The accidents in which the seat was interpreted to have
influenced the injury are summarized as follcws:

Case 1: A Mitsubishi MU-2 crashed while the pilot

attempted an emergency landing during a thunderstorm near
Scottsdale, Arizona. Six of the occupants of this plane suffered
increased injury severity due to seat failure.
The pilot's seat detached from the floor and the pilot was
ejected from the plane. A female passenger, in an aft~facing
seat on the right side of the plane, sustained an injury which
almost amputated 2/3 of her thigh. In this case the seat failed
to protect the occupant from an object which protruded through
the cabin wall. Two other passengers also seated in aft facing
seats were killed when hit by flying objects. The seat failed to
protect these occupants from unrestrained cargo when the cargo
net attachments failed. Two other passengers in forward facing
seats were hit by flying objects and their seats alse detached
from the floor as heavy cargo moved forward at impact.

Case 2: A Cessna 172 crashed during takeoff seriously
injuring all four occupants. Two young men seated in the back
suffered severe facial fractures when the seat legs detached from
the floor and both lap belts failed, allowing both back seat
passengers to impact the back of the front seats.

Case 3: A Bellanca Citabria crashed while practicing
aerobatics. One of the back seat legs separated causing the five
point harness to fail. The pilot sustained fatal skull fractures
when his head impacted the instrument panel and windscreen.

case 4. The pilot of a Cessna 182 attempted to make an
emergency landing in a muddy field. The plane struck a slightly
elevated gravel road, detached the nose gear and slid 80-100 feet
in a 30 to 40 degree nose down attitude. The pilot's seat
partially detached and the copilot's seat completely detached.
The AME investigator reported that the seats effectively
attenuated energy to protect the occupants. Both occupants were
seriously injured with facial fractures.

case 5. The engine of a Cessna 172 failed during an
approach to the airport and an emergency landing in a field was
attempted. All four seats detached during the crash. The AME
reported the seats did attenuate energy and helped protect the
occupants from more serious injury.

Case 6. The engine ofa Beech Sundowner failed during a
touch and go landing. The pilot attempted to make a right turn
back to the airport, stalled and decelerated through several
trees. The pilot's seat remained attached to the floor, but the
legs of the seat deformed to cushion the impact.


10. Make comments regarding specifics of injuries, causes of injuries and especiaily rote of seats and/or restraints in causing
or preventing injuries. :

14. Comment on any other crashworthiness (injury causing) findings in this accident. Hlustrate any findings with sketches.

12. Record the manufacturer of seats and/or restraint systems that may have matfuncticned or failed.

13. Information coliected by:

Address -

Phone

FAA Form 8025-3 (1-81) Page 8


7. Seat Findings.

Complete this table Enter findings using codes given below. Record findings for each seat whether or not it was occupied.

‘Seat 5 Direction of | Vertical Fro | Seatto track | Seot iegs/
Position | Oeupied | Facing | Honiz, Forces | Forces Floor | Floor Attach, | Pedestai | Se#t beck | Pan/trome
a b a d e f @ h i i

FAA Form 8025-3

Codes for seat and restraint system findings.

a Seat Position. record position as designated in number 6,
cabin seating

». Occupied Yes NO

©. Facing.
A forward D - Fixed complete side facing
Batt € — bench side facing
C = swivel F ~ other (write in)

@ Directions of horizonts: (for.ard-aft lateral) forces acting
of each seat.

A left © — night
B - leftand forward —-F ~ right and aft
C- forward G— aft

D - night and forward H ~ left and aft

2 Vertical forces:

Downward Upward
A — minor D — minor
B - moderate E — moderate
C — severe F — severe
Floor:

A. No distortion or buckling under seat

8. Minor distortion or bucking under seat — enough to
cause only minor strain of seat track and/or attachment

C. Moderate distortion or buckling under seat ~- sufficient
to cause moderate strain but not fail seat tracks and/or
attachments.

©. Severe distortion or buckling under seats — enough to
fail seat tracks and/or attachment.

Z- Unknown

(sit

Seat-to-track/fioor attachment

A ~ seat remained attached to track/floor

6 — seat partially detached from track/fioor

C — seat completely separated from track/floor
D — not appheable Z — unknown

Seat legs and/or pedestal:

A — no seat deformation

8 — minor bending or deformation of seat leg and/or
Pedes:al

C — severe deformation or bending but seat legs and/or
pedestal not broken

D ~ legs and/or pedestal broken but not separated

E — legs and/or pedestal broken in several places and
badly separated

F — not applicable
Seat back

A — seat back damage minor or none

B ~ back broken but not separated

C — back broken and separated from seat pan
D — not applicable Z — unknown

Z — unknown

Pan/frame damage:

A —munor — sight bending or defermation

B -- moderate — pan/trame bent or warped but not
broken

C — severe or separated — bent and warped with fracture
of structural members

OD — not applicable Z— unknown

Page 4


Investigators were asked to estimate the directions of tre
forces that caused seat occupants to move during the accident
sequence. They drew arrows representing the movements cf seat
occupants with respect to the primary axes of the airplane.
While there was no attempt to impose a unit of measure for these
forces, the lengths of the arrows were proportional to the
estimated relative magnitudes interpreted by the investigator.
The angular relationships and the temporal sequence of the forces
represented by these arrows were also determined by the field
investigators. Quantitative measurements of deceleration
magnitudes, slope of the terrain, and the attitude of the
airplane at each impact point were generally not avaiiable.

Figure 3 presents the outiines on which investigators
inserted arrows to represent the seat occupants' motions during
the accident sequence.

FIGURE 3 - Drawings Sub: itted by Investigators


DISCUSSION

The data available for analysis in this study is
characterized by the usual limitations attendant to airplane
accidents that are investigated under various conditions of
opportunity and with varying degrees of thoroughness and
completeness. Many of the observations are merely best estimates
rather than precise measurements. While certain limitations may
have been introduced by the variety of observers, there was the
opportunity for individual bias to be limited by the many
independent inputs. We believe the main trends are credible even
though it may not be realistic to interpret ail numerical data
points with the precision and confidence expected in laboratory
conditions.

The idealized data base would logically consist of the
complete accident report along with photographs, the FAA form
8025-2 which includes the regional flight surgeon's review, a
complete autopsy examination with pathogenetic explanations of
all injuries and the FAA form 8025-3 designed for this study to
elicit critical relevant observations. This ideal was seldom
realized. Table I presents the sources of material submitted in
this series. Because all cases admitted to this series were
accompanied by FAA form 8025-3 which sampled critical areas from
all the other sources, essentiai data points were more
consistently available than Table I might suggest. The majority
of the observations were provided by aviation medical examiners
who were typically very highly motivated practitioners of
medicine with special interests and accomplishments in aviation.
The remainder of the cases were reported by FAA accident
investigators.

Under the best of circumstances, medical evidence derived
from accident investigation is difficult to obtain for a number
of reasons. When an accident occurs, it is a common practice to
remove the occupants from the wreckage and to seek medical
attention for survivors. When a trained Aviation Medical
Examiner is available in the area, it is often several hours to a
few days before he arrives at the accident site. Once the
occupants have been removed and the aircraft stored in a hangar,
it is extremely difficult to reconstruct relationships between
airframe structures and specific injuries. Often restraints have
been cut to remove cccupants and seats scmetimes are removed
entirely from the wreckage by rescue personnel. When an Aviation
Medical Examiner is not assignea to an accident, the medical data
collected is often scant and generally not suitable for research
regarding crash injuries.



Acknowledgement

The authors wish to acknowledge the efforts of the late
Dr. William Kirkham in initiating this project. The Aviation
Medical Examiners (AMES) who participated in the on-site
investigations and supplied data for the study are also
gratefully acknowledged.


4. Record NON-OCCUPIABLE area damage. Record by entering check in appropriate piace.

Aircraft
Structure Nose

Tait

Ring

LiWing

intact

Distorted/
Wrinkled

Bent/Partly
Collapsed

Buckled!
Crumpled

Broken!
Collapsed

Torn free/
Disintegrated

Use the following criteria:
Intact — No apparent damage

Distorted/Wrinkled — Demege 1s confined to slight bending, wrinkling or
twisting; however the structure retains its size and shape.

Bent/Partty Collapsed — Members are bent. twisted or deformed so thet
the structure as 3 whole has changed in general shape and decreased in
volume.

Buckled/Crumpled — Structures ara grossly bent or warped; show crush-
ing oF large creeses and wrinkles.

Broken/Ceilapeed — Structures are broken, broken down, caved in or
folded together.

Torn Free/Disintegreted — Mayor parts are separated, structural form is
Jost, structures are strewn about or broken into smaller parts.

5. On the following diagrams draw an arrow or arrows to record the direction or directions occupants
were thrown( in relation to the aircraft) at the time of impact / impacts. Use the length of arrow to
designate the relative force and numbers 1, 2, 3, etc., on arrows to indicate the sequence.

FAA Form 8023-3 u-01)

Pege 2


Table V ie a tabulation of injuriss reported on FAA form
8025-3 in order to determine their relative frequencies by
anatomic bedy region. The percentage of the population exposed
to the acoident experience who sustained injury to each of the
major body arees listed in the table are presented. Seven'percent
of occupants, although exposed to crash forces, were not injured.
Phirty six percent of occupants were Fatally injured, thirty six
percent seriously injured and twenty one percent sustained minor

UTY.

TABLE V DISTRIBUTION OF ALL INJURIES REPORTED
ON FAA FORM 8025~3

INJURY BY OBSERVED : FREQUENCY

BODY REGION FREQUENCY PERCENT
ALL HEAD INJURY 90 6g (90/133)
SEVERE HEAD INJURY 33 25 33/133)
CHEST INJURY 52 39 (82/133)
ABDOMINAL INJURY 38 29° (38/133)
PELVIC INJURY 9 7 (933)
SPINAL INJURY 29 22 (29/133)
LOWER. 2
OR ENITIES 39 9 (39/133)
UPPER 30 23 (30/133)
EXTREMITIES :

This table presents the number and percent of the 133 total
occupants exposed to injury producing forces to each body region.

16



The likely mechanism explaining this disparate relationship
involves the occupant in "survivable" accidents selected by this
series experiencing inertial forces which tended to separate him
from the seat resulting in not loading the seat and in preventing
contact with the seat. It would thereby tend to lose its
opportunity to serve as an impactor. In such circumstances, the
seat would appear to be successful merely by remaining attachec
to the airframe without having to sustain the added forces
introduced by the occupant's mass. If the population in this
series were weighted toward those occurrences in which there were
predominantly vertical loads applied to the seat and its
occupant, the results may have been different. The available
data would indicate that the seats’ influence on injury severity
is relatively small. It is likely that the injuries caused by
factcrs other than the seats would overshadow findings of seat
induced injury.

The related issue of high versus low energy impact was
subject to examinaticn by using the vectors described as being
less than 15 degrees to identify low energy events in comparison
to those cases in which the resultant vectors exceeded i5
degrees. NTSB findings in (20,21,22) suggest that this technique
can assist in identifying the high energy impacts. Table III
presents this tabulation to show the expected increase in injury
with high angle events. A corresponding increase in seat failure
suggests that injury and seat failure may both be dependent or
another variable, very probably the magnitude of the energy
transfer and the associated large accelerations. The question of
causal relationships between seats and occupants’ injuries is
directly addressed by responses presented in Table Iv. In 10% of
the cases the seat was considered to have added to the injury; in
8% the seat attenuated or diminished the injury while in 82% the
seat appeared to play no role in inflicting the cbserved
injuries. This finding agrees with Cannon's (2) study which
points out the difficulty of establishing a causal relationship
between a particular structural failure and coincident injury.

An analysis of the injuries sustained by seat occupants was
attempted in an effort to examine whether or not the nature of
the injuries might help define the role of the airplane seat in
causing or attenuating those injuries. Unfortunately, in the
vast majority of the injuries reported, the precise pathogenetic
mechanism for the injury was never established. Consequently,
injuries to the spine and pelvis described by the existing data
from this series could have developed from a variety of
mechanisms that could not be differentiated.

21



Table VII represents the distribution of impactors for the
78 occupants who had a response for this question (58% of the
total population). Seventeen occupants struck no objects and the
impactor was unknown for 38 occupants. There were 147 impactors
reported for this group. The intrument panel and the yoke were
most often reported as impactors which would indicate a
predominantly forward motion of the occupant.

TABLE Vil

DISTRIBUTION OF INJURY PRODUCING
IMPACTORS
IMPE STOR | FREQUENCY | PERCENT
YOKE 31 at
INSTRUMENT PANEL 38 24
STRUCK BACK OF SEAT 12 8
STRUCK BY 1 7
FLYING OBJECT
MADE IMPACT a 3
WITH FLOOR
MADE IMPACT WITH " 7
RUDDER PEDALS
MADE IMPACT WITH 10 7
WINDSCREEN/WINDOW
STRUCK COCKPIT/CABIN 24 46
STRUCTURAL MEMBERS
STRUCK OTHER OBJECTS 8 5

18


6. Cabin Seating
Code seat locations in accident aircraft at bottom of page using alpha/numeric codes 2s shown in examples below.

EXAMPLES
Large Aircraft Small Aircraft
Nose of Aircratt Nose of Aircraft
PP cp
PP cP
NV FE
oe 1A 1B } Row1
Row1}1A,15,1C 10, 16, 1F PR — Pilot 2a 2B | Row 2
Row 2|2A,28,2C 2D, 2E, 2F oh — oriiet
Row 3|3A,38,3C 30, 3E, 3F — Navigator
ete. | ete. FE — Flight Engineer ete. | ete.
OB — Observer
1& — Row 1, Seat A
2B — Row 2, Seat 8
3C — Row 3, Seat C
Accident Aireraft
Nose of Aircraft
Please record all seats and
use these seating designations
in completing the table in
Question #7 & #8.
Comments:
Row 1
Row 2
Row 3
Row 4

FAA Form 8025-3 (1-81)


TABLE ilt
RESULTANT FORCE DIRECTION AND CONSEQUENCES

RESULTANT VECTOR SEAT & OCCUPANT OUTCOME
<15 DEGREES 11 ACCIDENTS (26 OCCUPANTS)
12% SEAT FAILURE (3/26 SEATS)

58% SERIOUS/FATAL INJURY (15/26 OCCUPANTS)

>15 DEGREES 9 ACCIDENTS (48 OCCUPANTS)
17% SEAT FAILURE (3/18 SEATS)
83% SERIOUS FATAL INJURY (35/18 OCCUPANTS)

As the terminal flight path became steeper or more nearly
vertical, there was a tendency for greater seat damage and injury
to be inflicted. This relationship is represented in Table III.
Neither the proportion of seat failures nor the proportion of
serious/fatal injuries are significantly different statistically
at low impact angles vs. high impact angles. Using the chi
squared test, p=.63 and .07 respectively. This is likely due to
the small sample size, sample selection and imprecise
measurements. These results parallel those of the NTSB reports
which define opportunity for survival as a function of impact
angle and airspeed.

The frequency of seat failure among persons with serious or
fatal injury was considered. Out of a group of 96 occupants who
were seriously or fatally injured, 46 were in seats which failed.
The binomial test yields a p value of 0.69. This p value
indicates that there is no statistically significant difference
in the observed proportion of seriously/fatally injured persons
in tailed seats from those in seats that did not fail (26).

Without controlling for energy level, it is not appropriate
to infer a causal relationship between seat failure and injury
severity. Energy level is related to both seat failure and
injury severity so that any apparent association is likely due to
the energy level exerted on both the seat and the occupant. It is
not proof of a causal association between seat failure and injury
severity.


Several cases were investigated by crash injury
investigators from the Civil Aeromedical Institute (CAMI). The
relevant information derived from these efforts was submitted to
FAA regional flight surgeons who reviewed the documents,
commented and interpreted them as they saw fit and forwarded them
to the Civil Aeromedical Institute, CAMI, for collation and
analysis.

To facilitate the acquisition of the appropriate evidence
and to introduce a degree of uniformity into the data acquisition
process, CAMI developed a form (FAA form 8025-3) on which
critical observations were recorded and data automatically
processed. This form called for estimates of the attitude of the
airplane at impact, damage to occupiable and non-occupiable
portions of the airframe, diagrams of the directions the
occupants were thrown at impact, force directions and damage
affecting the seats, restraint system characteristics, the
injuries inflicted on the cccupants and the causes of injury.
(see Appendix A) There were two questions inviting narrative
comments regarding injury pathogenesis and crashworthiness.

Sources of information collected for analysis included:

1. The National Transportation Safety Board report
of the accident (NTSB Form # 6120.4)
2. The Report of Medical Findings in Aircraft
Accidents, FAA form 8025-2
3. The Special Study Form, FAA form 8025-3
4. Photographs of the accident site and the
injuries sustained
5. Autopsy protocols
6. Comments and interpretations by the regional flight
surgeon.
Many observers did not respond to all questions and there is some
suggestion that the questions were not always interpreted in the
same way. The occasional responses that included mutually
exclusive descriptions were either corrected or deleted. All of
the desired information was available only in rare instances.
However, since the FAA form 8025-3 included a synthesis of the
critical information that would ordinarily be distributed through
all the sources described above, a case was accepted into this
series if the FAA form 8025-3 was available and case selection
criteria were met.

In order to assess seat failure it was necessary to define
consistent criteria which could be applied to the whole series,
since individual observers were not provided uniform standards by
which to establish failure. Frequently, no assessment of the
significance of a given seat damage was provided.


APPENDIX A

FAA Form 8025-3 (1-81)


10.

11.

REFERENCES

Brinkley JW, Raddin JH, Biodynamics: Transitory Acceleration.
In: Fundamentals of Aerospace Medicine Roy DeHart Ed. Lea &

Febiger, Philadelphia. 1985 p. 184-186, 199.

Canncn MR, Final Program Report for the Controlled Impact

Demonstration Seat Experiments and Development, Test Results,

and Cost Benefit Study. Simula 1985.

Chandler RF, Human Injury Criteria Relative to Civil
Aircraft Seat and Restraint Systems, Aerospace Technology

Conference and Exposition, Long Beach, Calif Oct 14-17,
1985.

Chandler RF, Data for the Development of Criteria for
General Aviation Seat and Restraint System Performance.

General Aviation Aircraft Meeting and Exposition, Wichita,
KS, April 16-19, 1985.

Coltman JW, Design and Test Criteria for Increased Energy
Absorbing Seat Effectiveness. Simula, 1983 FAA-AM-83-3.

Desjardins SP, Simula Inc., Aircraft Crash Survival Design
Guide; (Volume IV) Structural Crashworthiness USARTL-TR-79-

22 (A-E); 1980; Applied Technology Laboratory, U.S. Army
Research and Technology Laboratories (AVRADCOM), Fort Eustis,
Virginia 23604.

FAA Advisory Circular AC-No.21-22; Injury Criteria for Human
Exposure to Impact. 6/20/85

FAA Statistical Handbook of Aviation- Calender Year 1983. US
Dept. of Transportation, FAA p. 170.

General Aviation Safety Panel (GASP) Propos. or Enhanced

Crash Tolerance for Small (FAR Part 23) General Aviation
Aircraft with Fewer than 10 Passenger Seats. Federal

Register 1-31-83 CE-83-1 #23494,

Gikas PW, Forensic Aspects of the Highway Crash Pathology

Annual 1983: 18 pp 147-163.

Greer DL, Breeden JS, Heid TL, Crashworthy Design Principles,
General Dynamics/Convair Contract # FA-WA-4583 Sept 1984.

FAA-ADS-24.

24


However, the rearward-facing seat has found limited applicaticn
in general aviation. Sideward facing seats introduced
characteristic problems. Aircraft design engineers have
demonstrated the potentially beneficial influence that aircraft
seats can introduce into those events characterized by prominent
vertical accelerations applied approximately parallel to the
eccupant's spinal column, Gz (6,24,32,33). Seats can provide
needed additional stopping distance and can help change the rate
at which energy is released to the seat occupant and help reduce
potentially damaging energy transfers to noninjurious levels
(12). It is not clear which of these diverse experiences with
vehicular seats are similar to seat performance in actual light
airplane accidents and how much influence seat design has on
injury occurrence and severity.

Research into automobile accident experience indicates that
the seat typically had little to do with determining occupant
survival (16). The accelerations commonly applied, -Gx, tend to
separate the victim from his seat through the action of inertial
forces which cause the occupant to travel toward the front of the
vehicle (9,10). The seat in such events, characterized
predominantly by -Gx accelerations, may allow the rear seat
passenger to strike the seat back ahead if he is carried forward
by inertial forces. In certain instances, seat displacement in
auto accidents can cause submarining and subsequent internal and
spinal injuries to front seat occupants.

- Such observations, especially in light of Swearingen's (31)
comparison of the light airplane experience to the motor car with
potentially similar velocities, leads one to appreciate the
importance of determining the characteristics of liight-airplane
accidents. Furthermore, the nature of airplane accidents can be
influenced by operational and structural factors which may be
changing over the years as light airplanes gain more speed and
sophistication, operate in more adverse weather conditions and
challenge the proficiencies of the pilots involved to a greater
extent.

Some delineation of the typical forces intrinsic to the
common light airplane accidents would provide a basis for
determining injury mechanism and the seat's role in those events.
The General Aviation Safety Panel, GASP, postulated certain
parameters that it considered representative of the light
airplane accident, for purposes of conducting sled tests on
various general aviation airplane seats (4,9). A downward
vertical velocity that was sufficiently great to cause a
resultant force vector at impact to approximate 60 degrees below
the plane of the floor was chosen by the panel.


INJURIES TO SEAT OCCUPANTS OF LIGHT AIRPLANES

INTRODUCTION

There is continuing concern for the weli-being of occupants
of light airplanes that are involved in accidents. Engineering
technology provides for design changes in airframes that may
significantly reduce or even prevent injuries to persons involved
in such accidents (24,27,32).- Many of these changes can be
incorporated without adversely affecting the efficiency of the
vehicle and without incurring unreasonable costs. Definition of
the specific mediators of injury and their relative importance is
necessary so that the most rewarding improvements in airplane
design can be implemented. The airplane seat, because of its
proximity to the occupant, is expected to mediate injury as well
as attenuate injury, and may be an integral part of the restraint
system. For this reason it is important to define the role of the
seat with respect to injuries sustained by its occupant (3,23)
To this end a selected series of light-airplane accidents was
studied in an effort to better understand the relationship of
light-airplane seats to the injuries sustained by their
eccupants.

BACKGROUND

Two complementary lines of research contribute to the
understanding of this problem. Laboratory experiments conducted
under controlled conditions establish limits of structural
tolerance of seats as they are exposed to forces applied through
such mechanisms as test track accelerators. Anthropomorphic
dummies, electronic instrumentation and high speed photography
can be used to define much of the mechanics involved under these
conditions (4). A common limitation in such approaches is the
uncertainty that the parameters selected for the experiment truly
reflect the circumstances operative in an airplane accident. The
other research approach depends on observations derived from
actual airplane accidents which are representative but
correspondingly limited by the absence of needed measurements of
energy transfers and accelerations (18,21,22).

Recent publications (19) have described airline seats as a
significant cause of injury to passengers because the seats may
become detached from their moorings during an accident sequence.
It has been suggested that seats should perform better if they
were aft facing so that forces were applied through the seat back
over the largest available area of contact with the occupant (6).

1


Stratification is one method to control biasing factors su
as energy level (17). Data collected in this study was
adequate to reliably stratify most accidents into high and icw
energy categories. Impact angle was estimated for a few of the
accidents, but information on stopping distance and estimated
speed were not available. If this information were available,
the relationship between seat failure and injury severity could
be examined for the two subgroups, high and low energy accidents.
It is hypothesized that, if an adequate sample were available,
there would be no association between seat failure and injury
severity in low energy accidents. Humans sustain -injury at much
lower energy levels than are needed to damage a seat and common
forces tend to separate man and seat. At higher energy levels
both the seat and its occupant are likely to be damaged.

TABLE IV

INVESTIGATORS’ DETERMINATION OF SEAT ROLE
IN INJURY CAUSATION

RESPONSE FREQUENCY PERCENT
SEAT ADDED TO INJURY 9 10
SEAT LESSENED iNJURY 7 8
SEAT MADE NO DIFFERENCE 70 82
TO OCCUPANTS INJURY

One field on the FAA form 8025-3 asked the investigator to
determine if the seat failure had added to the occupant's injury,
ameliorated injury, or didn't make any difference. For 35% of the
eccupants this field was blank. Of the remaining cases 10%
reported the seat added to the occupants injury, 8% indicated
that the seat distorted and cushioned the impact, 82% reported
the seat did not make any difference in the occupant's injury.

14


In this study we examined injury experience and impact
findings in actual accidents involving light airpianes.
Relationships between injury pathogenesis and seat causation are
described.

METHODS

Fifty-five light airplane accidents were selected for this
study. The accidents occurred between April 1981 and Aprii 1986.
The maximum certificated gross weights for these airplanes were
12,500 pounds or less. The terms “aircraft accident", "fatal
injury," and “serious injury" were used as defined by the NTSB
(23).

Although it woulc have been ideal to analyze the entire
population or a true random sampling of light airplane accidents
as part of this study, practical limitations did not permit this.
The proportions of makes and models cf aircraft represented in
this series correspond to those of the general aviation fleet
(8). The sample was composed of accidents in which the energies
were sufficient to truly test seat performance and cause injury.
The very low energy incidents, such as a flat tire developing
early in the take-off roll or the low velocity ground loop in
which no significant damage occurred were excluded. At the other
end of the spectrum, the kind of accident in which the danage is
extremely severe and much of the evidence is destroyed by impact,
fire or other environmental misfortune was also excluded. The
terms "survivable" and "non-survivable" have been applied to
delineate the polarization in this concept (11,20,27,32). The
case selection criteria included the following:

1) Must be an accident according to NTSB definition

(22)
a) plane must have sustained substantial damage
or
b) at least one occupant experienced severe or
fatal injury.

2) Must be a light airplane (12,500 pounds or less)

3) Wreckage not destroyed by fire so that seat and

restraint evidence available.

4) Must be a survivable accident

a) deceleration forces do not exceed human
tolerance.

b) some portion of the passenger cabin remains
substantially intact.

The observations of the available evidence at the
accident site were made by aviation medical examiners (AMEs)
National Transportation Safety Board or Federal Aviation
Administration (FAA) investigators while post-mortem studies were
usually conducted by county cr state medical examiners or
pathologists.



One might suppose that any damage to the seat, however
trivial, would be noteworthy and capable of contributing to
significant injury of its occupant. However, the mechanics of
some seat deformation and external damage clearly provide for the
attenuation of applied energy and thereby reduce injury.
Individual cases report seat damage which is not clearly related
to any injury. The appropriate criteria for seat failure becomes
correspondingly more complicated.

The authors established the seat failure criteria described
earlier and depicted in Fig. 2 based on the evidence in this
series and the relevant literature (14). In the majority of seat
failures, the seats became detached from their moorings allowing
for dislocation with respect to their normal positions in the
aircraft. The seats that detached or failed in such a way that
they allowed the restraint system to become ineffective were
considered a separate category. This was done in recognition of
the importance that appropriate restraint could assume in. such
circumstances. In the typical case from this grouping, injury
was sustained by the occupant as he separated from the seat and
impacted other forward cockpit structures.

Changes in restraint attachment points and other
modifications of the restraint system are likely to be more
direct and effective points of intervention than efforts in seat
modification.

Similarly, it is difficult to. determine if the cases in
which a ‘ear seat occupant struck the rear of a forward seat
represent seat failure as tabulated in Fig. 2, cr whether rear
seat restraints and appropriate spacing between seats are the
proximate problems. We believe that it will be more fruitful to
consider the restraint system as a separate but closely related
problem which is best solved by interventions that directly
address restraint system elements rather than the seat. That
approach implies that anchor points for belts shoulé be
determined in a context that provides for the most secure
performance of the restraint system without favoring the seat as
an attachment point over any other appropriate structure.

It is unlikely that seat failure would be related to severe
or fatal injury by simple, direct mechanisms that allow for
observation of seat damage as a reliable marker of seat-induced
injury. Comparisons between seriously and fatally injured
occupants of failed and intact seats suggest that such a simple
relationship does not exist in this series. There were
approximately equal numbers of failed and intact seats occupied
by persons seriously or fatally injured. Seat failure alone is
not a reliable marker of seat-induced injury.

20



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DIST AVAIL AND/OR SPECIAL
DATE ACCESSIONED
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DISTRIBUTION STAMP
DATE RETURNED
DATE RECEIVED IN DTIC REGISTERED OR CERTIFIED NO.

PHOTOGRAPH THIS SHEET AND RETURN TO DTIC-FDAC

DTIC FORM 70A
HAR 86

DOCUMENT PROCESSING SHEET

PREV.OUS EDITION MAY BE USED UNTIL.
STOCK IS EXHAUSTED.


Most of the observations were made by aviation medical examineis
(Fig. 1). In the fields of interest, there were no significant
differences among responses from the several] groups of observers.
Regional flight surgeons rarely reve~sed or amended the essential
observations.

Yigure 1 describes the sources of observers as follows:
Aviation medical examiners (AMEs) investigated 62% of the
accidents, representatives of a Flicht Standards District Office
(FSDO) or a General Aviation District Office (GADO) investigated
27% of the accidents, and investigators dispatched from the Civil
Aeromedical Institute (CAMI) investigated 11% of the accidents.
NTSB accident reports were obtained when available and used to
supplement data submitted on FPAA-form 8029-3,

FSDO/GADO
27%

FIGURE 1 - SOURCES OF OBSERVERS



For purposes of this study, based on a consideration cf
relevant literature, the authors defined the presence of one or
more of the following conditions as seat failure
(1,4,5,6,7,11,15,25,27,30,32,33).

1. The seat detached from its attachment points in such a
way that it rendered the restraint system inoperative or
ineffective. Typically this condition developed when the lap belt
was attached to the seat.

2. The seat detached from its attachment points allowing fer
displacement of the seat from its original position. Instances
ef minor deformations, cracks, and failures in one or more
attachment points that did not result in movement of the seat
from its original position were excluded from the seat failure
population.

3. Phe seat acted as an impactor causing injury to an
airplane occupant. The typical example of this kind of failure
was the circumstance in which the rear seat passenger moved
forward striking a part of the back of the seat ahead.

4. The seat failed to protect its occuparit from impactors
intruding into the volume of space designed for the occupant.

Each case was reviewed at CAMI with the goal bei.g to
extract observations regarding force directions and magnitude,
nature of the injuries and causal relationships.

RESULTS

All the desirable information suggested above was not
submitted in every case. Autopsy protocols were often missing on
fatal cases. Many observers did not respond to all questions and
there is some suggestion that the questions were not aiways
interpreted in the same way. Table I describes the kinds of
documentation that were submitted.

TABLE I
INFORMATION SUBMITTED FOR 55 ACCIDENTS
NUMBER OF CASES WITH 8025-3 .0......c0. ccc eee ese eceseeneeetereeeseenseeteeee 5S
NUMBER OF CASES WITH PHOTOGRAPHS .......-..0c0seccceeeeeeeceeneeeeeeees 36

NUMBER OF CASES WITH AUTOPSY PROFOCOLS...............00e-e eee eee vi

NUMBER OF CASES WITH 8025-2, REPORT OF MEDICAL
FINDINGS IN AIRCRAFT ACCIDENTS ...0.0 2. ec cceceecec cece eeceeseenseeeeeeeeceeeee 15



24.

25.

26.

27.

28.

29.

30.

31.

32.

33.

Pennybaker AL, Ross JW, Wilson GW, A Summary of
55 rthiness Information for Small Ai es, FAA-TR-592-
120A FE 1973.

Robertson LS, Estimates of Motor Vehicle Seat Belt
Effectiveness a Use: lication for Occupant Cras'
Protection. American Journal of Public Health Sept, 1976,
Vol 66 #9 pp 859-864.

Siegal s, Non-Parametric Statistics, McGraw-Hill Book
Company, New York, NY 1956.

Snyder R, Crashworthiness Investigation of General Aviation
Accidents, Society of Automotive Engineers Business Aircraft
Meeting, Wichita, KS April 8-11, 1975 SAE #750537.

Snyder RG, A_Case of Survival of Extreme Vertical Impact in
the Seated Position. FAA-AM-6219.

Snyder RG, Occupant Impact Injury Tolerances for Aircraft
Crashworthiness Design. Society of Automotive Engineers,
National Business Aircraft Meeting, Wichita, KS Mar. 24-26,
1971 #710406.

Snyder RG, Occupant Restraint Systems of ometive
Aircraft, and Manned Space Vehicles. In Gurdjian ES Ed.
Impact Injury and Crash Protection. Chas. E. Thomas Pub.
1970. p. 497.

Swearingen JJ, General Aviation Structures Directly
Responsible for Trauma in Crash Deceleration. FAA-AM~71-3.

Turnbow JW, Haley JL, A Review of Crashworthy Seat Design
Principles. SAE Air Transport and Space Meeting, New York,
NY. April 27-30, 1964.

Underhill B, McCullough B, An _Ener Absorbing Seat Design
for Light Aircraft _, Piper Aircraft Corporation. National
Business Aircraft Meeting, Wichita, Kansas. Mar 15-17, 1972
#720322.

26


12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

Haddon W, Baker SP, Injury Control, In D.Clark and B
McMahon, Eds. Preventive and Community Medicine. Boston,
Mass. Little Brown and Co., pp. 109-140. 1981.

Kinlberg JK, Multivlicity of Injury in Automobile
Accidents. In: Gurdjian ES, Injury and Crash Protection pp.

5-26. 1970

Laananen DH, Simula Inc., Aircraft Crash Survival Design
Guide; (Volume IT) Aircraft Crash Environment and Human

Tolerance USARTL-TR-79-22 (A-E); 1980; Applied Technology
Laboratory, U.S. Army Research and Technology Laboratories
(AVRADCOM), Fort Eustis, Virginia 23604.

Laananen DH, Simula Inc., Aircraft Crash Survival Design
Guide; (Volume IIT) Aircraft Structural Crashworthiness

USARTL-TR-79-22 (A-E)+ 1980; Applied Technology Laboratory,
U.S. Army Research and Technology Laboratories (AVRADCOM),
Fort Eustis, Virginia 23604.

Laananen DH, et al Simula Inc. Computer Simulation of an

Aircraft Seat and Occupant in a Crash Environment. March
1983 (SOMLA)

McKinlay, S.M. de: n_and analys of ob ional

study. A review. Journal of the American Statistical
Assocjation 70. 503~523.

McMeekin RR, craft Accident Investi ion In DeHart R
Ed., Fundamentals of Aerospace Medicine Lea & Febiger,
Philadelphia. 1985 p. 796.

Nolan, D. Airline Safety:The Shocking Truth. Discover,
Oct. 1986.

NTSB General Aviation Crashworthiness Project Phase i, 1985

NTSB Gener. viation Crashw hiness Project - Impact

Severity and Potential Injury Prevention in General Aviation
Accidents Phase 2 NTSB/SR-85/01

NTSB General Aviation Crashworthiness Project Phase 3
Acceleration Loads and Velocity Changes of Survivable General

Aviation Accidents. NTSB/SR-85/02.

NTSB Regulation, Part 830.1 and 830.2, Subpart A, Code of
Federal Regulations

25


In a recent series of reports, The National Transportation
Safety Board (NTSB) defined relationships between the opportunity
for survival in light-airplane accidents and the impact angle or
airspeed of the airplane at its major impact point (20,21,22).
These reports suggest that survivable experiences tend to cccur
when the impact angles are small and the vertical accelerations
do not predominate. An envelope of survivability was estimated to
be 45 knots at 90 degrees of impact angle, €0 knots at 45
degrees, and 75 knots at 0@ degrees.

The detailed analysis of injury sustained in light-airplane
impacts would also contribute to an understanding of the

mechanisms involved. While many similar injuries can be
inflicted in a variety of ways, there are certain characteristic
findings which suggest likely mechanisms of injury. For

example, compression fractures of vertebral bodies in the low
thoracic and lumbar spine typically occur as a consequence of
forces acting approximately parallel to the long axis of the
spine (28). Forces acting perpendicularly to the spine are more
likely to produce a translational displacement of vertebrae.
These forces can also produce rotation and extension of the
spine. Similarly, a typical finding in light~-airplane accidents
involves blunt trauma applied to the head affecting the face
predominantly and typically resulting from striking the head
against a control wheel, instrument panel, console or other
cockpit structure (18,31). These face and head injuries suggest
mechanisms that proceed independently of seat performance unless
the back of a forward seat serves as a contact point for a rear
passenger.

The seat may contribute to head injury in at least two ways.
When the seat is a critical link in the restraint system which
fails because of a deficiency in the seat or when the seat
deforms and allows the body to move out of position for correct
application of restraint, head injury may result. Methods of
injury analysis are limited by the lack of detailed observations
from the common light airplane accident that would elucidate the
mechanism of injury and the impact points of the cockpit environs
(2). This is true even in the cases in which autopsy examinations
are conducted. Coordination between the field investigators and
the pathologist performing the examination is frequently limited
and not timely enough to ensure that these issues are regularly
treated. Additionally, many fatally injured occupants of light
airplane accidents are not autopsied. Even less information is
available on occupants who are seriously injured but not killed.


A tabulation of the occurrence of injury to each anatomic
region as a percentage of all observed injury is presented in
Table VI. Tabulation of autopsy data regarding injury revealed
what one would expect, that the most ecbvious and compelling
injuries were consistently noted. Those more subtle injuries,
such as injury to the spine, were not reported as often as in
living patients. Injuries to the head and chest accounted for a
large portion of the injuries in both autopsy and clinical injury
reported in this series (13,14). These injuries are unlikely to
be mediated by the seat, except in cases in which the seat caused
failure of the restraint system.

TABLE VI

PER CENT OF INJURY BY ANATOMIC
REGION OF BODY
(Derived from 11 autopsies)

REGION FREQUENCY | PERCENT
[_recion | Frequency | reRcent
UPPER 9 8
EXTREMITIES j
LOWER
EXTREMITIES 16 4
HEAD 30 27
THORAX/
ABDOMEN 51 “6
SPINE/PELVIS 6 5
TOTAL 12 146

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Page 6

{ian}

FAA Form 8025-3


Codes for injuries and injury causes: L
Record name, and sex as available.
3. Seat Postion - Record sosition as designated in number 6,
Cabin Seating
Z = ankeoun
b. Height and Weight — record for each occupant (such 23 60"
165 tbs)
© Severity of injury ;
~ fatal i
- serious with more than 16% residusi disebility expected.
serious
minor
none
unknown
Skull and Brain
blunt trauma with multiple fractures of skull — or
partial decapitation
blunt trauma with lesser degree of skull fracture than A
biunt trauma with small skull fracture
Penetrating trauma with fracture of skull
penetrating trauma without fractures
abrasions and lacerations — severe
abrasions and lacerations ~ minor to moderate
brain laceration with fractures fk
brain laceration without fractures
severe brain contusion and/or bleeding
mild to moderate brain contusion and/or bleeding
fo significant abnormalities
unknown

Nzzonn7

poiere > pees

frat

TNXAL-ITATMOOD »

Palvis
~ simple fracture

Cc ONxmoO®

NXErR © — TANMONG>Y Nxrn~e-LomMMoOGD

teetcreeececnt

reretenes

multiple fractures

contusions without fractures

~ rupture of bladder
— laceretions and/or abresions

= no significant abnormatities

~ unknown

.ega(Designate & for teft; Fi tor right; U for unknown side)

— traumatic am. utation below hip

‘traumatic smputstion below knee
compound/comminutad fractures upper teg
compound/comminuted fractures lowes leg
simple fracture upper leg

simple fracture lower leg

fracture of dislocation at ankle

fractures in bones of feet

contusions and abrasions without fractures
sprain, strain with discomfort

dislo~stion hip

dislocation knee

No significant abnormalities

unknown

and Spinat Cord
‘transection of the spine

fracture/fractures neck without cord damage
frecture/fractures neck with cord damage
fracture/fractures thoracic spine without cord damage
fracture/fractures thoracic spine with cord damage
fracture/frectures lumbar spine without cord damage
fracture/fractures lumbar spine with cord damage

~ trum i
A = bina grougna with serious fractures, maxilla and/or compression fracture/fractures cervical vertebrae,
B ~ blunt trauma with moderately serious fractures, such no cord damage x
2s mandible, maxilla and/or ather bones - tho cord darn fracture/fractures thorecic vertebrae,
- Z i ji
C= blunt trauma with minor fractures, mandibe, note, ee See cureli ‘ .
D — penetrating trauma with fractures no cord damage
E — penetraring trauma with permanent cye injury — servical strain
F — penetraung trauma wicscut fractures = thoracic strain
G — abrasions and lacerations severa — tow back strain i
H — abrasions and lacerations minor to moderate = no significant abnormatities
X = no significant abnormalities — unknown
2 — unknown
f. Arms (Designate L for left: R for right; U for unknown side) CAUSE OF INJURIES
A — traumatic amputation below shoulder
B — traumatic amputation below elbow 1, Shoulder restraint
€ — compound/comminuted fractures upper arm A — caused contusions and fractures of chest
D — compound/comminuted fractures lower arm B — cused abrasions and contusion of chest
E — fracture’fractures upper arm c= and marks on chest withour injury
F ~ fracture/fractures lower arm BD - jury
G — fractures wrist £ — instalied but not used
H ~ fractures fingers F — net instalied
1 = fractures thumb. Z — unknown
J = dislocated shoulder
K ~ disiocated etbow m, Lap belt
L — dislocated wrist A
X = no significant aonormatities Be
Z = unknown
9 Chest ‘ $c
A - bt yma with cr i A -
pee na Tonge th crushing of opening of chest cavity, E — instalied but not used
8 — biunt zrauma wath fractures of sternum and/or ribs — 2 — unknown
‘not fethai in itself
C — blunt trauma, minor without frectures n, Seat
© — penetrating wound in chest, 2 or more inches in diameter As injuri
& — penetrating wound in chest, lexs then 2 inches in diameter B — failed badly, did not add to injury
F — waumatc rupture of heart C — partially broke, adding to injury
G — tearing or rupture of aorta D — partially broke, not adding to injury
H — contusion of heart — non-ethal E — distorted and cushioned impsct
1) — contusion of tungs — non-iethal F — caused no injury
J = no significant finding Z = unknown
K — closea pneumothorax
— bleeding into pleural cevities 0. Cockpit/Cabin Structure
= no signttican: abnormalities
— unknown During impact occupant:
h. Abdomen — struck yore

— abdominal cavity widely opened
abdominal wali has penetrating injury
contusion of abdomen with wall intact
internat bleeding severe

internai bleeding moderate

internal bleeding slight

contusion with rupture of internal organs
contusion with abdominal symptoms
contusions and abrasions without internst symptoms
fo significant abnormalities

~ unknown

rerrrded

NxX-ZTONMOODDSD Nx

FAA Form 8025-3 {1-813

A
B
c
5
E
F
G
H
'

4
K
z

— struck instrument panel

— struck back of seat

— struck partition or divider

was struck by flying object

made impact with floor

made impact with rudder pedals

made impact with windscreen or window

struck cockpit — cabin structural members — posts, etc.
struck other objects, specify
struck no objects

unknown

Page 7


franslational forces applied to the spine in the X axis
could have caused spinal injury as plausibly as Z axis forces
tending to compress the spine from mechanisms likely to have been
mediatea@ through the seat. The evidence, then, is equivocal with
respect to defining the injury population clearly caused by seat
acticns. However, it is possible to identify the general
distribution of injuries in this series. Table VI presents the
frequency of injury affecting the general anatomic regions of the
body. Obviously, many occupants sustained multiple injuries.
Each reported injury was tabulated so that the total number far
exceeds the number of occupants at risk. Perhaps the most
significant observation related to this information is that head
injury predominates. The critical vital functions exposed by
head injury and the vulnerability or propensity toward lethal
outcomes make head injury even more important than the numbers
themselves might suggest.

Table VI presents the injuries described through autopsy
examination. These differ from the previous findings partly
because of the routine procedures applied at autopsy which favor
finding some diseases rather than _ others. Backache and
ligamentous sources of pain would be identified in the clinical
patient and not in the deceased patient. However, head injury
still persists as numerically important being second only to the
combined torso injuries. Spinal injury was not prominent in the
autopsy data.

Injury causing structures in the airplane are tabulated in
Table VII. The noteworthy observations are that the control
wheel and instrument panel were identified more frequently than
other structures. The seat was identified as the impactor only
8% of the time. As was suggested earlier, the proximate cause of
injury in these events depends on restraint effectiveness, space
allocation and other elements.

SUMMARY

This series of light airplane accidents was examined in an
effort to demonstrate the role of seats in the genesis of injury
in seat occupants. Case selection attempted to include only
those events in which significant accelerations challenged the
seats' effectiveness without imposing unrealistic, extreme
demands on the seats and their occupants. No reliable marker of
energy level was found in the data collected to control the
energy level as a confounding variable to allow clarification of
the finding that large accelerations tend to injure people and
damage seats as well as most other structures regardless cf the
other inter-relationships that might be involved.

22



Technical Report Documentation Page

1. Report No. 2. Government Accession No 3. Recipient s Catalog No. |

DOT / FAA-AM-89 - 2
4. Tithe and Subntle 5. Report Dote
[ve 1989 :

9 Organization Code

Fo

INJURLES TO SEAT OCCUPANTS OF LESHT AIRPLANES

AAM-610
__ 1G. Performng Organization Report No
7. Auther's!
Eugene J. Colangelo, M.D. and Julie C. Russell, M.P.H.
9. Pertorming Organization Name and Address 10 Work Unit No (7 RAIS)
FAA Civil Aeromedical Institute { :

P-0. Box 25082 IVT Contract ar Grant No. f
Oklahoma City, OK 73125

13.” Type of Report ond Penrod Covered

12. Sponsoring Agency Nome ond Address

lof fice of Aviation Medicine TECHNICAL REPORT
(Federal Aviation Administration {
800 Independence Ave., SW 14. Sponsoring Agency Code

Washington, D.C. 20591
15. Supplementary Notes

This work was performed under task AM~B-88—-T( X-57

V6. Abstract
A series of 55 light-airplane accidents was examined in an effort to demonstrate the
role of seats in the genesis of injury in seat occupants. Cood engineering design of
airplane seats is an important related issue which is not treated in this study.
Case selection attempted to include only those events in which significant but not
extreme accelerations occurred. Ten of the fifty-five cases involved joint failure
of seats and restraint systems. The majority of the observations were provided by
aviation medical examiners who were typically very highly motivated practitioners of
medicine with special interests and accomplishments in aviation. The other cases
were reported by FAA accident investigators.

No reliable marker of energy level was found in the data collected to control the
finding that large accelerations tend to injure people and damage seats us well as !
imost other structures regardless of the other interrelationships that misht be
involved.

The existence of seat damage does little, by itself, to devine the seat's role in
‘injury causation. Interpretation of injuries established by clinical and autepsy
observations suggests that the large majo ‘ity of injuries are caused by mechanisms
which can proceed independentiy of seat fiiluce. Restraint systems likely play the
more important role.

7. Key Words 18 Distibution Statement
Aircraft accident; airpiane seat failure; jDocument is available to the public through

impact injury; injury mechanism; impact the National Technical Information Service,
acceleration; airplane occupant impactors |Springfieijd, VA 22161
i

een Bee

i
1
i

19. Secunty Clossrf. (of this report) T 20. Security Classif. (of this poge) j 21. No. of Pages | 22. Price

Unclassified Unclassified 26 |
_t

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


In ten of the cases, our contributors responded with arrows
drawn to depict the forces as suggested above. Each of these
arrows was resolved into a horizontal and vertical component
which could be added vectorially to approximate a mean vector for
that event. Additionally, some sense of the relative role of
vertical forces compared to longitudinal forces was implied.
Transverse forces producing yaw were not reported as being
predominant and were not similarly analyzed for relative
magnitude and direction. Some components of transverse force
were probably reflected in the depictions of movement in the
plane containing the longitudinal and vertical axes of the
aircraft.

+Y values
\ +X values

Cc

+ X axis

-X values

~ Y values

Y axis

FIGURE 4, FORCE VECTOR DIAGRAM CN \ARTFSIAN COORDINATES

10


TABLE Ii
FORCE VECTORS

HORIZONTALIVERTICAL | ,RELATOE RESULTANT

X axis Y axis VECTOR

1.0.
1.0.
1.0.
1.0.
1.0.
1.0,
10.

Each drawing submitted on 20 accidents was analyzed. The
remaining 35 cases contained insufficient information. Results
shown in Table II indicate that the magnitude of the combined
vertical forces is about one third of the magnitude of the
combined horizontal forces. The mean angle of the resultant force
vectors is estimated to be 15 degrees below the horizontal axis.

12


NOTICE

This document is
Departrent of

disseminated under the sponsorship of the
exchange.

Transportation in the interest of information

The United States Government assumes no liability for
its contents or use thereof.



8. Lapbelt and Upper Torso Restraint Findings.
Complete this table. Enter findings using codes given betow. Identify each restraint system by seat position.

LAP BELT UPPER TORSO RESTRAINT INERTIA REEL
tachment r
parti, | Used | inboatdkaboard | Function | Type Used agetecnment |g | Function | installed } Function
a b © 3 2 t 9 h i L k 4
1
Codes for restraint findings:
2. Seat position: record position as designated in ci b. Aft Attachment
‘seating. A ~ to seat only
- th
LAPBELTS B — to wall or overhead
Yes No — installed, not used amas
b. Used” he -
N—notinstalled Z — don't know D — to frame wia cables
Z~ unknown
LAPBELT ATTACHMENT POINTS 1. Forward Attachment
¢. Inboard attachment (right in single or tandem seated A — lapbelt
aircraft ) B — seat
A ~ On seat C ~ floor
B On floor 0 -- console
C - on wall, bulkhead or cansole € = wall
D — via cable to frame Z— unkown
2 ~ unknown, 1 Function
d. Outboard attachment A — held with no problem
A - on se0t B - complete faiture at aft attachment
8 — on floor C —comptete tatture at forward attachment
C — on wall, bulkhead or console D -- complete failure both attachments
© — via cable to frame £ — failure of hardware other than attachment
2 — unknown © — partial failure of webbing
e Function G — complete taslure of webbing
A — heid with no problem H - does not pertain
6 — complete failure at right attachment Z — unknown
C - complete failure at left attachment {Use narrative comments for clarity)

D ~ complete failure both attachments

E -- failure of hardware other than attachment (explain) INERTIA REELS

F — partial failure of webbing k. Instatled. Yes. No

G — complete failure of webbing 1. Function

Z ~ unknown A — held with no problem
UPPER TORSO RESTRAINT (UTR) B — failed to latch

C ~ partially latched but held

f Type: 0 - double ialegamnaal D - partially tatched, but did not hold
9. Used: Yes No ~ installed but not used & — tanure of reel housing
N—notinswalled = Z — unknown F — indication of functional problem in reel before

accident
Z — unknown

{Explain with narrative comments to clarity any
finding)

FAA Form 8025-3 (1-81) Page 5



The likely mechanism explaining this disparate relationship
involves the occupant in "survivable" accidents selected by this
series experiencing inertial forces which tended to separate him
from the seat resulting in not loading the seat and in preventing
contact with the seat. It would thereby tend to lose its
opportunity to serve as an impactor. In such circumstances, the
seat would appear to be successful merely by remaining attachec
to the airframe without having to sustain the added forces
introduced by the occupant's mass. If the population in this
series were weighted toward those occurrences in which there were
predominantly vertical loads applied to the seat and its
occupant, the results may have been different. The available
data would indicate that the seats’ influence on injury severity
is relatively small. It is likely that the injuries caused by
factcrs other than the seats would overshadow findings of seat
induced injury.

The related issue of high versus low energy impact was
subject to examinaticn by using the vectors described as being
less than 15 degrees to identify low energy events in comparison
to those cases in which the resultant vectors exceeded i5
degrees. NTSB findings in (20,21,22) suggest that this technique
can assist in identifying the high energy impacts. Table III
presents this tabulation to show the expected increase in injury
with high angle events. A corresponding increase in seat failure
suggests that injury and seat failure may both be dependent or
another variable, very probably the magnitude of the energy
transfer and the associated large accelerations. The question of
causal relationships between seats and occupants’ injuries is
directly addressed by responses presented in Table Iv. In 10% of
the cases the seat was considered to have added to the injury; in
8% the seat attenuated or diminished the injury while in 82% the
seat appeared to play no role in inflicting the cbserved
injuries. This finding agrees with Cannon's (2) study which
points out the difficulty of establishing a causal relationship
between a particular structural failure and coincident injury.

An analysis of the injuries sustained by seat occupants was
attempted in an effort to examine whether or not the nature of
the injuries might help define the role of the airplane seat in
causing or attenuating those injuries. Unfortunately, in the
vast majority of the injuries reported, the precise pathogenetic
mechanism for the injury was never established. Consequently,
injuries to the spine and pelvis described by the existing data
from this series could have developed from a variety of
mechanisms that could not be differentiated.

21



AD-A207 579

DOT/FAA/AM-89/3

Office of Aviation Medicine
Washington, D.C. 20591

Injuries to Seat Occupants
of Light Airpianes

Eugene J. Colangelo, M.D.
Julie C. Russell, M.P.H.

Civil Aeromedical Institute
Federal! Aviation Adminisiration
Okiahoma City, Oklahoma 73125

FEBRUARY 1989

Technical Report

This docurnent is available to the public
through the National Technical Information
Service, Springfield, Virginia 22161.

US Department
of Transportation

Federal Aviation
Administration

es


|

SEAT AND RESTRAINT CRASHWORTHINESS DATA

Accident Identification

DATE: LOCATION:

AIRCRAFT MAKE & MODEL: IN-NUMBER:

1. Indicate attitude of aircraft at its time of maximum impact.

nose fAYANSSs

as? woe 18° FLAT

6506000600060 © om __
KK Kw RR &

60° 40° 20° FLAT 20° 40°

COO GSO on
vaw BEES EWR

(Lateral
Impact 30° 20° 10° 10° 20°

Forces) Ch Oe Oe 5 eC] eX] 0 Other —____

Additional comments on phase of flight, aircraft speed, attitude or peculiarities of impact that reveal
forces acting on aircraft and occupants. Sketch if indicated,

ROLL

2. Estimate the survivability of impact. (Check one)

Ci survivabie G Partly survivable oO ‘Survivai by chance og Non-survivable

3. Damage to OCCUPIABLE area. Record by entering check in appropriate place.

Cabin
Structure Forward | Top | Bottom | Right | Left Aft
Use the following criteria:
Intact Intact — No spparent damage.
Distorted — Damage is confined to slight bending,
wrinkling or twisting, however, the structure retains its
Distorted size and shape.
Bent/Partisity Collapsed ~ Members are bent, twisted
Bent/Pertty or deformed to that the structure, as a whole, has
Collapsed changed in general shape and decreased in volume.
Collapsed/ Collcpeed/Buckled — The structure retains little of its
Buckled original shape or volume.
Torn Free/Disintegrated — The structure is torn away,
Torn tree/ mangled, or broxen into fragments.
Dismntegrated
1. L

FAA Form 8025-3 (x-e1)

Paget



The existence of seat damage does little, by itself, to
define the seat's role in injury causation. Interpretation of
injuries established by clinical and autopsy observation suggests
that the large majority of injuries are caused by mechanisms
which can proceed independently of seat failure. Restraint
systems likely play the more important role.

CONCLUSIONS

1. Head trauma represents a major manifestation of life-
threatening injuries observed in this series. These injuries
usually resulted from impacts with objects other than the seats.

2. The seat occupants in this series experienced inertial
forces estimated to be oriented approximately 15 degrees below
the longitudinal axis of the airplane.

3. Seat damage per se is not a reliable indicator of injury
sustained. The function of the seat may be subtle and indirect so
that injury may result from mechanisms in which the seat's
contribution is not apparent.

4. The seat's influence on injury severity is relatively
small. It is likely that injuries caused by factors other than
the seat overshadow findings of seat induced injury.

5. Even though the seat was implicated as a cause of injury
in only a small minority of the cases, optimum crashworthiness
suggests that seats be considered as a part of the energy-
attenuating systems to be designed into the airframes.

6. The presence and use of upper torso restraints can

improve the injury experience by reducing the likelihood of head
injury.

23


Figure 2 describes seat failure modes with seat detachment being
the most common, occurring in nearly 3/4 of seat failures.
Partial detachments without major seat dislocation occurred
frequently and are included in this group. Out of 133 occupied
seats, 52 were classified as failed. Figure 2 illustrates the
Proportions of failed seats falling inic four broad categories of
seat failure. The categories are defined as follows:

A. Seat detached and caused restraint system failure ~ 10
(19%)

B. Seat detached only - 28 (54%)

Cc. Sack of seat as impactor - 11 (218%)

D. Seat failed to protect cccupant from intrusion by other
objects - 3 (6%)

Seat failure events are ccunted in one category only, the
_ gategory describing the most noteworthy failure.

FIGURE 2 - SEAT FAILURE MODE (52 SEAT FAILURES)


Figure 4 is a drawing of an airplane superimposed on 32
Cartesian coordinate system having an x axis parallel to the
horizontal and a vertical y axis perpendicular to the horizontal.
The x axis is parallel to the longitudinal aris of the airplane
while the y axis is paraliel to its vertical axis. The arrow
drawn in by the observer to represent the direction that inertial
forces moved the seat occupant can be inserted as Line 4B in
Figure 4. As in any other conversion from polar to rectangular
quantities, the vector AB can be represented by equivalent values
ef x and y or equivalent vectors BC and CA. The reader is
reminded that the use of "x" and "y" in this context should not
be confused with the common use of these letters to describe
acceleration directions applied to aircraft occupants.

These observations and the corresponding sense fer the
relative influences of horizontal and vertical forces can be
presented as in Table IT. Based on the assumption that the
horizontal component, which was always the larger one, could be
assigned a value of one arbitrary unit, the relative influence of
vertical forces could be expressed in relation to that unit. The
arrows depicting the forces acting on seat occupants are
presented as polar quantities in the right half of Table IT
while the left half presents the corresponding rectangular
equivalents. Analysis revealed that the ratio of averaged
vertical forces to averaged horizontal forces was 0.28/1.00.

LL