ have benefited from a UTR, versus
4 who would not have benefited. Among copilots 36 would have benefited as
compared with 4 who would not have benefited. Similarly, among passengers,
42 would have benefited as compared with 11 who would not have benefited. it
is apparent from these selected accidents and these estimates, that UTR's
would have reduced the severity of injuries to aircraft occupants in all
positions. These findings and experienced opinions are consistent with
other field investigative findings, laboratory dynamic studies, and FRA
requirement that general aviation aircraft nanufactured after July 1s, ly7s
have UTR's installed for each front seat.

Injuries to aircraft occupants by seat position are shown in Table VITI.
There were 17 fatalities, mostly in the pilot and copilot positicns. Those
injuries classified as serious with 10 percent or more residual disability,
such as the loss of an eye, an extremity, or the impaired ability to work,
all cccurred in persons in pilot and copilot positions.

The known types of serious injuries received are shown in Table Ix.
Pilots and copilots received roughly a third of their injuries to the head
and face, a third to the chest and a third to the spine. Spinal
appeared to predominate in passengers although about one-fourth of injuries
were to the head and face. A further look at spinal injuries comes from
Table X in which known spinal injuries and compression fractures of vertebrae
are tabulated. These figures show that the majority of serious spinal
injuries in aircraft accident victims is compression fractures.

Iv. DISCUSSION.

The data in this retrospective study, iike much accident data, were
not collected under a protocol that forced investigators to document specific
findings such as attachments of all seats or precise review of hospital
records on each occupant for exact details of injuries. Even so, the data
recorded, findings familiar to the investigator, and the photographs allow
a@ reasonably good overall evaluation of each accident.



Who receives the worst injuries when both pilot and copilot positions
are occupied? To explore this, the severity of injuries to the occupants
of the pilot position (left front) and occupants of the copilot position
(right front) was recorded. Of the 39 accidents, in which both positions
were occupied, injuries to occupants of the pilot and copilot positions were
greater in the pilot position in 10, greater in the copilot position in 10,
and equal in the remaining 19. Of course, injuries are probably a function
of which side of the aircraft impacts first. There were six fatalities at
the pilot position and seven at the copiiot position. These data suggest
there is no difference between these two positions in regard to the severity
of injuries received.

Is one likely to receive more serious injury when occupying the cockpit
(pilot or copilot position) or a position behind the cockpit? Table IV
presents data on 23 accidents in which there were occupants in passenger seats
as well as the cockpit. The most serious injury of an occupant in passenger
rows other than the first is included for completeness. The injuries listed
represent only the worst injury an occupant or occvpants received in their
position in the aircraft. There were three accidents that involved a fatal-
ity in the cockpit. Of these three accidents, the most severe injury to
other occupants in the aircraft was a “serious” injury. There were 16
accidents in which the most severe injury in the cockpit position was
"serious," yet, in three of these, there was at least one fatality in the
first row of passenger seats. There were four accidents in which injury
to an occupant in the cockpit was minor.none; occupants in the first passenger
row received "serious" in one accident and minor or no injuries in the
other three accidents. In two accidents, the most severe injuries
were in the second row of passenger seats. With some notable exceptions, such
as case #27 in which occupants of the pilot and copilot seats survived but
both occupants behind them received fatai injuries, these data tend to con-
firm the accumulated observational experiences of general aviation crash-injury
investigators that persons in the pilot and copilot positions are subjected
to greater impact forces and thus receive more severe injuries than occv-
pants in rearward positions in the aircraft. There appears to be a cabin
damage gradient in the occupiable areas, greater forward and diminishing rear-
ward, and similarly there appears to be an occupant injury gradient, greater
forward and diminishing rearward. he two are cbviously correlated.

TABLE Iv. Comparison of Injuries in Cockpit Area With Those
Received in Other Locations in Aircraft*

Passenger Passenger Passenger
Cockpit First Row Seconé Row Third Row
(Pilot-Copilot | MINOR | MINOR | MINOR
Positions) | SER NONE | FAT NoNE | FAT SER NONE
|
Fatal 3 | 2 1 | l
Serious 16 | 30 6 7 ' 1L 2 1
Minor/None 4 | 1 3 | 2
23 3 2 4k 3 3 i

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TABLE II. Damage Indices (See Table I)

Nonoccupiable Occupiable

Damage Index (#_ of Accidents) (#_of accidents)
Minor None 8
Moderate 13 is
Moderately Severe. 10 13
Severe 13 7
Extremely Severe 5 1
Extreme 5 3
Unclassified 1
Damage to: # of Accidents

Nonoccupiable Area > Occupiable Area 30

Nonoccupiable Area = Occupiable Area 14

Nonoccupiable Area < Occupiable Area 2

The results of a comparison between the damage to the cockpit area and
the remainder of the cabin in 29 of the accidents (where such comparizon was
meaningful) are presented in Table III. Damage to the cockpit area was
tabulated to be significantly greater in 13 of the accidents and equal in the
remaining 16. In no instance was damage to the remainder of the cabin greater
than to the cockpit area. In many individual accidents the differences in
fore and aft damage in the occupiable areas were extreme.

TABLE III. Cockpit/Cabin Integrity in Accidents

Cockpit Remainder of Cabin
(# of accidents) (# of accidents)

Intact 3 16
Distorted 5 6
Partly Collapsed 12 6
Collapsed 2 1
Burned ce) 0
Disintegrated 1 ie)
Structural Damage to: # of Accidents

Cockpit > Remainder of Cabin 13

Cockpit = Remainder of Cabin 16

Cockpit < Remainder of Cabin ie}

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TABLE VI. Contribution of Seats to Severity of Injury

Seat Did Not

Seat Contributed Contribute To
Seat Position To Severity injury Undetermined
Pilot 16 26 5
Copilot 21 26 3
Passengers 14 34 i
Total 41 86 9
Percent 30 63 7

In 30 percent of the accidents, malfunction of a seat component (some
factor in the seat), fracture of legs, separation from the seat~track, etc.,
contributed to injuries of occupants over and above what would have been
expected from iiy::t forces. In some accidents it was obvious that a
factor in the seat design was a contributor to injuries.

Almost all seats were forward-facing but there were, in these
aircraft, six aft-facing and three fixed side-facing seats that were
occupied. Two occupants of side-facing seats received only minor injuries,
{Case #25). In another (Case 437), the only occupant to receive greater
than minor injuries was in a side-facing seat. This occupant had serious
abdominal injuries related to seatbelt compression of internal organs.

The tubular frame of one of two aft-facing seats in Case #21 broke,
allowing the occupant to come forward and strike the pilot from pehind,
adding to the pilot's injuries, as he was more forcefully driven into
the instrument panel. Only minor injuries were incurred in two aft~facing
seats in Cases #25 and #37. Injuries occurred to occupants of aft-facing
seats in Case #47, but both seats were loosened by severe cabin and floor
damage and occupants in their seats were thrown out of the aircraft.

The standard method of restraining occupants in an aircraft is by means
of a lapbelt. In only two accidents were there well-docmented lapbelt
failures. In one (Case #10), the lapbelt attachment to the floor of the
aircraft failed, allowing the pilot to be huried out of the cabin and
receive fatal injuries. In Case *ll, a severe impact, both iapbelts
failed and the occupants were thrown free of the aircraft. Both occupants
survived.

An upper torso restraint (UTR) (or other adequate head protection
in accidents) has been mandated in some aircraft by the Federal Aviation
Regulations (8,9). In accidents reviewed, 57 occupyants had the availability
of a UTR. Of these, seven were used and held For six occupants the use
and function of a UTR was unknown. The remainder (44) did not use the
available UTR.

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TABLE VIII.

Injuries to Aircraft Occupants

Seat Serious With
Position Fatal Residual Serious Minor Unknon
Pilots 6 4 24 12 ie) L
Copilots 7 2 20 9 2 0
1A 1 8 5 2 a
1B 3 6 6 3
2A 3 2 i
2B 3 2 1
2c i i
3B
Totals 17 6 4 37 * 10 Zz
Percent 12.5 4.4 47.0 27.2 7.4 1.5
TABLE IX. Distribution of Major Injuries
Total # Eead and Face Chest Abdomen Spine
Position Tabulatec # & = % 2 % # &
Pilot 37 di 36 i2 32 L -- 13 35
Copilot 37 il 390 1c 27 3 8 13 42
Passengers 26 6 23 6 23 1 -- 13 45
TABLE X. Spinal Injuries
Spinal Injuries Compression Fractures
2 cia &
Pilot 13 i] 6¢
Copilot 13 5 38
Passengers 13 Lo 77

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Since the seat is an integral part of the aircraft occupant protection
system, how did the seats function in these accidents and did seat failures

or loss of adequate seat support add to the severity of the injuries received
in the accidents analyzed?

Aircraft were found to have varying degrees of failures of the seats.
Failures, to a great extent, varied with the design, installation, and
position in the aircraft. For example, seats were found to fail at the
attachment by sliding forward on the seat track, and to partially or com-
pletely detach from the track. Legs or seat pedestais were found to break,
or break and the broken parts separate. For the most part, bending of legs
and pedestals was considered beneficial to occupant protection. There were
some failures of seat pans and seat backs. The data covered 136 seats. Of
these, seat-to-track/floor attachments failed in 48, legs/pedestals failed
in 25, and backs in 6. The distribution of these failures is represented by
the data in Table v.

TABLE V. Incidence of Seat Failures

Seating Position Attachments Legs/Pedestals Back
Failures{ Total #| %{ Failures| Total #} %| Failures} Total #
Pilot 19 44 43 10 46 2. 2 44
Copilot 16 39 41 9 38 24 4 39
1A 4 16 25 2 16 13 ce) 15
1B 6 17 35 2 17 12) 0 16
2A 2 6 33 i 6 17 1 6
2B 1 6 17 1 6 17 1 6
3A ie) 1 ie} 1 ie} i
3B 9 1 | fa) 1 ia) 1
} :

Here again one can see a gradient of failure from forward toe aft. From
these data and the general experience of investigators, the greatest failures
are in the pilot and copilot seats with the seat to track/floor attachments
failing in approximately 40 percent of the accidents. In 20-25 percent of the
accidents there was some breaking of the seat leg or pedestal. Other seats
appeared to fare better but still there were enough failures to warrant concern.

For improved crashworthiness, seats should provide support for the
occupants and attenuate both forward and vertical impact forces. Abrupt
failure such as sliding forward, separating from the attachment to the floor
ef the aircraft, or breaking of the undersupport (iegs/pedestals) aliows
occupants to impact against the floor, instrument panels, and other occupants
er structures so that the decelerative forces are greater and injuries are
incurred. Similarly, in some respects, a seat that is rigid and unyielding
may intensify injuries. There are no FAA requirements for seats to attenuate
decelerative forces. The accidents wer: reviewec with the question in mind
that, from practical considerations, did the seats contribute to the severity
of the injuries? Such data are tabulated in Table VI.



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It is also helpfu- to analvze accidents to estimate the severity of the crash,
noting the integrity of the structure, analyzing the performance of the
reStraint systems, and reviewing injuries received by occupants. Findings in
accidents can be confirmed under controlled conditions in the laboratory.

For over a decade an ongoing biomedical and crash injury field investi-
gation resear program has been conducted at the FAA Civil Aeremedical
nstitute (CAMI). In this program, accidents were investigated to reveal
any of a wide range of human factors such as: previous illnesses in the crew;
medications or drugs taken by the crew; fatigue; physical stresses; psycholog-
ical stresses; types of injuries received; causes of impact injuries; emergency
egress from aircraft; smoke and fire as related to survivability; other en-
vironmental conditions such as water, ice, and snow, as related to postcrash
survival; and a number of other biomedical factors that may have contributed
to the crash or related to occupant injury or survival. Pindings as related
to survival of the impact have been a prominent feature of these investiga-
tions. Although each investigation was not undertaken specifically to
investigate crashworthiness, certain such aspects came forth in many investi-

gations. cse included features such as the deformation of aircraft cockpit
andi cabin structures; the state of integrity and probable function of seats
and ‘tt systems; probable impact of occupants against aircraft struc-

tures and correlation of injuries with the direction and severity of
impacts. The func: ion and adequacy of seats and restraints have been of
particular concern (5) because modifications of these systems, to give greater
protection to occupants, often can be made at less expense to manufacturers
or aircraft owners, than modification of the airframe. Indeed, some specific
changes made by manufacturers, as a result of these investigative activities

proved the crashworthiness of the respective aircraft and have

(6), nave i
savecé lives.

, we have surveyed a number of general aviation accidents
ent of findings, particularly as they relate to the
aint system-~seats, lapbelts, and shoulder harnesses.
Elements ofthese data have been used in other reports (6).

TODS .

personnel from 1973 to and including most of 1979.
nts investigated from CAMI prior to 1973 were previously reviewed (4).
of accidents was reviewed for a number of features of crash-
iness and, n particuiar, for the injuries to the occupants in relation
to apparent severity of the impact and the adequacy of the function of the
cabin and restraint systems. All aerial application aircraft accidents,
acc nts i ich all occupants were killed, or where fire or water precluded
a reasonable evaluation, were climinated from the series. In all, 47 of a
greater number of accidents were deemed worthy of more intensive review and
tabulation, in that there was meaningful information in the accident reports
or investigators were familiar enough with the particulars of the accidents



Thus, for years it has been known that UTR's would be lifesaving to
aircraft occupants in accidents. The double shoulder harness worn by
aerial application pilots has saved hundreds of lives. Unfortunately
there are few findings of other general aviation aircraft occupants wearing
a UTR at time of impact. Of the 57 occupants of aircraft in this report
who had a UTR available, only 7? used them and the UTR appeared to have
lessened injuries. An outstanding example of the value of a UTR is Case #33
where the occupant in the copilot seat, an FAA employee, was estimated to
have survived only because he had on the single shoulder harness.

Estimates based on accident investigation experience, as reflected in
Table VII, show that of the 136 persons evaluated in the 47 accidents, 121
persons would have benefited by a UTR; the remainder would not have benefited.

Tne FAA has taken steps which should lead to improved occupant
protection in survivable aircraft accidents. The Federal Aviation Regule-
tions (FAR) have been changed so that since July 18, 1977, all new type-
certificated airplanes must be equipped with UTR's in the front seats. For
a pilot to operate a small civil airplane manufactured after July 18, 1978,
the airplane must have, for each front seat, a shoulder harness designed
to protect the occupant from serious head injury when the occupant experiences
the ultimate inertia forces specified in other parts of the FAR (9). In
addition, the FAR mandate that UTR'’s be worn on all takeoffs and landings
by each required flight crewmember of a civil airplane, the airplane is
equipped with a shoulder harness and if the shoulder harness does not
interfere with performance of duties (10). There is no provision that,
in new type-certificated or newly manufactured aircraft, other seating
positions (except for additional crew positions) be equipped with a means
of restraining the upper torso. Neither is there provision that aircraft
manufactured before the stated date be retrofitted with UTR's in any
position. Crash injury experiences in other vehicles, decelerative testing
under laboratory conditions, general aviation accident experience, and the
experience and data in this report, all indicate that general aviation
aircraft occupants under conditicn of impact, would benefit from wearing
a UTR. The FAA's requirement of a UTR in certain airplanes and other
crashworthiness improvements such as removal of sharp objects, installation
padding, etc., should reduce injuries and improve survivability.

The figures in Table IX indicate that in reughly a third of the
occupants, severe injuries are to the head and face, a third to the chest,
and a third to the spine. For the most part, in accidents where the
cockpit/cabin retains its integrity and is not crushed upon its occupants,
the severe head and face injuries probably result from the unrestrained
torso traveling forward against aircraft structures. For the pilot and
copilot positions this is most frequently the instrument panel or structural
members. For other occupants, head and face injuries, usually less
severe than for pilot and copilot positions, are receivedé as they flex
forward into the seats in front of them or move laterally into aircraft
structures. Chest injuries in the pilot and copilot position frequently

13


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CRASHWORTHINESS STUDIES: CABIN, SEAT, RESTRAINT, AND INJURY FINDINGS IN
SFLECTED GENERAL AVIATION ACCIDENTS

I. INTRODUCTION.

The prime goal of aviation safety is to prevent injuries, loss of life,
and loss of property. Of course, this is best done by keeping ac lents from
happening; the greatest efforts rightfully should be and are directed toward
prevention.

However, accidents do happen and, based on past experience, they do occur
with a certain predictability. Indeed, data gathered by the National Trans-
portation Safety Board for a recent 6-year period (1973 through 1978) record
a yearly average of 3,911 "small fixed-wing aircraft" (under 12,500 1b) in
accidents. Of these, 663 (or 16.7 percent) resulted in one or more occupants
being killed, with 1,303 being killed, as an average, or, statistically, two
persons per fatal accidert. In addition, there was untold injury, pain,
suffering, and permanent disability in persons who survived the 663 (yearly
average) fatal accidents or who were occupants in the 3,248 (yearly average)
aircraft in nonfatal accidents.

Studies have shown that the human can withstand rather large impacts if
the forces are properly distributed to the body. Such tolerances to deceler-
ative forces have been amply demonstrated by a number of controlled studies
using human subjects (1) and by findings in vehicular and other accidents.

The tolerances, (withstanding decelerative forces without incurring permanent
debilitation) are derived from evaluating impacts in relation to dynamic
considerations such as rate of onset and duration of deceierative force acting
upon the body. Besides varying with the rate of onset and duration, human
tolerances are variable with other factors such as height, weight, and age of
the individual; the type of restraint used; the application of the restraint
to the body; etc. The crashworthiness load requirements applicable to seats
and restraint systems specified in the Federal Aviation Regulations (2) are
based on ultimate aircraft airworthiness load requirements met under static
loading conditions. Although human tolerances to short duration dynamic loac-
ing appear to exceed several-fold the static loads applicable to seats and

t systems, @ mic and static loading are not directly comparable.
ation of meaningful impact attenuating standards for seats and

ire definition of the dynamic components of crashes.

aints will re

One of the greatest challenges to aviation safety in the coming years
will be to make aircraft more crashworthy, i.e¢., to build and equip aircraft
so that when a crash occurs the aircraft itself provides greater opportunity
(within practical limitations} for reduced injury to occupants. Many of the
developments in crashworthiness research are aimed at better cushioning of
occupants against the decelerative forces of the crash. The most fruitful
and practical means of doing this is by applying previously advocated packaging
principles (3), and especially by improving seats and restraint systems (4).

aa NERC TNS.



Sonam .

Technicol Report Decumentction Page

f
1

T. Report No. ZT Government Accession No. 3. Recipient's Cotalog No.

FAA-AM-82-7 AD - AW4Y ng

4. Title and Subtitle
CRASHWORTHINESS STUDIES: CABIN, SEAT, RESTRAINT, AND MARCH 1982

5. Report Dete

INJURY FINDINGS IN SELECTED GENERAL AVIATION ACCIDENTS] &. Performing Organization Code

18. Performing Orgomzation Report No.

7 Author's’

William R. Kirkham, S. Marlene Wicks, and
Donald Lee Lowrey

9. Performing Organ: zation Nome and Address. 10. Work Unit Ne. (TRAIS)
FAA Civil Aeromedical Institute |
P.O. Box 25082 1}. Contract or Grant No.

Oklahoma City, Oklahoma 73125

13. Type of Report and Period Covered

12. Sponsoring Agency Nome and Address
Office of Aviation Medicine
Federal Aviation Administration

800 Independence Avenue, S.W. 14. Sponsoring Agency Code
Washington, D.C. 20591

15. Supplementary Notes

This work was performed under Task AM-B-81-TOX-23.

6 Abstract

This report reviews 47 survivable or partly survivable accidents investigated since
1973 by personnel from the Civil Aeromedical Institute. The accidents were reviewed
for a number of features of crashworthiness and, in particular, for injuries to occu
pants in relation to the severity of the impact and the performance of cabin and
restraint systems. Opinions were rendered by trained crash injury investigators as
to the role or expected role in seats and upper torso restraints in adding to or
lessening the injuries.

The Gata support the general concepts that nonoccupiable portions of the aircraft
receive greater physical damage than occupiable areas. The greatest damage to the
occupiable area is to the forward portion of cockpit/cabin and the occupants have a
greater chance of survival if the cockpit/cabin remains reasonably intact. Occu-
pants seated forward in the cockpit/cabin receive greater injuries than those seated
more rearward. Further, the findings suggest that seat placement or seat failure
to one degree or another intensified injuries (as compared to more optimum crash-
worthy seats) to occupants in at least 30 percent of the accidents reviewed. Upper
torso restraints, in the few instances used, were beneficial, and had they been used
by all occupants, would have significantly reduced the injuries.

The report discusses the relation of the occupant to the seat and restraint system
and the apparent benefit to be derived from a well-designed impact attenuating seat
and, in particular, use of an upper torso restraint.

i i
[I7. Key Words TS. Distribution Storement
_. Decument is available to the public
Accidents . through the National Technical Information
Crashwor-hiness Service, Springfield, Virginia 22161
Injuries

Survivability

] 19. Secunty Clossif. fof this report) 20. Security Clossif, (of this pose) { 21. No. of Pages | 22. Price
i

| s£4

i Unclassified Unciassified 21

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized



The accidents reviewed here confirm what is apparent to aircraft
accident investigators, that:

1. The nonoccupiable portions of the aircraft receive greater physical
damage than the occupiable areas.

2. I£ occupants are to survive the accident, tne cockpit/ceabin shoula
remain reasonably intact and not collapse upon the occupants.

3. The greatest damage to the occupiable area is to the forward
portion of the cockpit/cabin.

4. Impact forces on the aircraft, Sor the most part, cause greater
injuries to occupants seated in the forward position of the cockpit/cabin
than those s-ated more rearward.

What is not always apparent to general aviation accident investiyators
is that, in specific accidents, injuries and even overali survivability
of the impact may be related to a lack of incorporation of crashworthiness
features of the aircraft. Investigators intent on determining the cause
of the accident may overlook the fact that occupants may have survived
the accident had some feature not been present, had a seat not failed, or
had a shoulder restraint been used. Also, they may not take cognizance
of the fact that a properly restrained occupant in some crashes may
withstand impact forces that would severely damage the integrity of the
aircraft. Each of the accidents reviewed was survivable or partly
survivable fzom the standpoint of what a welli-restrained occupant can
withstand.

BR basic principle of occupant survivability is that the container
(the cockpit/cabin) remain intact end not crush in upon the occupants.
Experience reveals that in most accidents the forward portion of the
aircraft, the landin¢e gear and the underside receive the brunt of the
impact forces. Generally, crushing is from forward to aft in such a wey
that the pilot and copilot are subjected to more longitudinal force than
occupants seated behind them. There appears to be no difference of injury
potential between the pilot and the copilot positinns. Passengers have
the advantages of more bending, crushing, and deformation of aircraft
structures forwaré of them so that they are spared the full impact forces
experienced in the pilot and copilot positions. This is brought out even
in this limited data.

To withstand
The seat is an ir

pact forces, occupants showld be adecuately restrained.
tegral part of any restraint system and the optimum

forces, which ere greatest in almost all accidents. ideally,
a seat should initially resist impact forces and then bend and deform a
controlleé and progressive manner so es to attenuate and keep forces

id



result from impact with the control wheel or by forward flexure onto one's
own legs. Seats that travel forward, or that partially or fully detach, add
to head and chest injuries. Crushed chests are less frequent in passenger
positions, but can result from flexing forward and striking one's own knees.
Both types of injuries would appear to be lessened by restraining the

upper torso.

Spinai injuries are usually attributed to severe downloading. Overly
rigid seats, seats that break and let the occupant "bottom out" on the floor,
or seats that are positioned over solid structures or other unyielding
structures, add to the severity of spinal injuries. Compression fractures
of lower thoracic or lumbar vertebrae were conspicuous in the accidents
reviewed.

This type of injury probably results from downloading on the spine or
forward flexion over the lapbelt. The seat and restraint as an integrated
system is apparent when one considers how a UTR may work. Restraint of
forward motion and maintenance of the body in an upright position by the
UTR in many instances will increase downloading on the spine--and on the seat.
Increased loading on the spine should intensify injuries. It is chus
apparent that the seat should be designed to attenuate this increased
downloading so as to lessen injuries. The value of a seat that can attenuate
these and other forces on the occupants cannot be overemphasized. The
specifics of spinal injuries and seat failures should be given special
emphasis in aircraft accident investigations as UTR's become more widely
used. The overall and specific functioning of UTR's in general aviation
accidents is the subject of an accident investigation protocol within the
PAA.

The data from the 47 accidents in this report suggest that, although
variable with the specific airplane, the greatest crash protection for the
eccupants of general aviation aircraft can be offered by providing each with
a UTR (with strong attachments) and a well-anchored impact attenuating seat.
This can only be accomplished though at a significant cost for newly manu-
factured airplanes and a major cost as a retrofit item.

14