‘With impact, the protoplasm is seen meeting a
relatively nonyeilding structure (Figure 4). Ac-
cording to long-established laws of physics, either
the structure undergoes rearrangement during
deceleration, or the protoplasm gets rearranged,
or some rearrangement in both occurs.

Therefore, the third principle of delethaliza-
tion is concerned with producing, during im-
pacts of living and nonliving material, the major
amount of the alterations in the nonliving sub-
stance.

Third Principle: Provide a means of produc-
ing a prescribed budy-segment deceleration dis-
tance within the portions of the cockpit structure
likely to be struck by the respective body seg-
ments during impacts.

Note how the peak g force in Figure 5, which
represents a deceleration force generated by a
relatively nonyielding substance (hard wood);
far exceeds that generated in the “sandwich”
material (Figure 6). These data are representa-
tive of that being obtained by Mr. Swearingen at
CARI, in a continuing study of: (1) The upper
survival tolerances of human beings to impacts;
and (2) The best combinations of energy-absorb-
ing materials for survival under specific condi-
tions?

18 FEET / SECOND

+— |809

HEAD IMPACT
WITH WOOD BLOCK
3 INCH THICK

oem
10 MILLISECONDS

Fieure 5.

15 FEET / SECOND

HEAD IMPACT WITH
“SANDWICH” MATERIAL
3 INCH THICK

—~_+— 499

———
26 MILLISECONDS

Ficure 6.



REFERENCES

Brenavr, Wilfred H.: Design and Testing of Pas-
senger Seats for Crash Survival, SAE Paper 517B,
pp 1-4.

Brucemx, Gerald M., Barnes, Alfred C., and Gueee,
Lee W.: “Injury Reduction Trends in Agricultural
Aviation,” Aerospace Medicine, May 1964, pp 472-475.

. Grka:, Paul W., and Hvetxe, Donald F.: “Causes of

Death in Automobile Accidents,” Journal of the
Michigan State Medical Society, May 1964, pp 851—
354,

. Jurrner, Joseph P.: U.S. Civil Aircraft, Volume 1,

Aero Publishers, Inc, Los Angles, California, 1962,
p 158,

Kurowsx1, Jacos: Crash Injuries, Charles C.
Thomas, Springfield, Illinois, 1960, 1,080 pp.

Leperer, Jerome: Personal communication concern-
ing new delethalized BOAC seat, August 3, 1964.
Pearson, Richard G.: Human Factors Aspects of
Lightplane Safety, CARI Report, 63-35, 1963, 18 pp.

8. Snypex, Richard G.: A Case of Survival of Extreme
Vertical Impact in Seated Position, CARI Report
62-19, 1962, 15 pp.

Snyper, Richard G.: Human Survivability of Ex-

treme Impacts in Free-fall, CARI Report 63-15, 1963,

29 pp.

10. Stapp, John P.:; Design Criteria for Occupant Re-
straint Systems, Proceedings of the Seminar on De-
sign Aspects of Occupant Survivability in Aircraft,
Flight Standards Service, FAA, Oklahome City, Ok-
lahoma, February 11-15, 1968, pp 1-4.

11. Swearincen, John J.: An Analysis of Sitting Areas
‘anid Pressures of Man, CARI Report 62-1, 1962, 10 pp.

12. Sweanrncen, John J., Hassroox, A. H., SNypER,
R. G., and McFapven, E. B.: Kinematic Behavior of
the Human Body During Deceleration, CARI Report
62-13, 1962, 8 pp.

13. Swearincen, John J., Determination of Centers of
Gravity of Man, CARI Report 62-14, 1962, 37 pp.

2

66-4781.


The skull provides very little skeletal contri-
bution to the nose of the human, a situation that
enables the nose to serve as an impact attenuator.
The presence of cartilage in the human nose as-
sists further in this function.

Enshrouding the skull, lying on its fibrous
periosteum, are 51 external muscles (Figure 8).
These muscles, their tendons, ligaments, and fas-
cia lie over various portions of the skull, inter-
digitating with one another, and impart consider-
able strength to the skull-muscle system. They
have considerable impact- attenuation properties.

Ficure 8.

Moving exteriorly from the muscle layers, we
encounter the subcutaneous tissue, comprised of
fat and fibrous elements, and consisting of a
strength somewhat less than that of the muscles.

The skin and its appendages (for example,
hair) constitute the final external layer surround-
ing the skull. As is true of most skin, consider-
able water normally exists in this layer.

Thus, in achieving the accomplishment of the
third principle of delethalization, we have al-
ready been provided by nature with certain phys-
jcal characteristics leading to the progressive at-
tenuation of deceleration energies. Thus, al-

though dozens of g’s of decelerativve force may be
delivered to the face, the brain may receive but
a small portion of these.

Our task is to help nature in its effort to pro-
tect and preserve the brain and return to the
national aviation system as many of those as we
can who, through unfortunate circumstances, are
obliged to experience impacts in their aircraft.
So long as man is mortal, impacts remain a
possibility. Also, even though the major por-
tions of the airframe itself have been designed to
progressively obliterate the impact forces through
erumpling and loss of structural components, the
possibility exists that the internal cockpit en-
vironment may generate high g forces locally.
Therefore, cockpit-interior improvements in de-
lethalized design result in further extending and
enhancing the upper survivability levels accom-
plished through the incorporation of safety fea-
tures int he major airframe design.

III. Mirror-Image Sandwich Construction.

At CARI, we are undertaking an empirical
and theoretical approach to understand better
how impacts may be survived. Involved in this
approach is what appears to be a promising
means of enabling the progressive layers of the
head to “share” successively in the buildup of
impact forces and to avoid, insofar as possible,
excessive loading of a given layer.

Figure 9 shows the “mirror-image” approach
to impact protection. The outer layer of the seat
(or instrument panel) is equivalent in texture
and “softness”. to facial skin, multiplied by a

Ficure 9.



Note that we speak of the survival level, not
merely the much lower “no injury” level. Recent
data concerning several thousand survivors of
free falls, varying in fall heights from a few
inches to thousands of feet, indicate that the
human tolerance to impacts is far higher than
previously suspected." ® This is a happy cireum-
stance, in that we can now approach the “design
for survival” issue in a hopeful state. Philo-
sophically, it appears worthwhile to trade a
certain number of recoverable injuries for what
previously were fatal. protoplasmic alterations.

Our approach to enhancing survivability in
aircraft design is to start with the occupant. For
purposes of illustration, we shall concentrate on
the head.

The pilot's head is a globular structure, having
roughly three external layers adhering to the
skull. The living skull is itself slightly elastic,
and can flex a bit under pressure. The brain is
loosely encased inside, cushioned by the cerebro-
spinal fluid.

Avoiding hazardous punctures of various body
parts have been mentioned. In the head, these
include the globular, fluid-filled eyeballs and the
frontal lobes of the brain. Just below the head,
the larynx is a crucial organ, and certainly, per-
foration of the jugular veins or carotid arteries
is serious. Prior to any anticipated impact, spec-
tacles, if worn, should be removed. Of course, if
he is accomplishing » forced landing over bad
terrain and has a considerable uncorrected re-
fractive error, he will tend to keep his glasses on,
down to ground contact.

The pilot might be found in any one of a
variety of types of aircraft, and each aircraft,
by virtue of its internal dimensions, equipment,
and mission, will require its own approach to
interior survival design.

Actually, one of the most delethalized cockpits
in aviation history is found in the Aeronca C-3
of the early 1930's. Good padding was placed in
tine with the pilot’s head, should an impact occur,
and the instruments were low, and back, under
and the instruments were placed low, and back,
under the padding.

To some extent, pilot physical characteristics
will differ, and our approach will encompass the
170-pound ‘adult male as hypothesized in the
Federal Aviation Regulations (although some

day the Air Force 250-pound standard may be
adopted). CARI anthropologists are studying
the feasibility of obtaining anthropometric data
on pilot populations, in both air-transport and
general-aviation categories, including both sexes
and all age groups. Such data will be invalu-
able in future aircraft design. Already, hun-
dreds of center-of-gravity measurements have
been made on all age groups. This data is es-
sential to proper restraint-system design.**

Viewing the major supporting structural ele-
ments within our subject’s head, we see the skull
(Figure 7), comprised of 29 bones (the total
body has 206). Note that these bones are so
united with one another that a spheroidal vault
of great strength exists. Note also that the lower
jaw is hinged in a fashion that allows consider-
able motion during impact, thus forestalling
fracture or disarticulation.



5. Center-line stand console for switches, tran-
sistorized radios, cirowit breakers, fuel and trim
controls, and other flight operation adjuncts.

6. Internal “back-lighted” instruments (no
“eye-brow” lights).

7, “Organ-bellows” rudder pedals with smooth
sandwich-material lining of the leg and foot “oul
de sac” (some preliminary work with Cessna
Aircraft Company on delethalized rudder pedals
has recently been undertaken by CARI (Mr.
Hasbrook) and Project Little Guy personnel).

8. Impact-absorbing “25-g all-directional” seats
(these can be built for the 250-pound attired oc-
cupant at very little weight cost,’ will incorpo-
rate pelvic ischial tuberosity pressure-point sup-
port, and will include the features of the new
BOAC delethaitized seat®).

9. Seat-belt—shoulder-strap restraint system.

10. “Bird-proof” nondistortion, double-layer
windows, providing low interior sound level and
wide vision.

11. Rollover cabin-strueture cupability.

Subsequent to the completion of the mockup
and following possible additional or revised con-
cepts in its construction, it is anticipated that a
prototype cockpit will be constructed within an
actual airframe, and high-speed impact tests with
anthropomorphic dummies and accelerometers
undertaken.

The results of these tests will then be avail-
able to all manufacturers who may incorporate
proven crash-safety features in their future air-
craft, A marked decrease in the morbidity and
mortality of aircraft accidents is anticipated.

Actually, in many present aircraft, the buildup
of high forces during impacts is an obvious oc-
currence, since, for specific bones, specific maxi-
mmm forces are required to produce fractures.
For example, the lower tibia requires about 1,000
pounds of force applied normal to its long axis
to result in a fracture? Other bones have their
own fail points, and one can almost calibrate the
forces that accurred within the cockpit of a
crashed aircraft from a study of which bones are
fractured in what places.

Vv. Summary.

Three principles for accomplishing a high de-
lethalization quotient within the cockpit are
given and discussed.

Spedific examples of existing crash-safety-
design features are presented.

Finally, a description of the delethalized CARI
cockpit is provided with accompanying comments
relevant to future aircraft design.



AM 66-3

COCKPIT DESIGN FOR IMPACT SURVIVAL

S. R. Mohler, M.D.
J. J. Swearingen, M.S.

Approved by Released by

> e
Yillit Ste wo
J. R. Doze, M.D. P. V. Sreczt, M.D.

Cur, Civ, Azromepica, InstrTuTe Ferran Air SuRGEON

February 1966

FEDERAL AVIATION AGENCY

Office of Aviation Medicine
Civil Aeromedical Research Institute
Oklahoma City, Oklahoma



factor determined by the prescribed peak of g
forces, which is anticipated to be the point at
which additional rising forces will be traded into
the next layer, the subcutaneous layer. This
factor is determined by the viscoelastic property
of skin that results in a buildup of resistance to
deformation from sudden rapidly applied de-
celerations.

‘Similarly, the next underlying layer of the
structure bears a physical equivalency to the sub-
cutaneous tissue, and the third structural layer is
matched with the facial muscles:

‘These various layers may be made of different
substances, including Ensolite, Stafoam, honey-
comb aluminum, foamed aluminum, honeycomb
nonmetallic materials, or other substances that
deform to pressure but “recoil” as is the case with
rubber.

The fourth layer matches the skull in strength,
and provides the basic support in bringing the
head to a stop within a sublethal deceleration-
time profile.

This fourth layer may be constructed of a
malleable material, including such substances as
sheet aluminum. Behind the fourth layer is a
filler material capable of being rapidly displaced
during impacts to spread the impact forces over
the greatest possible “interface” area.

IV. Feasibility.

Is it technologically and economically feasible
to produce aircraft, with further delethalized in-
teriors?

Examples of partial compliance with Princi-
ples Ono and Two can be found in almost all
production aircraft, present and past, civil and
military. Many desirable features are incorpo-
rated in U.S. Army light aircraft.

Almost every specific recommendation within
the context of these first two principles can be
found utilized in one or another production air-
craft, illustrating the feasibility of these prin-
ciples,

In other words, Principles One and Two can
be immediately implemented to increasing ex-
tents and can begin to appear more extensively
in forthcoming aircraft. Our approach is pro-
Spective, therefore.

Implementing Principle ‘Three will take a bit
more time. The design engineer needs mathe-
matical quantities. He needs to know the toler-

ances of vairous pontions of the human body to
impacts of various magnitudes and durations.
CARI is preparing this data, a certain portion
of which comes from the automobile-accident ex-
perience. Also, the appropriate materials must
exist, be economically within reach, and be amen-
able to production techniques.

Lastly, the spirit must exist in both the seller
and the buyer to “get on with the job of crash
safety in an aggressive fashion.”

Figure 10 illustrates an hypothetical light-air-
plane cockpit incorporating aspects of all three
principles. A mockup is now being constructed
at CARI in the interest of demonstrating in a
tangible fashion various means of delethalizing
the cockpit. The chief worker on this mockup
is Mr. A. Howard Hasbrook, who coined the
word delethalization in 1951.

Ficure 10,

The following are among the features con-
tained in the CARI cockpit :

1. Noninjurious broad-surface wheel (with
back-side grooving), possibly of transparent ma-
terial.

2. Side-hinged push-pull rod, longitudinally
telescoping, with impact “band-away” feature.

3. Countersunk throttle and propeller controls,
countersunk attitude and gyro-heading-indicator
adjustors, and “press-button” piano-key flush
switches.

4. “Pop-back” instruments, surrounded by
“mirror-image” sandwich material.


just above the pilot’s head, with their sharp end
pointed toward his cranium. The use of flat
center-pivot push switches represents “delethaliz-
ation” of this problem.

Gyro-heading-indicator adjustment knobs, ra-
dio equipment knobs, and other controls, often
are positioned so that they inflict puncture
wounds on the face during inpacts. Counter-
sunk control knobs solve this situation.

Drs. Gikas and Huelke report that one auto-
mobile-accident victim received fatal injuries
when an instrument panel knob penetrated his
calvarium and entered the frontal lobe of the
brain.” They illustrate the case with a post-
mortem roentgenogram. Aircraft pilots are not
immune to such occurrences.

‘Puncture wounds can make serious or fatal in-
juries. The elimination of objects within the
cockpit that can produce puncture wounds repre-
sents the first of three principles of delethaliza-
tion.

First Principle: Delineate the envelope of mo-

tion of the occupants in a given location and re-:

move from this envelope, or properly modify the
design thereof, all sharp, elongated, brittle,
pointed, or similarly shaped objects.

delethalization

\

Fieure 2,

Figure 2 shows the superimposed profiles of
various civil aircraft.1? To this is added the en-
velope of motion of a pilot’s head and extremi-
ties. Since it is impossible to conceive of re-
moving the parts of the cockpit that may collide
with the pilot during impacts, a combination of

delethalization principles and proper restraint-
system design appears desirable.

A restraint system alone is not the complete
answer to occupant protection, since, although
the system may keep the ocoupant from going to
the instrument panel during impacts, it does not
keep the panel from going to the occupant. The
restraint system is important, however, and it is
herein listed as the second principle.

Second Principle: Employ a body restraint
system, consisting of a belt and a shoulder har-
ness, capable of withstanding 25 g’s.1°

This system can utilize a single-strap fixed
chest strap or an inertial-reel single strap. All
recent Meyers light aircraft are routinely fitted
with the single-strap shoulder-harness-lap belt
combination, a distinct contribution to air safety.
A lightweight inertial-reel shoulder harness by
Pacific Scientific of Los Angeles is currently
being tested by CARI. Interestingly, the Sikor-
sky S-88A, issued a Type Certificate in 1998
(ATC #60), contained one of the best passenger
seat belts ever used (at least four times as wide
‘as present belts, thus covering the center of
gravity of seated children).*

The 25-g capacity ensures that so long as the
fuselage remains intect (a good working defini-
tion of survivability), the restraint system will
hold (it follows that the seat should itself be
capable of staying in place under 25-g all-di-
rectional loads) .

It should be noted that many gliders, including
those manufactured by the Schweitzer Company,
have utilized shoulder harnesses to advantage.
Aerial-applicator aircraft have also, and the
Piper Pawnee illustrates how a good restraint-
system—smooth-panel combination, have been
put together? Among the other “new-genera-
tion” aerial-applicator craft with good safety
features are the Snow, Callair, and Ag-Cat.

Also, as Oolonel Stapp points out, the Air
Force policy of utilizing a 250-pound (attaired)
ocoupant, is ideal in determining seat strengths,
since this guarantees almost ‘all persons at least
25 g’s of tie-down protection.

A pilot (or an airline passenger) may be fig-
uratively seen (Figure 3) sitting in place, facing
two hazards: a sledgehammerlike hard structuré
directly ahead, flanked by various sharp objects.
All is well if'conditions remain static.


COCKPIT DESIGN FOR IMPACT SURVIVAL

I. Introduction.

The authors estimate that as many as half of
those now lost annually in survivable aircraft
accidents would survive should existing data on
tissue protection during impacts be incorporated
more extensively in aircraft design. The eco-
nomic and other benefits to the aviation com-
munity attending the return to flying of these
accident victims (aside from the humanistic as-
pects), makes it highly desirable that future air-
craft contain available bioengineering design ad-
vances.

If the interior of a typical light aircraft is
scrutinized, myriads of pointed and sharp-edged
protruberances are seen. Under static conditions,
these objects cause little problem, but, during im-
pact circumstances, they produce punctures,
creases, and fractures in the protoplasm pressed
against them. Pearson provides a broad analysis
of this matter.’

With some experience in accident investiga-
tion, one can almost “read” the make of aircraft
by viewing the “impact signature” left by the
respective aircraft on the occupants of specific
seats.

Considerable attention has been given to the
prevention of impact injury and death in ground
vehicular and aircraft accidents. * * 7° This as-
pect of preventive medicine can be improved, and
this paper will discuss possible approaches to ef-
fecting the further incorporation of cockpit-
design safety features.

II. Discussion.

The aircraft interior portrayed in Figure 1
represents a composite picture of the latent ca-
pacity of various existing layouts to maim or
kill pilots. For example, circuit breakers or
toggle switches line the lower portion of the
instrument panel, somewhat similar in appear-
ance to teeth and capable of inflicting toothlike
injuries.

Frevne 1.

Also, the rudder pedals and associated struc-
tures, as often constructed at present, are con-
ducive to serious injury during their entangle-
ments with the lower legs subsequent to impacts.

Additionally, pilots may be found on occasion
impaled upon a portion of the control wheel, as
on the horns of a bull, especially in cases where
the wheel is constructed of brittle material. In
configurations where a wheel of the type illus-
trated is installed with the points facing the
floor of the plane, the hazard to the lower trunk
and thighs is obvious.

The location of the magnetic compass near the
pilot’s forehead is especially poor with respect to
impact injury. The Piper Cherokee has good
magnetic-compass location, within the instrument
panel proper.

The installation of the trim-tab controls in a
location not likely to injure parts of the body
during impacts is an important consideration.
The Cessna 150-172-182 series illustrates a de-
sirable location for. these controls, which are
found on the floor bebween the two front seats.

Dome-light switches may be located at times



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