Effect of Passenger Position 

on Crash Injury Risk in 

Transport-Category Aircraft

Amanda M. Taylor

Richard L. DeWeese

David M. Moorcroft

Civil Aerospace Medical Institute

Federal Aviation Administration

Oklahoma City, OK 73125

September 2015

Final Report

DOT/FAA/AM-15/17

Office of Aerospace Medicine

Washington, DC 20591

Revised 11/19/2015

(see erratum page, 

inside cover)
NOTICE

This document is disseminated under the sponsorship 

of the U.S. Department of Transportation in the interest 

of information exchange. The United States Government 

assumes no liability for the contents thereof.

___________

This publication and all Office of Aerospace Medicine 

technical reports are available in full-text from the 

Federal Aviation Administration website.

ERRATA

This report, as originally published, contained errors, all of which have been corrected and eliminated from 

the revised report. The authors regret the oversight. Below is a list of corrections.

1. In the original version of this report, Tables 3,4,5,and 6 contained a typographical error. The Criteria Limit for 

the Negative Right Femur My (in-lb) and the Negative Left Femur My (in-lb) should have been 2655, not 2265.

2. Page A1: Third bullet, last sentence, change “exceeded the limit” to “was relatively high.”

3. Page A2: Third bullet, last sentence, change “exceeded the limit” to “was relatively high.”

4. Page A3: Third bullet, second sentence, change “exceeded the limit” to “was relatively high.”

5. Page A6: Third bullet, last sentence, change “which exceeded the limit” to “that was relatively high.”

6. Page A7: Third bullet, last sentence, change “both of which were greater than the limit” ” to “The TI exceeded 

the limit and the Y-Axis moment was relatively high.”

7. Page A8: Third bullet, next to last sentence, change “which exceeded the limit” to “that was relatively high.”

8. Page A9: Third bullet, 4th sentence, change “Y-Axis” to “positive Y-Axis” and change “above the limit” to “relatively high.”

9. Page A10: Third bullet, next to last sentence, change “exceeded the limit” to “was relatively high.”

10. Page A11: Third bullet, last sentence, change “exceeded the limit” to “was relatively high.”

11. Page A13: Third bullet, last sentence, change “below the criteria limit” to “relatively low.”

12. Page A14: Third bullet, last sentence, change “below the limit” to “relatively low.”

13. Page A15: Third bullet, last sentence, change “below the criteria limit” to “relatively low.”

14. Page A16: Third bullet, last sentence, change “well below the criteria limit” to “relatively low.”

15. Page A17: Third bullet, last sentence, change “well below the limit” to “relatively low.”
i

Technical Report Documentation Page

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

DOT/FAA/AM-15/17

4. Title and Subtitle 5. Report Date

Effect of Passenger Position on Crash Injury Risk in 

Transport-Category Aircraft

September 2015

6. Performing Organization Code

7. Author(s) 8. Performing Organization Report No.

Taylor AM, DeWeese RL, Moorcroft DM

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)

FAA Civil Aerospace Medical Institute

P.O. Box 25082 11. Contract or Grant No.

Oklahoma City, OK 73125

12. Sponsoring Agency name and Address 13. Type of Report and Period Covered

Office of Aerospace Medicine

Federal Aviation Administration

800 Independence Ave., S.W.

Washington, DC 20591 14. Sponsoring Agency Code

15. Supplemental Notes

This work is to support the Fire & Cabin Safety Technical Community Representative Group Project: 

Prevention of Injuries That Impeded Egress, Project 2011-05/2012-06. 16. Abstract

In the event of an accident, one action that an occupant can take to contribute to their survival is to 

assume an appropriate “brace-for-impact” position. This is an action in which a person pre-positions their 

body against whatever they are most likely to be thrown against, significantly reducing injuries sustained.

Occupants in the US Airways flight 1549 sustained shoulder injuries that they attributed to the brace 

position; therefore, the NTSB recommended that the position be re-evaluated.

The Federal Aviation Administration investigated this by conducting a series of 17 sled impact tests, 15 

with two rows of transport category forward facing passenger seats and two with a bulkhead configured to 

represent the types of seats currently in use. Head, neck, upper and lower leg injury risks were evaluated 

using an advanced test dummy and injury criteria from current FAA regulations, Federal Motor Vehicle 

Safety Standards, European auto safety regulations, and applicable research findings.

The current brace position, head against the seat back with hands on top of the seat back, was only 

successful in reducing head injury risk for locked-out seat backs. However, for full break-over and energy 

absorbing seat backs, this position increased the severity of the head impact. There was, however, no 

evidence that the anthropomorphic test device interaction with any of the seatback types resulted in hyperextension of the shoulder joint. Significant lower leg injury potential was not observed in this study, and 

therefore adopting lower leg injury criteria at this time does not appear to be a benefit. Even in the worst 

case test condition, the femur axial compressive force was below the regulatory limit, indicating that the 

femur compression criteria currently cited in FAA regulations is not likely to be exceeded in passenger seat 

dynamic qualification tests. To reduce detrimental interaction between the occupant’s arms and the 

seatback, the current position was modified by placing the hands down by the lower legs instead of on the 

seat back. This alternate position was successful in significantly reducing head and neck injury risk for all 

of the seat back types evaluated. This research has led to the determination that as seat technology has 

evolved, the most effective brace position has as well, and the current positions recommended in AC 121-

24B may need some adjustment to provide an equivalent level of safety for all passenger seat back types.

17. Key Words 18. Distribution Statement

Brace for Impact, Passenger Position, Leg Injury 

Criteria, Neck Injury Criteria, Head Injury Criteria, 

Femur Compression, Femur Bending

Document is available to the public 

through the Internet:

www.faa.gov/go/oamtechreports

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price

Unclassified Unclassified 42

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

iii

ACKNOWLEDGMENTS

This work is to support the Fire & Cabin Safety Technical Community Representative Group Project: Prevention 

of Injuries That Impeded Egress, Project 2011-05/2012-06. Without the full support of the CAMI technical 

staff—Jim Biegler, David DeSelms, and Ronnie Minnick—we would not have been able to complete the work. 

v

Contents

Effect of Passenger Position on Crash Injury 

Risk in Transport-Category Aircraft

Background. 

Methods. 

Test Device  

Impact Surfaces  

Seat Pitch. 

Instrumentation. 

Seating Procedures. 

Restraints. 

Data Analysis. 

Test Matrix. .

Results. .

Locked-Out Seat Back  .

Full Break-Over Seat Back. .

Energy Absorbing Break-Over Seat Back  .

Bulkhead  .

Discussion. .

Injury Risk Evaluation. .

Neck Injury  .

Brace Position Evaluation. .

Limitations. .

Effect of Combined Loading  .

Seat Back Range of Stiffness. .

Seat Back Distribution. .

Test Repeatability. .

Conclusions. .

References. .

Appendix A. Test Analysis. 

1

Effect of Passenger Position on Crash I

Risk in Transport-Category Ai

BACKGROUND

It is a common misconception that if an airplane crashes, all 

occupants will likely perish. While in reality, according to the 

National Transportation Safety Board (NTSB), from 1983 to 

2000, 96% of occupants survived [1]. One action that occupants 

can take to contribute to their survival is to assume an appropriate “brace for impact” position. Descriptions of this type of 

position have been in passenger briefings for decades. The goal 

is to reduce the risk of injuries from a secondary impact, with 

the primary impact being between the airplane and the ground, 

and the secondary impact being between the occupants and the 

inside of the airplane. “Brace for impact” is an action in which 

occupants pre-positions their body against whatever they are 

most likely to impact, and thereby significantly reducing impact 

forces and the resulting injuries. 

While the positive benefits of bracing seem somewhat obvious, public interest in the purpose and effectiveness of the brace 

position persists. The position that will protect the maximum 

range of occupants has long been one of the most frequently 

asked questions of crash safety researchers [2]. During the 1980s, 

brace position effectiveness was investigated using the then-new 

dynamic impact test techniques and the recommendations were 

adjusted to reflect the findings. By the late 1980s, the effort to 

develop crashworthy seats resulted in a large amount of data 

concerning the flail response of occupants seated in a variety of 

configurations. These data were used to develop specific brace 

recommendations for many potential seating configurations [3]. 

Many of these recommendations formed the basis of the brace 

positions cited in Advisory Circular (AC) 121-24B Appendix 

4 (Fig.1). Subsequent crash investigations have resulted in new 

recommendations concerning brace positions [4]. These new 

recommendations, as well as Federal Aviation Administration 

(FAA) guidance and previous research findings, were used as the 

basis of the brace recommendations contained in SAE Aerospace 

Recommended Practice 4771 [5].

On January 15, 2009, US Airways flight 1549, an Airbus 

A320, ditched in the Hudson River approximately 8.5 miles 

from LaGuardia Airport. Four passengers sustained serious 

injuries attributed directly to the impact; two passengers 

sustained similar shoulder injuries. Both described assuming 

similar “brace for impact” positions in which they placed their 

arms on the seat back in front of them and leaned over placing 

their head on the back of their hands. This is a similar position 

to the one depicted in the US Airways safety card (Fig. 2). 

As a result of this accident, the NTSB issued several safety 

recommendations to the FAA, one of which stated, “Conduct 

research to determine the most beneficial passenger brace 

position in airplanes with non-break over seats installed. If 

the research deems it necessary, issue new guidance material 

on passenger brace positions” [6]. Injuries sustained by occupants, passenger confusion as to the proper brace position, 

and newer technology used in seats brought to the forefront 

a need to review brace position effectiveness to determine 

if the recommended positions were still appropriate for the 

widest range of occupants. Some recent research data were 

available but did not specifically address the effect of the seat 

back folding over [7]. 

While complying with the NTSB call to evaluate the “most 

beneficial passenger brace position in airplanes with non-break 

over seats installed,” the Civil Aerospace Medical Institute 

(CAMI) completed a more thorough project that evaluated 

passenger brace position for the three most common types of 

seat-hinge mechanisms: locked-out (also known as non-break 

over), full break-over, and energy absorbing break-over. This 

evaluation included a comprehensive assessment of occupant 

injury risk, comprising current regulatory criteria and additional 

criteria that may be informative, and also is a component of a 

FAA Aviation Safety research task to study injuries that could 

impede egress after a crash. Head and leg injuries are considered 

to have the greatest effect on the ability to self-evacuate, and 

we decided to evaluate leg injury risks simultaneously with the 

brace position research, since the necessary test configurations 

were similar for both projects.

Figure 1. Passenger Brace Positions in 

AC 121-24B

Figure 2. Passenger Brace Position Shown in the US Airways Safety 

Information Card
2

METHODS

We investigated brace positions by conducting a series of sled 

impact tests with two rows of forward-facing passenger seats, 

and a bulkhead wall configured to represent the types of seats 

in use. The factors investigated were: seat back type, occupant 

position (braced and un-braced), the spacing between rows, occupant stature, and interaction with interior walls. Leg injury 

risk was investigated during the same series of tests. The factors 

investigated were leg initial position, the spacing between rows, 

occupant stature, contact surface stiffness, and interaction with 

the floor. Seventeen tests were completed using the deceleration sled at CAMI with the 16 G, 44 feet per second impact 

severity defined in the Code of Federal Regulations (CFR) 14 

CFR Part 25.562. Figure 3 shows a typical deceleration pulse 

for this series. To reduce test-to-test variability and enable direct 

comparison, no yaw or floor deformation was included in the 

experimental design. 

Test Device 

The Anthropomorphic Test Device (ATD) used to assess 

injury was a fiftieth percentile male FAA Hybrid III. This ATD 

differs from the standard Hybrid III used in automotive testing because it has been modified to better emulate the more 

upright posture of an occupant in an airliner seat and provide 

kinematic and vertical response equivalent to the Hybrid II [8]. 

The Hybrid II or an equivalent (such as the FAA Hybrid III) is 

currently required for certification tests of aviation seats. The 

modification consists of several Hybrid II parts substituted into 

the structure, including the lumbar spine, abdominal insert, 

chest jacket, and upper leg bone (Fig. 4). 

The FAA Hybrid III ATD was selected in part because of 

its capability to measure neck and lower leg loads. This ATD 

used for the study had load cells at both the upper and lower 

neck positions and instrumented lower legs installed. The instrumented lower legs have two 5-axis load cells, one in the 

upper and one in the lower part of the tibia, which records 

forces and moments. 

Impact Surfaces 

Three types of seat backs, in addition to a rigid wall and knee 

plate, were chosen for evaluation:

Locked-out seat back 

A locked-out seat back, also referred to as non-break over, has 

a simple nut-and-bolt connection in the linkage that connects 

the seat back to the seat frame. When loaded by inertial forces 

or when struck from behind, the amount of forward flexion of 

the seat back is dependent on the strength and stiffness of the 

seat back structure only, as the nut-and-bolt connection does 

not permit rotation of the seat back frame. Significant loading 

by an occupant of the row behind usually results in some initial 

forward motion due to elastic deformation, followed by permanent deformation to the seat back structure. Seat backs of this 

type are primarily found in aircraft that are not required to meet 

the head impact protection requirements of § 25.562 (c) [9].

Full break-over seat back

A full break-over seat back is free to fold over about its hinge 

point, limited only by friction in the hinge joint and contact 

with the seat bottom or occupant of the seat. All passenger seat 

backs must resist folding when a force up to 25 lb is applied at 

the top of the seat back, as defined in AC 25-17A section 25.785 

81.b paragraph d [10]. This is necessary so that seat backs can 

provide an effective hand-hold for passengers walking down the 

aisle. This resistance is typically provided by an adjustable friction mechanism in the hinge joint. To ensure consistent folding 

force during these tests, a shear pin was installed in the hinge 

linkage in lieu of a friction device. The pin was sized to shear 

when the force at the top of the seat back exceed 35 lb. This 

force accounts for in-service adjustment tolerance on the 25 lb 

minimum force. This type of seat back was common on older 

seat designs that are being replaced by newer ones and would 

only be found in aircraft that are not required to meet the head 

impact protection requirements of § 25.562 (c) [9]. 

Figure 3 – Typical Sled Deceleration Pulse

Figure 4. FAA Hybrid III, Orange-Outlined Parts are Hybrid II
3

Energy absorbing (EA) break-over seat back 

An energy-absorbing break-over seat back is designed so that 

when the aft surface of the seat back is struck by the occupant 

behind it, the surface moves forward at a rate that limits the 

magnitude and duration of the occupant’s head acceleration. 

This controlled motion is usually provided by a combination 

of local deformation of the seat back surface and overall stiffness provided by the folding action of the seat back about the 

hinge at its base. The local stiffness of the back depends on its 

construction (i.e., video screen, tray table, literature pocket) 

and can vary significantly. The overall stiffness of the seat back 

depends on the folding resistance of the hinge mechanism and 

the height of the impact point above the hinge. In general, the 

closer the impact point is to the hinge, the greater the overall 

stiffness due to the decreased leverage. The controlled motion 

provides head impact protection for occupants of transport 

category passenger seats equipped with lap belts.

The EA seat back used for this study controlled its forwardfolding with a combination of friction washers and dual shear 

pins in the hinge mechanism. The shear pins are sized to limit 

the contact force produced when the head of the occupant strikes 

the seat back from behind. This allows the seat to absorb some 

of the occupant’s energy prior to folding over. In this case, each 

pin would shear sequentially when a force of approximately 

220 lb was applied horizontally at the top of the tray table, 19 

in above the hinge point. During a crash, the first bolt shears 

due to inertial forces acting on the seat back. The second bolt 

then shears when the occupant comes into contact with the 

seat back. The resisting force provided by this energy-absorbing 

mechanism is considered typical for seat backs designed to limit 

head injury potential [11]. 

The seat back friction washers were adjusted to provide 35 lb 

of resistance to a force applied at the top of the seat tray table. 

This force corresponds to the maximum applied force permitted 

when retuning a seat back upright for evacuation clearance evaluation after a dynamic test, as stated in SAE Aerospace Standard 

(AS) 8049b paragraph 3.5.5 [12]. In-service seats are similarly 

adjusted to ensure compliance with this requirement. Once the 

friction washers were adjusted, the shear pins were installed into 

the hinge mechanism to complete the setup. This dual shear type 

of energy absorber has a stiffness that falls between the break-over 

seat back and locked-out seat back. 

Seats utilizing EA seat backs are typically found in aircraft 

designed since 1988 that must meet 14 CFR 25.562, although 

they can be installed as replacements in other aircraft as well. 

Since FAA regulations require that seats meeting § 25.562 be 

installed in all newly manufactured transport aircraft operated 

in passenger carrying operations after October 27, 2009, EA seat 

backs will eventually be the prevalent seat back type in service 

as newer aircraft are added to the fleet.

Bulkhead 

To evaluate a worst case axial neck loading, a nearly rigid wall 

was constructed to emulate a seat just aft of a bulkhead. The wall 

consisted of a 1-in thick fiberglass faced Nomex® honeycomb 

core panel of the type used in typical aircraft interior walls, 

which was rigidly supported by a 0.5-in aluminum plate (Fig. 5). 

Solid knee plate 

To determine the likely maximum worst case axial loading 

into the femur, a rigid plate was attached to the seat frame where 

the knee would contact (Fig. 6).

ATD positions 

The ATD position was varied to assess the different injury 

risks for each scenario. Some of the tested positions were intended to emulate the currently recommended brace positions. 

Figure 5. Rigid Wall with Honeycomb Panel

Figure 6. Knee Plate
4

However, the actual positions varied somewhat from the guidance illustrations due to limitations of the ATD construction 

and articulation capability. For this study, the positions tested 

are defined in terms of torso, hand, and leg positions.

Torso positions

•	 Upright: The nominal seated position. This position is used 

for qualification tests.

•	 Braced: Leaned forward with the head touching the seat 

back. A cord over the back was necessary to maintain this 

initial position.

•	 Pike: Leaned all the way over until the neck was horizontal 

and the chest was touching the tops of the thighs. (Fig. 7) 

This position was used to assess the worst case axial loading 

in to the neck. To achieve this position, it was necessary to 

remove the abdominal insert from the ATD and hold the 

torso down with a frangible string over the back (designed 

to break immediately after the test began).

Hand positions

•	 Top of thighs: the nominal position used for qualification tests 

•	 Top of seat back: resting on seatback, taped lightly in place

•	 Back of head: hands placed on head and taped together to 

stay in position 

•	 Side of legs: arms straight with hands just below knees

Leg positions

•	 Vertical: the nominal position used for qualification tests 

(Fig. 8)

•	 Forward: the feet placed as far forward as possible while 

remaining flat on the floor (Fig. 9) 

•	 Aft: feet placed as far back as possible, but limited by contact 

with the baggage bar (Fig. 10) This position has been previously proposed as a means to reduce leg injury [4]

•	 Unsupported: no floor installed at that seat place. Intended 

to simulate a short stature occupant whose legs do not touch 

the floor, and thus will swing forward unimpeded from an 

initial vertical position (Fig. 11)

Figure 7. Pike Position Behind a Rigid Wall

Figure 8. Lower Leg “Vertical” Position

Figure 11. Unsupported Leg Position (No Floor)

Figure 10. Lower Leg “Aft” Position

Figure 9. Lower Leg “Forward” Position
5

Seat Pitch

The seat pitch used for most of the tests was about 30.5 in, 

which reflects one of the narrowest pitches currently used by 

major US air carriers (Fig. 12). This was chosen as a near worst 

case for evaluating brace effectiveness, since at close pitch, a 

braced occupant would initially be more upright than at a longer 

pitch. This more upright position would allow occupants more 

space to generate differential velocity between their head and 

the seat back, resulting in higher injury risk. This close pitch 

was also considered worst case for leg impact since the chance 

of leg interaction with the seat in front was greater. Longer 

pitches were used to investigate specific leg and head injury 

risks. A wall was used for two tests and was placed at 35 in from 

the Seat Reference Point (SRP) of the launch seat (Fig. 13). 

Thirty-five in was chosen because that position is just beyond 

the nominal head strike zone defined in AC 25-17A section 

25.785 81.b paragraph d [10] and is therefore a commonly 

used installation dimension. 

Instrumentation

Electronic instrumentation 

ATDs were instrumented as shown in Tables 1a-c. For this 

project, lower leg injury potential was measured with two 

Denton-type lower legs recording both upper and lower tibia 

forces and moments. The tensions on both sides of the lap belt 

were measured between the pelvis of the ATD and the belt anchor with webbing transducers. The forces applied to the floor 

attachments of the target seat were also measured using 3-axis 

10,000 lb load cells. The test data were gathered and filtered per 

the requirements of SAE J211/1 [13]. The sign convention of 

the recorded signals conformed to SAE J1733 [14].

Video coverage 

High-speed (1,000 frames per second), high-resolution (1024 

x 512 pixels) color video was captured from both side directions 

by Phantom cameras (Vision Research), aimed perpendicular 

to the sled travel. Rigidly mounted targets were affixed to the 

ATD’s knee and ankle with the center of the target representing the center of the joint to facilitate motion analysis. Targets 

were also placed on the hip point, head center of gravity, seat 

cross-tubes, and seat backs. The position and velocity of selected 

targeted points were derived from the videos using procedures 

complying with the requirements of SAE J211/2 [15]. 

Figure 12. Seat to Seat Configuration

Figure 13. Seat to Wall Configuration
6

Table 1a. Instrumentation Summary

Ch. 

Num Description

Filter 

Class Range Units Rack

1 Sled X Acceleration 60 25 G 1

2 Left Belt Strap 60 3000 lb 1

3 Head Ax 1000 2000 G 1

4 Head Ay 1000 2000 G 1

5 Head Az 1000 2000 G 1

6 Head Rx ARS18K 180 18000 Deg/Sec 1

7 Head Ry ARS18K 180 18000 Deg/Sec 1

8 Head Rz ARS18K 180 18000 Deg/Sec 1

9 Upper Neck Fx 600 2000 lb 1

10 Upper Neck Fy 600 2000 lb 1

11 Upper Neck Fz 600 3000 lb 1

12 Upper Neck Mx 600 2500 in-lb 1

13 Upper Neck My 600 2500 in-lb 1

14 Upper Neck Mz 600 2500 in-lb 1

15 Lower Neck Fx 600 3000 lb 1

16 Lower Neck Fy 600 3000 lb 1

17 Lower Neck Fz 600 3000 lb 1

18 Lower Neck Mx 600 4000 in-lb 1

19 Lower Neck My 600 4000 in-lb 1

20 Lower Neck Mz 600 4000 in-lb 1

21 Thorax Ax 600 2000 G 1

22 Thorax Ay 600 2000 G 1

23 Thorax Az 600 2000 G 1

24 Thorax Rx ARS12K 180 12000 Deg/Sec 1

25 Thorax Ry ARS12K 180 12000 Deg/Sec 1

26 Thorax Rz ARS12K 180 12000 Deg/Sec 1

27 Thoracic Fx 600 3000 lb 1

28 Thoracic Fy 600 3000 lb 1

29 Thoracic Fz 600 4500 lb 1

30 Thoracic Mx 600 5000 in-lb 1
7

Table 1b. Instrumentation Summary (continued)

Ch. 

Num Description

Filter 

Class Range Units Rack

31 Thoracic My 600 8000 in-lb 1

32 Pelvis Ax 600 500 G 1

33 Pelvis Ay 600 500 G 1

34 Pelvis Az 600 500 G 1

35 Pelvis Rx ARS12K 180 12000 Deg/Sec 1

36 Pelvis Ry ARS12K 180 12000 Deg/Sec 1

37 Pelvis Rz ARS12K 180 12000 Deg/Sec 1

38 Lumbar Fx 600 3000 lb 1

39 Lumbar Fy 600 3000 lb 1

40 Lumbar Fz 600 5000 lb 1

41 Lumbar Mx 600 10000 in-lb 1

42 Lumbar My 600 10000 in-lb 1

43 Lumbar Mz 600 4000 in-lb 1

44 Right Femur Fx 600 3000 lb 1

45 Right Femur Fy 600 3000 lb 1

46 Right Femur Fz 600 5000 lb 1

47 Right Femur Mx 600 3000 in-lb 1

48 Right Femur My 600 3000 in-lb 1

49 Right Femur Mz 600 4000 in-lb 1

50 Right Upper Tibia Fx 600 2500.1 lb 1

51 Right Upper Tibia Fy 600 2500.1 lb 1

52 Right Upper Tibia Fz 600 2500.1 lb 1

53 Right Upper Tibia Mx 600 3500.5 in-lb 1

54 Right Upper Tibia My 600 3500.5 in-lb 1

55 Right Lower Tibia Fx 600 2500.1 lb 1

56 Right Lower Tibia Fy 600 2500.1 lb 1

57 Right Lower Tibia Fz 600 2500.1 lb 1

58 Right Lower Tibia Mx 600 2500.1 in-lb 1

59 Right Lower Tibia My 600 2500.1 in-lb 1

60 Right Knee String Pot 180 1.417323 in 1
8

Table 1c. Instrumentation Summary (continued)

Ch. 

Num Description

Filter 

Class Range Units Rack

61 Left Femur Fz 600 5000 lb 1

62 Left Femur My 600 3000 lb 1

63 Left Knee String Pot 180 1.417323 in 1

64 Right Belt Strap 60 3000 lb 1

65 Sled X Accelerometer 60 25 G 2

66 Front Left Floor Load Cell Fx 60 10000 lb 2

67 Front Left Floor Load Cell Fy 60 10000 lb 2

68 Front Left Floor Load Cell Fz 60 10000 lb 2

69 Front Right Floor Load Cell Fx 60 10000 lb 2

70 Front Right Floor Load Cell Fy 60 10000 lb 2

71 Front Right Floor Load Cell Fz 60 10000 lb 2

72 Rear Left Floor Load Cell Fx 60 10000 lb 2

73 Rear Left Floor Load Cell Fy 60 10000 lb 2

74 Rear Left Floor Load Cell Fz 60 10000 lb 2

75 Rear Right Floor Load Cell Fx 60 10000 lb 2

76 Rear Right Floor Load Cell Fy 60 10000 lb 2

77 Rear Right Floor Load Cell Fz 60 10000 lb 2

78 Left Leg Upper Tibia Fx 600 2500 lb 2

79 Left Leg Upper Tibia Fy 600 2500 lb 2

80 Left Leg Upper Tibia Fz 600 2500 lb 2

81 Left Leg Upper Tibia Mx 600 3500 in-lb 2

82 Left Leg Upper Tibia My 600 3500 in-lb 2

83 Left Leg Lower Tibia Fx 600 2500 lb 2

84 Left Leg Lower Tibia Fy 600 2500 lb 2

85 Left Leg Lower Tibia Fz 600 2500 lb 2

86 Left Leg Lower Tibia Mx 600 2500 in-lb 2

87 Left Leg Lower Tibia My 600 2500 in-lb 2

88 Left Leg Knee Clevis Left 600 2000 lb 2

89 Left Leg Knee Clevis Right 600 2000 lb 2

90 Right Leg Knee Clevis Left 600 2000 lb 2

91 Right Leg Knee Clevis Right 600 2000 lb 2
9

Seating Procedures

For this study, the ATD was seated in accordance with a 

procedure developed at CAMI that results in a consistent fore/

aft position and initial pelvis angle [29]. This procedure involves 

suspending the ATD above the seat cushion just enough to insert a flat hand (approximately 1 in) between the bottom of the 

pelvis and the cushion. A bar is then inserted under the thighs 

just aft of the knees and used to elevate them slightly so as not 

to interfere with the ATD self-aligning (Fig. 14). A force gage 

is used to press on the sternum of the ATD with approximately 

20 lb of force while the ATD is lowered into full contact with 

the seating surface. The ATD is rocked from side-to-side to fully 

settle it into the seat. Once seated, the lap belt was tightened 

“two finger tight,” as specified in SAE AS 8049b [12]. 

To generate the brace and pike positions, the initial seating 

procedure was the same as the upright position; however, once 

the ATD was seated and its lap belt tightened, the ATD was 

bent over into position and parachute chord was utilized to hold 

its torso in place. The parachute chord was routed to become 

slack immediately upon occupant forward motion so as not to 

interfere with ATD kinematics or loading. The pike position 

required removal of the abdominal insert to allow full bending 

at the lumbar spine. Two strands of frangible string were used 

to hold the torso in the pike position. 

After the ATD was positioned, a three-dimensional portable 

measuring arm was used to take multiple points on the sled, 

seat, and ATD. The sled points included the center of the seat 

tubes, belt anchor location, and seat back location. The ATD 

anatomical points included the hip point, head center of gravity, 

knee joint, and ankle joint. The angle of the leg, with respect to 

the vertical, was calculated from the measured location of the 

knee and ankle targets; the angle of the torso, with respect to 

the vertical, was calculated from the measured location of the 

head center of gravity and hip point targets. 

Restraints

Sixteen of the 17 tests used a conventional 2-point nylon lap 

belt, and one test used a polyester Y-belt. A Y-belt is a type of 

lap belt that has two attachment hooks on each end. These belts 

typically attach to a pair of anchor points on each side of the occupant, one at the conventional location and another at a higher 

point. This type of belt provides a more horizontal restraint path 

than a conventional belt to reduce forward excursion.

Data Analysis

Some injury criteria such as Head Injury Criteria (HIC), 

Normalized Neck Injury Criterion (Nij), and Tibia Index (TI) 

are derived from test data mathematical calculations. Instructions for calculating them can be found in the regulations that 

cite the criteria and in a useful summary report published by 

the Data Processing Vehicle Safety Workgroup [16].

Head Injury Criteria (HIC) 

HIC is used to evaluate head injury risk and has a pass/fail 

limit of 1,000; this corresponds to a 23%risk of an Abbreviated 

Injury Scale (AIS) AIS-3 or greater (serious) head injury or a 

47% risk of an AIS-2 or greater (moderate) head injury [17]. 

The AIS, developed by the Association for the Advancement 

of Automotive Medicine, provides a means of quantifying the 

severity (or threat to life) of a specific injury [18]. The HIC 

calculation cited in 14 CFR 25.562 differs from the automotive 

version in that the duration is unlimited but only includes the 

resultant head acceleration after head contact. Body-to-body 

contact is excluded from this calculation due to the undamped 

resonant response that can occur when relatively rigid parts of 

the ATD strike each other, which would give an artificially high 

HIC value. 

t

1

 is the initial integration time in seconds

t

2

 is the final integration time in seconds

a(t) is the total acceleration vs. time curve for the head in 

units of gravity

Note: The values of t1 and t2 are selected such that the HIC 

value is the maximum possible for the time period being evaluated.

Neck injury 

To limit the potential for neck injury in forward automotive 

crashes, 49 CFR 571.208 defines the criteria for neck tension 

and compression, as well as a criterion that combines the effect 

of the neck-bending moment and axial force, called Nij. This is 

Figure 14. Seating Procedure
10

not currently a pass/fail criterion in aviation, but a limit of 1.0 

is called for automotive testing [19]. The Nij calculation uses 

force and moment data measured with an upper neck load cell 

(projected to the occipital condyle location). The automotive 

compression limit is 899 lb and the tension limit is 937 lb [19].

Fz is the force at the transition from the head to neck

FZC is the critical force (1,530 lb)

MOCy is the total moment

Myc is the critical moment (1,200 in-lb)

Shoulder injury 

The FAA Hybrid III ATD does not have instrumentation 

to measure forces on the shoulder. Since the NTSB had identified shoulder injury as a potential risk for a braced occupant, a 

means of determining that injury risk was needed for this study. 

Hyper-extension of the shoulder joint in the sagittal (X-Z) plane 

was a possible injury mechanism for brace positions that place 

the hands on the seat back. To determine if it occurred during 

testing, the bolt securing the FAA Hybrid III’s shoulder rotation 

stop block was narrowed down to 0.133 inches to lower its shear 

strength to 660 lb (Fig. 15). This would allow the stop block to 

fail if the torque on the shoulder joint (in the x-z plane) exceeded 

990 in-lb. A post-test range of motion and visual inspection 

indicated whether the bolt had been sheared. This assessment 

was used to determine if there was potential for shoulder injury, 

but the torque required to shear the bolt has not been correlated 

to a specific injury severity. 

Upper leg injury 

The limit for axial compressive load in the femur is 2,250 

lb, per § 25.562, which represents a 15% risk of serious injury 

to the knee-thigh-hip complex [20]. In addition to axial loading, excessive bending moments can cause serious injuries. 

European regulations for protection of pedestrians cite a femur 

bending limit of 4,514 in-lb and a monitoring value of 2,655 

in-lb [21]. The 2,655 in-lb limit has been proposed by the 

European Enhanced Vehicle Safety Committee (EEVC) for 

pedestrian impacts and corresponds to a 20% risk of moderate 

injury to the femur [22]. Application of this criteria to other 

impact cases is limited because it was scaled using a dynamic 

multiplier against existing quasistatic femur-bending tolerance 

data, then scaled to the pedestrian leg form tester [23]. The 

pedestrian leg form is different than the femur used for the 

FAA Hybrid III in that the pedestrian leg form is designed to 

be used vertically to assess a car bumper’s interaction with a 

pedestrian. The FAA Hybrid III femur is designed to be used 

in a seated position to assess bending and axial loading in the 

upper leg. The two leg forms differ in their non-metallic parts 

and knee joint, as well. 

Appropriate application should also consider the loading case 

for which the limit was derived, specifically, a force applied perpendicularly to the femur mid-shaft, generating negative bending 

moments. In this study, this type of loading is produced when 

the lower legs are free to flail forward, and pelvis-forward rotation 

forces the femur down against the seat frame at approximately 

the femur mid-point. Alternately, if the lower legs do not flail 

and support the distal end of the femurs, forward flailing of the 

upper torso applies forces and moments to the ATD pelvis causing it to rotate forward and generate significant positive bending 

moments in the femur due to internal contact between the pelvis 

bone and femur. This means that the EEVC limit may be usful 

as a reference value for the load cases involving contact loading 

of the femur, but may not be valid for the other loading cases 

where ATD articulation creates the femur-bending moments.

Knee injury 

Tibia-Femur displacement is used as an indicator of knee 

injury risk in auto crashes. A limit of 0.6 in is cited in European 

regulations for protection of occupants in frontal collisions and 

corresponds to partial ligament failure in humans [21]. Significant 

displacement can occur when the tibia (rather than the patella) 

becomes the load path between the occupant and structure in 

a forward impact. 

Lower leg injury 

Lower leg injury potential is evaluated with the Tibia Index 

(TI), which combines the bending moments and axial forces in 

the lower leg. For each leg, one Tibia Index is calculated from 

the lower instrumentation and a separate TI is calculated from 

the upper instrumentation. European regulations for protection 

of occupants in frontal collisions call out a TI limit of 1.3, and 

a tibia compressive force limit of 1,800 lb [21]. According to 

Mertz, a TI reading less than 1.0 indicates that injury is unlikely 

[24]. To protect against tibia plateau fracture, he also proposed 

a supplemental compressive force limit of 1,800 lb in addition 

Figure 15. Shear Bolt for Shoulder Injury Evaluation
11

to the TI. Lower leg injuries are not current pass/fail criteria in 

aviation seat testing. 

Mx is the bending moment around the x-axis

My is the bending moment around the y-axis

(Mc)

R is the critical bending moment (1,991 in-lb)

Fz is the axial compression in the z-direction

(Fc)

Z is the critical compression force in z-direction (8,071 lb)

Test Matrix

Table 2 summarizes the variables evaluated for each test in this 

study. These include the seat pitch, seat back or impact surface 

type, belt type, ATD torso, hand, and leg positions, and whether 

a simulated floor was included.

RESULTS

Tables 3 through 6 summarize the test results grouped by impact 

surface type; the values shown in red exceeded the injury criteria. 

The top seven rows contain the details of the test condition, and 

the remaining rows contain the values for the injury criteria introduced in the Data Analysis section. A detailed evaluation of each 

test setup, including discussion, and video stills showing the initial 

condition and other times of interest, are provided in Appendix 

A. All tests met the pulse requirement defined in AC 25.562 [25].

Locked-Out Seat Back 

The locked-out seat back configuration was evaluated with 

six tests. Two tests with an unbraced occupant (A12037 and 

A12038) had HIC scores greater than 1,000, while a third test 

with an upright occupant (A13010) had a low HIC, but an Nij

value 50% higher than the limit due to an unusual interaction 

with the tray table. Conversely, the braced condition (A12036) 

produced a very low HIC, and Nij value less than half the limit. 

The leg injury criteria were generally favorable, although multiple 

tests resulted in high positive bending moment in the right femur.

Full Break-Over Seat Back

The full break-over seat back configuration was evaluated with 

four tests, including one specifically designed to generate worsecase femur compression. The HIC scores for all these tests were 

below the limit, although two were over 900, suggesting a limited 

margin of safety. Test A13002 produced a high Nij value when 

the tray table deployed and caught beneath the ATD’s chin. The 

Tibia Index was exceeded in test A13001, in which the lower legs 

were initially forward. 

Test A13007 included a rigid plate mounted to the forward 

seat at the location of probable knee strike. This test produced 

high femur compression; however, it did not exceed the limit 

(1,950 lb measured vs. 2,250 lb limit). This test also resulted in 

an artificially high Tibia Index due to impingement on the knee 

plate, and therefore should be considered an anomaly and not 

included in the analysis. All other leg injury parameters were less 

than the limits. 

Table 2. Test Matrix 

Test # Torso Hand Legs Seat Back Seat 

Pitch Belt Type

A12036 Braced Top of fore seat back Back Locked out 30.4 2-point

A12037 Upright Top of thighs Back Locked out 30.4 2-point

A12038 Upright Top of thighs Vertical Locked out 30.5 2-point

A13001 Braced Top of fore seat back Forward Full breakover30.5 2-point

A13002 Upright Top of thighs No Floor Full breakover30.3 2-point

A13003 Braced Top of fore seat back Back EA break-over 30.4 2-point

A13004 Upright Top of thighs Vertical EA break-over 30.3 2-point

A13005* Braced Top of fore seat back Back EA break-over 30.4 2-point

A13007 Upright Top of thighs Back Knee Plate 30.9 2-point

A13008 Braced Back of head Back EA break-over 29.9 2-point

A13009 Pike Back of head Back Locked out 37.8 2-point

A13010 Upright Top of thighs No Floor Locked out 33.6 2-point

A13011 Braced Side of legs Back EA break-over 30.3 2-point

A13012 Braced Side of legs Back Full breakover30.3 2-point

A13013 Braced Side of legs Back Locked out 30.3 2-point

A13014 Pike Side ankles Back Nomex Wall 35.6 2-point

A13015 Pike Side of legs Back Nomex Wall 34.8 y-belt

*Occupant in the Front Seat
12

Table 3. Locked-out Seat Back Test Summary

Test parameter Criteria 

Limit Test Number

A12036 A12037 A12038 A13009 A13010 A13013

Torso Position Braced Upright Upright Pike Upright Braced

Hand Position Seat Back 

Top

Thigh 

Top

Thigh 

Top

Down by 

legs Thigh Top Down by legs

Leg Position Back Back Vertical Back No Floor Back

Restraint Lap belt Lap belt Lap 

belt Lap belt Lap belt Lap belt

Seat Pitch 30.4 30.4 30.5 37.8 33.6 30.3

Impact Velocity (ft/s) 45.2 45.1 45.2 44.7 44.7 44.9

Impact Acceleration (g) 17.1 17.1 17.4 16.7 16.8 16.5

HIC 1000 335 1004 1285 262 520 167

Nij 1.0 0.45 0.83 0.85 0.63 1.57 0.52

Upper Neck Tension (lb) 937 368 652 768 359 893 305

Upper Neck 

Compression (lb) -899 -110 -42 -137 -258 -27 -182

Knee Slider (in) 0.6 0.0 0.0 0.1 0.0 0.1 0.0

Right Tibia 

Compression 

(Upper) (lb)

-1800 -626 -784 -810 -639 -199 -435

Right Tibia 

Compression 

(Lower) (lb)

-1800 -639 -806 -789 -650 -119 -433

Left Tibia Compression 

(Upper) (lb) -1800 -25 -41 -108 -56 -474 -39

Left Tibia Compression 

(Lower) (lb) -1800 -19 -29 -138 -52 -390 -36

Right Leg TI (Upper) 1.0 0.59 0.50 0.37 0.88 0.84 0.58

Right Leg TI (Lower) 1.0 0.69 0.83 0.32 0.62 0.83 0.34

Left Leg TI (Upper) 1.0 0.24 0.40 0.72 0.60 0.67 0.30

Left Leg TI (Lower) 1.0 0.11 0.18 0.43 0.23 0.31 0.18

Peak Knee Velocity 

(ft/s) 11.3 12.8 12.3 12.9 25.2 13.7

Right Femur 

Compression (lb) 2250 -21 -103 -567 -256 -98 -16

Left Femur 

Compression (lb) 2250 -28 -340 -509 -71 -110 -25

Positive Right Femur 

My (in-lb) unknown 2480 3334 2718 2373 998 1682

Negative Right Femur 

My (in-lb) 2655 -141 -116 -656 -303 -1855 -113

Positive Left Femur 

My (in-lb) unknown 873 1165 1667 1654 531 942

Negative Left Femur 

My (in-lb) 2655 -162 -133 -1014 -219 -1821 -144
13

Table 4. Full Break-Over Seat Back Test Summary

Test parameter Criteria 

Limit Test Number

A13001 A13002 A13007* A13012

Torso Position Braced Upright Upright Braced

Hand Position Seat Back Top Thigh Top Thigh Top Down by legs

Leg Position Forwards No floor Back Back

Restraint Lap Belt Lap Belt Lap Belt Lap Belt

Seat Pitch 30.5 30.3 30.9 30.3

Impact Velocity (ft/s) 45.4 45.3 45.4 44.9

Impact Acceleration (g) 17.0 17.6 17.4 16.7

HIC 1000 965 436 920 408

Nij 1.0 0.79 1.39 0.74 0.43

Upper Neck Tension (lb) 937 410 741 790 378

Upper Neck Compression (lb) -899 -513 -2 -146 4

Knee Slider (in) 0.6 0.1 0.1 0.2 0.0

Right Tibia Compression 

(Upper) (lb) -1800 -793 -87 -353 -547

Right Tibia Compression 

(Lower) (lb) -1800 -554 -46 -348 -536

Left Tibia Compression 

(Upper) (lb) -1800 -69 -78 -110 -21

Left Tibia Compression 

(Lower) (lb) -1800 -57 -110 -51 -22

Right Leg TI (Upper) 1.0 1.06 0.59 0.70 0.58

Right Leg TI (Lower) 1.0 1.00 0.29 0.21 0.43

Left Leg TI (Upper) 1.0 0.79 0.72 1.16 0.37

Left Leg TI (Lower) 1.0 0.57 0.32 0.27 0.16

Peak Knee Velocity (ft/s) 10.7 12.0 11.9 9.4

Right Femur

Compression (lb) 2250 -878 -75 -1337 -157

Left Femur 

Compression (lb) 2250 -692 -305 -1949 -10

Positive Right Femur 

My (in-lb) unknown 1480 635 3135 1847

Negative Right Femur 

My (in-lb) 2655 -1256 -959 -133 -124

Positive Left Femur 

My (in-lb) unknown 67 609 2568 976

Negative Left Femur 

My (in-lb) 2655 -692 -1422 -122 -137

* Knee Plate
14

Table 5. Energy Absorbing Seat Back Test Summary

Test parameter Criteria 

Limit Test Number

A13003 A13004 A13005* A13008 A13011

Torso Position Braced Upright Braced Braced Braced

Hand Position Seat Back Top Thigh Top Seat Back Top Back of Head Down by legs

Leg Position Back Vertical Back Back Back

Restraint Lap Belt Lap Belt Lap Belt Lap Belt Lap Belt

Seat Pitch 30.4 30.3 30.4 29.9 30.3

Impact Velocity (ft/s) 45.5 45.4 44.4 44.6 44.9

Impact Acceleration (g) 18.0 17.9 16.6 16.6 16.8

HIC 1000 1095 743 760 411 224

Nij 1.0 0.83 0.87 0.90 0.66 0.51

Upper Neck Tension (lb) 937 705 623 495 403 327

Upper Neck 

Compression (lb) -899 -49 -4 -158 -91 -6

Knee Slider (in) 0.6 0.0 0.2 0.0 0.0 0.0

Right Tibia Compression 

(Upper) (lb) -1800 -652 -815 -611 -533 -531

Right Tibia Compression 

(Lower) (lb) -1800 -660 -843 -616 -535 -523

Left Tibia Compression 

(Upper) (lb) -1800 -28 -139 -34 -29 -32

Left Tibia Compression 

(Lower) (lb) -1800 -27 -137 -33 -29 -31

Right Leg TI (Upper) 1.0 0.56 0.63 0.58 0.70 0.66

Right Leg TI (Lower) 1.0 0.68 0.28 0.67 0.53 0.41

Left Leg TI (Upper) 1.0 0.40 1.37 0.39 0.28 0.29

Left Leg TI (Lower) 1.0 0.41 0.70 0.33 0.18 0.15

Peak Knee Velocity (ft/s) 14.3 13.3 14.7 12.7 N/A

Right Femur

Compression (lb) 2250 -5 -28 -19 -13 -7

Left Femur 

Compression (lb) 2250 -9 -564 -17 -17 -29

Positive Right Femur 

My (in-lb) unknown 2572 3518 2650 2516 1498

Negative Right Femur 

My (in-lb) 2655 -144 -34 -203 -138 -82

Positive Left Femur 

My (in-lb) unknown 2104 1370 2243 1709 800

Negative Left Femur 

My (in-lb) 2655 -117 -165 -165 -199 -112

*Occupant in the Front Seat
15

Energy Absorbing (EA) Break-Over Seat Back 

The energy absorbing break-over seat back configuration 

was evaluated with five tests. As expected, the HIC scores for 

the upright occupant were below the limit. However, the HIC 

value for the occupant in the current brace condition (A13003) 

exceeded the limit. Subsequent tests with an occupant in the 

front seat (A13005) and two tests with modified hand positions 

(A13008 and A13011) produced HIC values below the limit. 

All tests produced neck loads below the limits. The leg injury 

criteria were generally favorable, although multiple tests resulted 

in high positive bending moment in the right femur, one test 

(A13004) produced a high Tibia Index in the upper portion of 

the left tibia.

Bulkhead 

Two tests were run with the occupant behind a bulkhead. 

The initial test (A13014) positioned the occupant slightly beyond the minimum allowable distance of 35 in and included 

a standard lap belt. While the HIC value was quite low (211), 

extreme neck compression was observed. Subsequently, a test 

was run incorporating a Y-belt, which is common for this seating configuration. The Y-belt reduced the forward motion of the 

occupant, while nearly eliminating the neck compression. Both 

tests produced low values for all of the leg parameters, in part 

because the knees did not contact the bulkhead.

DISCUSSION

Injury Risk Evaluation

The current injury criteria required for certification of an 

airplane seat were based upon the data and instrumentation 

available in the 1980s, when the regulations were implemented. 

These regulations did not specifically address all potential neck 

and leg injury mechanisms. To analyze whether the current 

certification injury criteria and test device are adequate to evaluate the potential injury for the evolving seat designs, newer leg 

injury and neck injury criteria were evaluated, in addition to 

the existing criteria. 

Neck Injury 

In the row-to-row tests, all but two of the test configurations, 

including the configurations with the occupant upright, had neck 

injury values below limits. The two row-to-row cases that had 

high neck loads were produced by an unusual loading scenario. 

Table 6. Bulkhead Test Summary

Test Parameter Criteria Limit Test Number

A13014 A13015

Torso Position Pike Pike

Hand Position Down by legs Down by legs

Leg Position Back Back

Restraint Lap Belt Y-Belt

Seat Pitch (in) 35.6 34.8

Impact Velocity (ft/s) 45.0 45.2

Impact Acceleration (g) 16.4 16.6

HIC 1000 211 106

Nij 1.0 2.02 0.50

Upper Neck Tension (lb) 937 96 303

Upper Neck Compression (lb) -899 -2399 -28

Knee Slider (in) 0.6 0.0 0.0

Right Tibia Compression (Upper) (lb) -1800 -289.0 -206.0

Right Tibia Compression (Lower) (lb) -1800 -258.0 -185.0

Left Tibia Compression (Upper) (lb) -1800 -52 -21

Left Tibia Compression (Lower) (lb) -1800 -51 -24

Right Leg TI (Upper) 1.0 0.37 0.28

Right Leg TI (Lower) 1.0 0.21 0.11

Left Leg TI (Upper) 1.0 0.43 0.30

Left Leg TI (Lower) 1.0 0.23 0.17

Peak Knee Velocity (ft/s) N/A 12.9 -

Right Femur Compression (lb) 2250 -19 -5

Left Femur Compression (lb) 2250 -30 -16

Positive Right Femur My (in-lb) unknown 730 765

Negative Right Femur My (in-lb) 2655 -422 -145

Positive Left Femur My (in-lb) unknown 666 828

Negative Left Femur My (in-lb) 2655 -419 -148
16

In three of the tests, the tray table deployed in a manner that 

caused it to catch under the ATD’s chin. In one case, the table 

released prior to head impact, and in the other two, the ATD’s 

head struck the tray table latch, freeing the table (Fig. 16). This 

interaction momentarily interrupted the forward travel of the 

ATD, resulting in very high neck loads. The combined neck 

bending-tension criteria Nij were exceeded in two cases, and 

it was below the criteria in the third. One of these tests also 

nearly exceeded the neck tension criteria. Catching the chin on 

the tray table can produce serious injury. The Hybrid II ATD, 

typically used in dynamic tests conducted to qualify new seat 

designs, cannot directly measure the interaction with a tray table 

that has deployed, leaving conservative qualitative assessments 

as the only means to ensure the safety of the interaction. The 

neck instrumentation in the FAA Hybrid III can assess the risk 

of cervical spine injury due to applied forces, but neither ATD 

can measure contact forces that could cause serious soft tissue 

injury such as a collapsed larynx. In the absence of a soft tissue 

injury assessment method, avoiding impingement onto hard 

structures may be the best means of preventing neck injury. 

The test matrix also included a rigid wall to assess the axial 

loading in the neck. In the first test, the standard two-point 

belt was installed, resulting in head impact with the wall. This 

contact lead to high compressive loading in the cervical spine, 

as well as a value of the neck injury criteria that was over double 

the regulatory limit. In the second test, a Y-belt restraint was 

installed, which reduced the distance that the ATD traveled 

sufficiently to prevent contact of its head with the rigid wall. 

Without contact, the neck forces were primarily tensile due to 

inertial loading, resulting in a neck injury value that was only 

half the regulatory limit. 

Shoulder injury

Based on the injuries seen in the Hudson River ditching, 

shoulder injury was evaluated. Hyper-extension of the shoulder 

joint in the sagittal plane was a possible injury mechanism for 

brace positions that place the hands on the seat back. There 

was no indication that the ATD interaction with any of the 

seatback types resulted in hyper-extension, as observed in the 

videos and evidenced by inspection of the shoulder stop bolt, 

which remained intact throughout the study. 

Femur compression

Even at a relatively close pitch (30 in), none of the tests of 

representative seats resulted in significant femur compression. In 

many cases, the femur load was primarily tension that occurred 

as the pelvis was constrained by the lap belt before the knee 

contacted any structure. For one test, a rigid vertical plate was 

attached to the target seat in front of the aft occupant’s knees. 

This worst case condition still did not produce femur compression that exceeded the injury limit. It is possible that testing in 

a yaw condition could asymmetrically load the legs and increase 

the load somewhat, but that increase would have to be over 15% 

to exceed the injury limit. 

Femur bending

In test configurations where the knee vertical motion was 

constrained by the position of the lower leg, forward rotation 

of the pelvis produced significant positive femur Y-axis bending. 

The moments measured were less than the European regulatory 

limit [21] but exceeded the EEVC limit in cases where the ATD 

legs were in the aft position and the torso was either upright or 

in the current brace position. Both the biofidelity of the moment produced and the applicability of the EEVC limit for these 

loading cases are unknown. 

In test configurations where the lower legs flailed forward, the 

upper legs were forced downward against the front of the seat 

frame as the pelvis rotated forward, producing a significant negative Y-axis bending moment. The EEVC femur bending criteria 

may be useful in evaluating the injury risk posed by this loading 

since it is similar to the loading cases for which that criterion 

was derived, i.e., a three-point bending scenario. Some injuries 

in the Kegworth crash were attributed to this type of loading 

[26]. For the tests that produced significant negative bending, 

the moment was always less than the EEVC limit. 

Tibia-femur displacement

Although in some tests the tibia, rather than the knee, was 

the primary load path for the interaction with the target seat, 

the loading generated was not high enough to cause significant 

tibia-femur displacement in any of the tested configurations. 

Tibia compression 

The magnitude of tibia compression produced in all test 

configurations was less than half of the criteria limit, and is 

therefore not a likely injury mechanism.

Tibia bending-compression combined criteria 

The Tibia Index was over the biomechanical limit of 1.0 in 

only two cases (excluding the knee plate scenario), with one of 

these also exceeding the EU regulatory limit of 1.3. The legs 

were positioned forward or vertical in these cases. This initial 

position allows the tibia to contact the seat frame before or at the 

same time as the knee. This produced bending in the tibia as the 

momentum of the leg below the seat frame, and the inertial force 

of the upper leg, load the ends of the tibia. In the case with a TI 

over the European limit, the seat cushion slid forward with the 

Figure 16. Chin of ATD Catching on 

Tray Table
17

pelvis, which apparently caused the ATD to travel further than 

usual. This motion could help explain why this test produced a 

TI that was much higher (1.37) than other seat configurations. 

The unsupported (no floor) test configurations were specifically 

set up to evaluate the risk of tibia injury when the occupant’s 

lower legs are free to swing forward and impact the seat frame. 

Neither of these “worst case” tests resulted in a TI over the limit. 

Note that interaction between the rigid knee plate and the lower 

leg also produced high TI values, but this special configuration 

was not considered a valid evaluation of lower leg injury risk 

because the plate's shape and stiffness was not representative 

of an actual aircraft seat. In this test series, the TI results were 

quite dependent on leg initial position because it affected the 

orientation of the leg when it interacted with the seat frame 

structure. This indicates that the TI is sensitive to the shape and 

stiffness of the forward seat’s structure and the seat pitch, since 

both of these factors could affect where the loads are applied to 

the tibia and the magnitude of those loads. Given the low injury 

potential observed in this study, there does not now appear to 

be a benefit to adopting lower leg injury criteria. 

Brace Position Evaluation

Current brace position 

The occupants place their hands on the top of the seat back 

and their head against the seat back, as shown in AC 121-24B. 

This position was successful in reducing head and neck injury 

risk in only one scenario, when the seat back in front was a 

locked-out type. When the seat back in front was the full break 

over or energy absorbing type, the resulting head injury criteria 

were near or over the criteria limit, while the neck criterion were 

below limits. In these cases, the arms pushed the seat back away 

from the occupant, allowing the head to accelerate relative to 

the seat back, producing significant relative velocity between 

the head and seat back. Pushing the seat back away resulted in 

an impact point lower on the seat back, nearer the hinge joint. 

This lower point would tend to provide a stiffer response than 

a point higher up on the seatback. Both the high velocity and 

the high stiffness of the impact surface tend to increase the 

severity of the head impact. In one test with an EA seat back, 

the front row was occupied. This reduced how far the seat back 

could fold forward, altering the impact point and stiffness with 

respect to the unoccupied case, decreasing the head injury risk. 

The interaction with the full break-over and energy absorbing 

seat backs tended to increase the neck injury risk, but the criteria 

values did not exceed the limits. 

Leg placement

Initial leg position did not appear to have a significant effect 

on upper torso and head interaction with the seat back and 

similarly, the upper torso initial position appeared to have little 

effect on leg injury assessment values. This permitted independent 

evaluation of each factor.

Vertical position

This position resulted in moderate-to-high TI values. It also 

produced moderate femur compression values and positive femur 

Y-axis bending moments. 

Forward position

This position resulted in a TI value that was just over the 

limit. It also produced moderate femur compression values and 

significant levels of positive and negative femur Y-axis bending 

moments. 

Aft position

This leg position tended to prevent forward translation of 

the lower legs, which in turn prevented contact with the front 

seat, significantly reducing loads on the lower leg. This position 

produced positive Y-axis bending moment, but it prevented 

femur contact with the front of the seat frame and the associated negative Y-axis bending. Of course, this position will only 

provide these advantages for occupants whose lower legs are long 

enough for their feet to firmly touch the floor.

Alternate brace position 

The occupants place their head directly on the seat back in 

front of them, and their hands down by the side of their lower 

legs. The primary factor affecting the effectiveness of the current brace position was the interaction between the occupant’s 

arms and the seat back. To reduce this interaction, the current 

position was modified by placing the hands down by the lower 

legs instead of on the seat back (Fig. 17). Because the arms were 

positioned to prevent them from pushing the seat back forward 

during the impact, the head remained in contact, which reduced 

head and neck injury risk. This “alternate” position was successful in reducing head and neck injury risk for all of the seat back 

types evaluated. This position (when combined with the “Aft” 

leg position ) prevented lower leg contact with the seat in front 

and produced negligible femur axial compressive forces, lower 

(positive) femur Y-axis bending forces, and prevented femur 

contact with the front of the seat frame . Improving performance 

Figure 17. Alternate Brace Position
18

with the EA seat back was of particular importance since they 

will eventually be the most prevalent seat back type in service 

as newer aircraft with dynamically qualified seating systems are 

added to the fleet.

Pike position 

In the current guidance, the pike position is the one where 

the seat in front is too far away to support the head, or there is 

no seat in front, as in a bulkhead row. This position was successful in reducing head and neck injury risk in a row-to-row 

application. The tested configuration used a locked-out seat 

back to provide a worst case overall stiffness, and a seat pitch 

(38 in) selected to maximize the head impact velocity. This 

configuration is representative of a long pitch configuration 

with an average-size occupant, or a shorter pitch configuration 

with a shorter statured occupant. During the test, the head 

contacted the seat back, but the combination of low-impact 

velocity and relatively soft local compliance of the point on 

the seat back struck (center of the tray table) contributed to 

the low HIC and Nij values. When seated behind a wall 35 

in from the seat reference point, this position reduced head 

injury risk but permitted significant neck loading. The compressive load in the upper neck load cell was 2,399 lb and 

the Nij value was 2.02, both of which are more than double 

the criteria limits. While these results are concerning, they 

may not be typical for occupants of seat places behind interior walls. Because of the risk of head injury for occupants 

of conventional seats placed behind walls at the minimum 

allowable distance of 35 in, many aircraft meeting the head 

impact protection requirements of 14 CFR 25.562 (c) have 

seats at these locations that incorporate “head path reducing 

features” such as Y-belts, and seat frames designed to flex less 

under load [27]. To investigate this more likely scenario, the 

previous test was repeated with the ATD seated in a front 

row type of seat, restrained by a Y-belt. In this seat configuration, the Y-belt and seat frame stiffness effectively limited the 

occupant horizontal head excursion to 5 in from the initial 

position, which did not allow the ATD to contact the wall 

in front, significantly reducing head and neck injury risk. 

LIMITATIONS

Effect of Combined Loading 

Being subjected to combined vertical/horizontal loads 

while in the current or proposed brace positions could alter 

the spinal injury risk, compared to the upright position due 

to spinal misalignment. An evaluation of this difference in 

injury risk requires data relating injury tolerance to spine 

bending angle, which is currently not available. Since the 

current and alternate brace positions result in a similar initial 

torso angle and torso kinematics, a difference in spinal injury 

risk is not expected.

Seat Back Range of Stiffness

The three types of seat backs used in this study are representative of the range stiffness of seat backs contained in the 

US fleet. The locked-out and full break-over seat backs are 

typical for older aircraft that were not required to meet the 

head impact protection requirements of 14 CFR 25.562 (c) 

[9]. They represent the stiffest (locked-out) and softest (full 

break-over) hinge properties. Seats utilizing EA seat backs 

are typically found in aircraft designed since 1988 that must 

meet the provisions of 14 CFR 25.562, although they can be 

installed as replacements in other aircraft as well. Since FAA 

regulations require that seats meeting §25.562 be installed 

in all newly manufactured transport aircraft operated in 

passenger carrying operations after October 27, 2009, EA 

seat backs will eventually be the prevalent seat back type in 

service as newer aircraft with dynamically qualified seating 

systems are added to the fleet. The stiffness of EA seat backs 

varies between different seat manufacturers and different seat 

models, but only one type of EA seat back was used for this 

study. Since the alternate brace position was effective for the 

range of stiffness evaluated, and EA seat backs, in general, 

provide a resistance that falls somewhere between the lockedout and the full break-over, the effectiveness of the position 

should extend to other EA seat backs.

Seat Back Distribution

The percentage of the seats in the fleet with seat back characteristics that tend to reduce the effectiveness of the current 

brace position (arms on seat back) is unknown. Using data 

retrieved from the FAA’s Safety Performance Analysis System 

(SPAS) on June 25, 2008, it was estimated that 37% of the 

fleet met either all the requirements of §25.562 or at least the 

structural integrity requirements in §25.562 [28]. This total 

does not include seats on aircraft initially delivered without 

improved seats, but which had them installed later. The fully 

compliant seats are assumed to contain EA seat backs. The 

lack of information makes it difficult to determine the immediate benefit of changing the brace position. However, as 

the number of EA seats within the fleet increases, the benefit 

will increase.

Test Repeatability

Due to the limited number of test articles, exact test conditions were not repeated. Previous testing at CAMI yielded 

HIC variation of less than 100 HIC points on impacts onto 

EA seat backs, while impacts onto homogenous surfaces had 

less points [11]. Testing repeatability for the other injury parameters are unknown but should to be of a similar magnitude. 
19

CONCLUSIONS

We conducted research into transport aircraft passenger brace 

position effectiveness and leg injury risk. The test configurations 

were derived to evaluate several factors including: seat back 

resistance to folding over, the currently recommended brace 

positions and alternate positions, the spacing between rows of 

seats, occupant stature, and interaction with the floor and interior 

walls. Injury risks were evaluated using an advanced test dummy 

and injury criteria from current FAA regulations, Federal Motor 

Vehicle Safety Standards, European auto safety regulations, and 

applicable research findings. Analysis of the results led to the 

following conclusions:

•	 Neck injury: Neck injury was not found to be a significant 

risk in the row-to-row seating configurations evaluated unless 

the chin of the ATD catches the top of the tray table. 

•	 Upper Leg Injury: Even in the worst case test condition, the 

femur axial compressive force was below the regulatory limit 

indicating that the femur compression criteria currently cited 

in FAA regulations is not likely to be exceeded in passenger 

seat dynamic qualification tests. While high negative bending 

moments were not observed in this test series, injuries in the 

Kegworth crash (attributed to femur bending) suggest that this 

type of loading may be more useful injury criterion. However 

additional research is necessary to determine the biofidelity of 

the moments produced by the ATD and to establish appropriate pass/fail limits before any such criteria could be adopted. 

•	 Lower Leg Injury: Given the low injury potential observed 

in this study, there does not appear to be a benefit to adopting 

lower leg injury criteria at this time.

•	 Current Brace Position: This position (head against the seat 

back, hands on top of the seat back) was evaluated for three 

common types of seat backs. This position was only successful 

for locked-out type seat backs. For full break-over and energy 

absorbing type seat backs, the ATD’s arms pushed the seat back 

away, allowing the head to accelerate relative to the seat back, 

increasing the severity of the head impact. There was, however, 

no evidence that the ATD interaction with any of the seatback 

types resulted in hyper-extension of the shoulder joint. The 

“Forward” and “Vertical” leg brace positions permitted the 

lower legs to flail forward and contact the seat in front. This 

contact produced femur bending and compression (below 

criteria limits), and tibia injury risk in some cases. The “Aft” leg 

brace position reduced lower leg flailing and prevented femur 

contact with the front of the seat frame. This position resulted 

in low femur and tibia injury assessment values; however, it 

is only achievable for occupants whose lower legs are long 

enough for their feet to firmly touch the floor. 

•	 Alternate Brace Position: To reduce the detrimental interaction between the occupant’s arms and the seatback, the current 

position was modified by placing the hands down by the lower 

legs instead of on the seat back. This “Alternate” position was 

successful in reducing head and neck injury risk for all of the 

seat back types evaluated. 

•	 Pike Position: This position is currently recommended when 

the seat in front is too far away to support the head, or there 

is no seat in front, as in a bulkhead row. It was successful in 

reducing head and neck injury risk in the row-to-row scenario, as long as the struck seat back has a relatively soft local 

compliance at the point of impact. When seated behind a 

bulkhead, the effectiveness of the pike position was dependent 

on whether the head of the occupant struck the bulkhead. 

“Head-path-reducing features,” such as Y-belts, prevented 

head contact at the typical 35-in setback. 

This study used an idealized impact condition to evaluate the 

dynamic performance of seats and occupants. While these types 

of tests are useful for comparison purposes, they cannot predict 

brace position performance or injury risk in all possible impact 

scenarios. The observations and recommendations made concerning the effectiveness (or ineffectiveness) of the brace positions 

studied should be applied taking that fact into consideration. 

These findings are based purely on results of impact tests with 

ATDs, and further study is necessary to determine whether the 

Alternate position is practical to implement from a human factors perspective. This research has led to the determination that 

as seat technology has evolved, the most effective brace position 

has as well; the current positions recommended in AC 121-24B 

may need some adjustment to provide an equivalent level of 

safety for all passenger seat back types. 

REFERENCES

1. National Transportation Safety Board. Survivability of accidents involving Part 121 U.S. Air Carrier Operations, 

1983 through 2000. NTSB Report Number SR01/01. 2001.

2. Discovery Channel. Mythbusters series number 33, Killer 

Brace Position, Episode 43, June 22, 2005, Mythbusters 

2005 Episode Guide. 

3. Chandler R. Brace for impact. Positions, Proceedings of the 

Fifth Annual International Aircraft Cabin Safety Symposium, 

Cosponsored by the University of Southern California, the 

FAA (Western Pacific Region), and the Southern California 

Safety Institute, February 1988.

4. Civil Aviation Authority. Occupant modelling in aircraft 

crash conditions (CAA Paper no. 900012). London: CAA, 

1990. 

5. SAE Aerospace Recommended Practice 4771. Recommended Brace Positions, Warrendale, PA: SAE International, 2008.

6. National Transportation Safety Board. Safety Recommendation A10-78. Washington, DC: NTSB. 2010.

7. Sperber M, Brace/Safety positions for passengers, cabin and 

cockpit crew in emergency landing situations, Sixth Triennial 

International Fire and Cabin Safety Research Confrence, 

Atlantic City NJ, Session: Cabin Safety I, 10/26/2010, TUV 

Rheinland Group.

8. Gowdy V, DeWeese R, Beebe M, Wade B, Duncan J, Kelly 

R, Blaker J. A Lumbar spine modification to the Hybrid 

III ATD for aircraft seat tests. Warrendale, PA: SAE International, 1999.
20

9. US Code of Federal Regulations. Title 14, Part 25.562. 

Airworthiness standards: Transport category airplanes, emergency landing conditions. Washington, DC: US Government 

Printing Office, 1988. 

10. Federal Aviation Administration Advisory Circular 25-17A. 

Transport airplane cabin interiors crashworthiness handbook. 

Washington, DC: Federal Aviation Administration, 2009. 

11. DeWeese R, Moorcroft D. Evaluation of a head injury criteria 

component test device (Report No. DOT/FAA/AM-04/18). 

Washington, DC: Federal Aviation Administration Office 

of Aerospace Medicine, 2004.

12. SAE International. Aerospace Standard 8049b. Performance standard for seats in civil rotorcraft, transport 

aircraft, and general aviation aircraft. Warrendale, PA: 

SAE International, 2005. 

13. SAE International. Instrumentation for impact test – Part 

1- Electronic instrumentation. Warrendale, PA: SAE International; 2014; Surface Vehicle Recommended Practice 

No: J211-1.

14. SAE International. Sign convention for vehicle crash testing. 

Warrendale, PA: SAE International; Dec. 1994; SAE Surface 

Vehicle Information Report No: J1733.

15. SAE International. Instrumentation for impact test – Part 

2- Photographic instrumentation. Warrendale, PA: SAE 

International; 2014; SAE Surface Vehicle Recommended 

Practice No: J211-2.

16. Data Processing Vehicle Safety Workgroup. Crash analysis 

criteria description, Version 1.6.2. The Workgroup; April 

2005; accessed Aug. 2006 from: www.crashnetwork.com 

17. Kuppa S. Injury criteria for side impact dummies, Washington, DC: DOT/National Highway Traffic Safety 

Administration; May 2004. FMVSS-214 NPRM docket: 

NHTSA-2004-17694.

18. AAAM. The Abbreviated Injury Scale 2005. Barrington, 

IL: Association for the Advancement of Automotive 

Medicine, 2008. 

19. US Code of Federal Regulations, Title 49, Part 571.208. 

Occupant crash protection. Washington, DC: US Government Printing Office, 2011. 

20. Kuppa S, Wang J, Haffner M, Eppinger R. Lower extremity injuries and associated injury criteria, Washington, DC: 

DOT/National Highway Traffic Safety Administration; May 

2007. NHTSA paper no. 457.

21. European Union. 2009. “Directive 2009/78/EC of the European Parliament and of the Council of 14 January 2009 

on the type-approval of motor vehicles with regard to the 

protection of pedestrians and other vulnerable road users, 

amending Directive 2007/46/EC, and reapealing Directives 

2003/102/EC and 2005/66/EC.” Official Journal of the 

European Union L 35/10, http://europa.eu.int

22. European Enhanced Vehicle-Safety Committee. EEVC 

working group 17 report: Improved test methods to evaluate 

pedestrian protection afforded by passenger cars. Delft, The 

Netherlands: TNO Crash-Sagety Research Center, 2002.

23. Kennedy E, Hurst W, Stitzel J, Cormier J, Hansen G, Smith 

E, Duma S. Lateral and posterior dynamic bending of the 

mid-shaft femur: Fracture risk curves for the adult population. Stapp Car Crash J. 2004 Nov;48:27–51. 

24. Mertz H. Anthropomorphic test devices. Accidental injury, 

biomechanics, and prevention, edited by Nahum A and 

Melvin HJ, Springer-Verlag. 1993.

25. Federal Aviation Administration. Dynamic evaluation of 

seat restraint systems and occupant protection on transport 

airplanes. Advisory Circular 25-562-1B. Washington, DC: 

Federal Aviation Administration, 2006.

26. Brownson P, Rowles J, Wallace W, Anton D. The mechanism 

of femoral fracture in an impact accident. Aviation, Space, 

and Environmental Medicine. 1998 Oct; 69:971-974.

27. Gowdy V, DeWeese R. Evaluation of head impact kinematics for passengers seated behind interior walls (Report No. 

DOT/FAA/AM-92/20). Washington, DC: Federal Aviation 

Administration Office of Aerospace Medicine, 1992.

28. DeWeese R, Moorcroft D, Taylor A. Aviation child safety 

device performance standards review (Report No. DOT/

FAA/AM-11/3). Washington, DC: Federal Aviation Administration Office of Aerospace Medicine, 2011.

29. Moorcroft D, DeWeese R, Taylor A. “Improving test repeatability and methods,” The Sixth Triennial International Fire 

& Cabin Safety Research Conference, Oct 25-28, 2010.
A1

APPENDIX A APPENDIX A

Test Analysis

Braced position with arms on seat back, locked-out seat back, legs back

(Figures A1 to A3)

Figure A1 – A12036 T=0 ms

Figure A2 – A12036 T=120 ms

Figure A3 – A12036 T=150 ms

• The ATD is positioned with the torso forward and head against the seat back. The hands are resting on the 

top of the seat back in front, the legs are back as far as was allowed by the baggage bar.

• The arms place a load on the seat back in front causing it to move forward some, but because the seat back 

is the locked out type, it does not move significantly away from the ATD’s head during the test. The 

continuous contact maintained between the head and the seat back was one factor in the relatively low HIC 

of 335.

• The right foot did not slide forward and the left foot slid forward until the lower leg was nearly vertical. 

The knees translated forward and contacted the seat back. The aft-ward position of the feet appeared to 

prevent lower leg flailing. No significant femur compression loads were generated; however, the Y-axis 

positive moment in the right femur (2480 in-lb) was relatively high.
A2

Upright position with a locked out seat back, legs back 

(Figures A4 to A6)

Figure A4 – A12037 T=0 ms

Figure A5 – A12037 T=125 ms

Figure A6 – A12037 T=177 ms

• The ATD was positioned with the torso upright and the legs back as far as was allowed by the baggage bar, 

the hands were placed on top of the thighs. 

• The hands come forward in the early stage of the test and begin to push the seat back away from the 

occupant. This motion permits the head to travel further and hit the seat back at a lower point than if the 

seat back had remained in the nominal upright position. The high head impact velocity (51 ft/s) relative to 

the seat and higher overall stiffness of the point on the seat back where the head struck resulted in a HIC of 

1004, which exceeds the limit. 

• The feet slid forward in unison with the knee excursion. The knees contacted the seatback. The aft-ward 

position of the feet appeared to prevent lower leg flailing. Low femur compression loads were generated 

and the positive Y-axis moment in the right femur (3334 in-lb) was relatively high.
A3

Upright position with a locked out seat back, legs vertical

(Figures A7 to A9)

Figure A7 – A12038 T=0 ms

Figure A8 – A12038 T=125 ms

Figure A9 – A12038 T=170 ms

• The ATD was positioned with the torso upright, the legs vertical, and the hands placed on top of the thighs. 

This is the initial position used for seat qualification tests.

• The hands come forward in the early stage of the test and begin to push the seat back away from the 

occupant. This motion permits the head to travel further and hit the seat back at a lower point than if the 

seat back had remained in the nominal upright position. The high head impact velocity (52 ft/s) relative to 

the seat and higher overall stiffness of the point on the seat back where the head struck resulted in a HIC of 

1,285, which exceeds the limit.

• The feet slid forward in unison with the knee excursion until the knees contacted the seatback, generating 

low compression loads. As the torso and pelvis rotated forward, a positive Y-axis bending torque was 

generated in the right femur (2718 in-lb) that was relatively high. The lower legs moved forward and made

contact with the aft tube of the seat frame but the calculated tibia indices for the legs did not exceed the 

limit. After swinging forward, the angle of the lower legs permitted the knees to translate downward 

significantly. This relieved the positive Y-axis moment but resulted in negative femur Y-axis bending (but 

not close to the limit).
A4

Braced position with arms on seat back, full break over seat back, legs forward

(Figures A10 to A12)

Figure A10 – A13001 T=0 ms

Figure A11 – A13001 T=120 ms

Figure A12 – A13001 T=188 ms

• The ATD is positioned with the torso forward and head against the seat back. The hands are resting on the 

top of the seat back in front, and the legs are as far forward as possible while still contacting the floor. 

• The ATD’s elbows pressed against the seat back, pushing it away from the occupant and folding it 

completely flat just before head contact. This motion permits generation of significant relative velocity 

between the head and the seat back before it strikes the seat back just below the tray table. The resulting 

HIC was 965, which nearly exceeds the limit.

• The lower legs translated forward in unison with the knee, which resulted in contact between the tibia and 

the aft tube of the seat frame. This caused femur compression and positive Y-axis bending (but neither was 

over the limit). The feet maintained contact with the floor as they continued to slide forward. This 

generated a combination of axial compression and bending in the tibia that resulted in a tibia index just 

over 1.0 for the right leg (upper and lower calculations). After swinging forward, the angle of the lower 

legs permitted the knee to translate downward significantly as the torso and pelvis rotated forward. This 

placed the femur in significant negative bending (but not over the limit).
A5

Upright position, full break-over seat, legs unsupported

(Figures A13 to A15)

Figure A13 – A13002 T=0 ms

Figure A14 – A13002 T =120 ms

Figure A15 – A13002 T=196 ms

• The ATD was positioned with the torso upright and hands on top of the thighs. No floor was installed, 

allowing the legs to dangle vertically to emulate a shorter occupant whose feet will not contact the floor.

• The ATD’s arms struck the seat back prior to the head, causing the seat back to move away slightly. The 

head struck the tray table latch shattering it and releasing the tray table. With the tray table loose, the 

ATD’s chin caught on the tray table and hung there as the seat back moved away. This interaction caused 

tension and bending moments in the neck (Nij of 1.39) which exceeded the combined limit.

• The lower legs translated forward in unison with the knee until the knee contacted the seatback. The lower 

legs then rotated forward allowing tibia contact with the aft tube of the seat frame. The calculated tibia 

indices for the legs did not exceed the limit. The angle of the lower legs and the lack of a floor reaction 

surface permitted the knee to translate downward significantly as the torso and pelvis rotated forward. This 

placed the femur in significant negative bending (but not over the limit).
A6

Braced position with arms on seat back, energy absorbing seat back, legs back

(Figures A16 to A18)

Figure A16 – A13003 T=0 ms

Figure A17 – A13003 T=130 ms

Figure A18 – A13003 T=180 ms

• The ATD is positioned with the torso forward and head against the seat back. The hands are resting on the 

top of the seat back in front, and the legs are back as far as was allowed by the baggage bar.

• As the ATD rotated forward, the elbows pressed against the seat back in front, pushing it away from the 

occupant, folding it completely flat just before head contact. This motion permits generation of significant 

relative velocity between the head and the seat back before the head strikes the seat back just below the tray 

table (as in test 13001). The resulting HIC of 1,095 was relatively high.

• The feet slid forward very little and the knees translated forward and contacted the seat back. The seat 

cushion slipped forward during the test which apparently allowed the ATD to translate forward further than 

in a similar test (A12036). This additional excursion did not result in significant femur compression loads. 

The lower legs did not flail forward after contact. As the torso and pelvis rotated forward, a positive Y-axis 

moment was generated in the right femur (2,572 in-lb), that was relatively high.
A7

Upright position, energy absorbing seat back, legs vertical

(Figures A19 to A21)

Figure A19 – A13004 T=0 ms

Figure A20 – A13004 T=120 ms

Figure A21 – A13004 T=150 ms

• The ATD was positioned with the torso upright and the legs vertical. The hands were placed on top of the 

thighs. This is the initial position used for seat qualification tests. 

• The hands come forward in the early stage of the test and begin to push the seat back away from the 

occupant slightly. This seat back motion resulted in the head impacting just below the tray table latch and 

sliding down the seat back as it folded forward. The resulting HIC did not exceed the limit.

• The legs slid forward in unison with the knee translation. The seat cushion slipped forward during the test 

which apparently allowed the ATD to translate forward further than in a similar test (A12038). This 

resulted in knee and upper tibia contact with the lower seat back and seat frame, generating low femur 

compression loads. This interaction prevented the lower legs from flailing forward, but caused significant 

bending in the left upper tibia (TI of 1.37) and right femur (positive Y-Axis moment of 3,518 in-lb). The TI 

exceeded the limit and the Y-Axis moment was relatively high.
A8

Braced position with arms on seat back, energy absorbing seat back, legs back, with a front row occupant

(Figures A22 to A24)

Figure A22 – A13005 T=0 ms

Figure A23 – A13005 T=130 ms

Figure A24 – A13005 T=170 ms

• The ATD is positioned with the torso forward and head against the seat back. The hands are resting on the 

top of the seat back in front, and the legs are back as far as was allowed by the baggage bar. This is the 

same setup and seat configuration as test A13003, but this test also included a front occupant to assess the 

interaction between the seat back and the occupant.

• As the ATD rotated forward, the elbows pressed against the seat back in front pushing it away from the rear 

occupant until the seat back contacted the back of the front row occupant. This interaction limited the seat 

back forward rotation so the rear occupant hit higher on the seat back than in test A13003. The head hit 

towards the bottom of the tray table resulting in a HIC of 760 which was significantly less than the HIC of 

1095 registered in the test without an occupied front seat (test A13003).

• The feet slid forward very little and the knees translated forward and contacted the seat back but did not

result in significant femur compression loads. The lower legs did not flail forward after contact. As the 

torso and pelvis rotated forward, a positive Y-axis moment was generated in the right femur (2,650 in-lb), 

that was relatively high. This is a similar response as in test A13003.
A9

Upright position, full break-over seat, legs back, and a rigid knee contact plate.

(Figures A25 to A27)

Figure A25 – A13007 T=0 ms

Figure A26 – A13007 T=100 ms

Figure A27 – A13007 T=190 ms

• The ATD was positioned with the torso upright and the legs back. The hands were placed on top of the 

thighs, and the legs were as far back as was allowed by the baggage bar. A vertical rigid plate was attached 

to the back of the front seat frame in the knee strike zone.

• After the knees struck the seat, the tray table was released. As the ATD moved forward, the hands 

contacted the seat back, pushing it forward some, creating a gap between it and the loose tray table, which

remained upright. As the ATD continued forward, the neck contacted the tray table which became caught 

under the ATD’s chin. This interaction produced a significant loading of the neck (Nij = 0.74) but did not 

exceed the limit. The table interaction did not prevent the ATD’s head from impacting the seat back. That 

impact destroyed the table latch and produced a HIC of 920, which was near the limit.

• The ATD slid forward until the knees impacted the steel strike plate. This produced a high femur 

compressive force of very short duration followed by a lower oscillating force that continued until the ATD 

rebounded. After the knee impact, the feet slid forward until the lower legs were vertical. Both legs 

exhibited similar response, with femur peak loads of 1,337 lb on the right side and 1,949 lb on the left side

which were both below the limit. The femur positive Y-Axis moments, however, were relatively high, with 

the right side producing 3,135 in-lb, and the left side 2,568 in-lb. This interaction with the strike plate 

prevented lower leg flailing which resulted in high moments in the left tibia. However, lower leg injury was 

not assessed for this test due to the unrealistic interaction between the lower leg and the knee strike plate.
A10

Braced position with hands on top of head, energy absorbing seat back, legs back

(Figures A28 to A30)

Figure A28 – A13008 T=0 ms

Figure A29 – A13008 T=120 ms

Figure A30 – A13008 T=180 ms

• The ATD is positioned with the torso forward and head against the seat back. The hands are on the back of 

the head taped together to stay in place, and the legs are back as far as was allowed by the baggage bar.

• As the ATD rotated forward, the elbows pressed against the seat back in front, pushing it away from the 

occupant. This motion permits generation of significant relative velocity between the head and the seat 

back before it strikes just below the tray table (as in test A13001 and A13003). This seat back did not fold 

completely flat before the head impact. This likely provided more compliance in the area struck; resulting 

in the HIC of 411 which was less that measured in A13001 and A13003, and well below the limit.

• The right foot did not slide forward and the left foot slid forward until the lower leg was nearly vertical. 

The knees translated forward and contacted the seat back but did not generate significant femur 

compression. As the torso and pelvis rotated forward, a positive Y-axis moment was generated in the right 

femur (2,516 in-lb) that was relatively high. This is a similar response as in test A13003.
A11

Pike position with hands on top of head, locked-out seat back, and legs back

(Figures A31 to A33)

Figure A31 – A13009 T=0 ms

Figure A32 – A13009 T=100 ms

Figure A33 – A13009 T=170 ms

• The ATD is positioned with the torso as far forwards as it can go with the abdominal insert removed. This 

position aligns the neck with the horizontal impact vector. The hands are on the back of the head taped 

together to stay in place and the legs back as far as allowed by the baggage bar. The seat pitch was 

increased to 38 inches to provide the necessary space for a 50th percentile occupant to assume this position. 

This setup was intended to emulate a small occupant that cannot brace against the seat back in front when 

seats are installed at a typical economy class pitch.

• The ATD’s arms and top of head struck the middle of the tray table, forcing the seat back to fold over. The 

HIC and neck loads were all well below limits.

• The right foot did not slide forward and the left foot slid forward until the lower leg was nearly vertical. 

The knees translated forward but did not contact the seat back. As the torso and pelvis rotated forward, a 

positive Y-axis moment was generated in the right femur (2373 in-lb) that was relatively high.
A12

Upright Position, locked-out seat back, no floor

(Figures A34 to A36)

Figure A34 – A13010 T=0 ms

Figure A35 – A13010 T=120 ms

Figure A36 – A13010 T=160 ms

• The ATD was positioned with the torso upright and hands on top of the thighs. No floor was installed, 

allowing the legs to dangle vertically to emulate a shorter occupant whose feet will not contact the floor.

The seat pitch (34 inches) was chosen to maximize the ankle velocity at the time of contact between the 

lower leg and the seat frame aft cross tube. 

• The ATD’s arms pushed the seat back slightly away from the occupant, as seen in previous tests, causing 

the head to strike the tray table latch. This impact released the table allowing it to catch under the ATD’s 

chin. During a typical impact onto a seat back the head slides down after initial impact (as observed in test 

A12037). In this case, the contact between the ATD’s chin and the top of the tray table prevented the 

sliding action and resulted in significant force applied to the chin. This did not produce a high HIC value

but it did result in an upper neck tension of 893 lb which is very near the limit of 937 lb, and a very high Nij

value of 1.57, which is well over the limit.

• The lower legs translated forward in unison with the knee until the knee contacted the seatback without 

generating significant femur compression. The lower legs then flailed forward allowing tibia contact with 

the aft tube of the seat frame. The angle of the lower legs and the lack of a floor reaction surface permitted 

the knee to translate downward significantly as the torso as pelvis rotated forward. The calculated tibia 

indices for the right leg were higher than in test A13002 (which had a smaller, 30 in, seat pitch) while the 

tibia indices for the left leg were nearly identical to test A13002. All calculated tibia indices did not exceed 

the criteria limit.
A13

Braced position with arms at side of legs, energy absorbing seat back, legs back

(Figures A36 to A38)

Figure A36 – A13011 T=0 ms

Figure A37 – A13011T =120 ms

Figure A38 – A13011 T=200 ms

• The ATD is positioned with the torso forward and head against the seat back. The hands are down at the 

side of the legs, and the legs are back as far as allowed by the baggage bar.

• As the ATD and seat back moved forward, the head remained in contact with the seat back. The arms 

contacted the bottom of the seat back and seat frame but did not appear to influence the motion of the seat 

back. This interaction produced a very low HIC of 224 and all the other recorded values were below the 

criteria limits.

• The right foot did not slide forward and the left foot slid forward until the lower leg was nearly vertical. 

The knees translated forward and contacted the seat back without generating significant femur 

compression. As the torso and pelvis rotated forward, a positive Y-axis moment was generated in the right 

and left femurs but both were relatively low. 
A14

Braced position with arms at side of legs, full break-over seat back, legs back 

(Figures A39 to A41)

Figure A39 – A13012 T=0 ms

Figure A40 – A13012 T=120 ms

Figure A41 – A13012 T=180 ms

• The ATD is positioned with the torso forward and head against the seat back. The hands are down at the 

side of the legs, and the legs are back as far as allowed by the baggage bar.

• The ATD head initially remained in contact with the seat back as it folded forward. After the ATD torso 

reached about a 45 degree angle, the seat back rotated away from the ATD and the head impacted the seat 

back below the tray table. The arms contacted the bottom of the seat back and seat frame but did not appear 

to influence the motion of the seat back. Since the head and seat back moved in unison for much of the test, 

there was less time after the seat back moved away to generate relative velocity. This reduced impact 

velocity produced a very low HIC of 408 and all the other recorded values were below the criteria limits.

• The right foot did not slide forward and the left foot slid forward until the lower leg was nearly vertical. 

The knees translated forward and contacted the seat back without generating significant femur 

compression. As the torso and pelvis rotated forward, a positive Y-axis moment was generated in the right 

and left femurs but both were relatively low. 
A15

Braced position with arms at side of legs, locked out seat back, legs back

(Figures A42 to A44)

Figure A42 – A13013 T=0 ms

Figure A43 – A13013 T=120 ms

Figure A44 – A13013 T=170 ms

• The ATD is position with the torso forward and head against the seat back. The hands are down at the side 

of the legs, and the legs are back as far as allowed by the baggage bar.

• As the ATD and seat back moved forward, the head remained in contact with the seat back. The arms 

contacted the bottom of the seat back and seat frame but did not appear to influence the motion of the seat 

back. This interaction produced a very low HIC of 167, and all the other recorded values were below the 

criteria.

• The right foot did not slide forward and the left foot slid forward until the lower leg was nearly vertical. 

The knees translated forward and contacted the seat back without generating significant femur 

compression. As the torso and pelvis rotated forward, a positive Y-axis moment was generated in the right 

and left femurs but both were relatively low.
A16

Pike position with arms down at sides, legs back, rigidly supported fiberglass faced, Nomex® honeycomb wall 

(Figures A45 to A47)

Figure A45 – A13014 T=0 ms

Figure A46 – A13014 T=90 ms

Figure A47 – A13014 T=130 ms

• The ATD is positioned with the torso as far forward as it can go with the abdominal insert removed. This 

position aligns the neck with the horizontal impact vector. The hands are down at the side of the legs and 

the legs back as far as were allowed by the baggage bar. A 1.0 in thick fiberglass faced Nomex®

honeycomb panel, rigidly supported by a 0.5 in thick aluminum plate, was positioned 35 inches from the 

SRP.

• The ATD slid forward in the seat until the top of the head contacted the wall. The rest of the body 

continued to translate forward, compressing the neck visibly. The ATD hit the wall with the neck almost 

perfectly horizontal (a worst case condition for neck compressive loads). The Nij value was 2.02 and the 

upper neck compressive force was 2,399 lb, both of which are over twice the criteria limits of 1.0 and 899 

lb, respectively. However, the HIC was only 211 due to the very low impact velocity. 

• The right foot did not slide forward and the left foot slid forward until the lower leg was nearly vertical. 

The knees translated forward but did not contact the wall. Y-axis moment in both legs was relatively low.

This is likely because the torso was initially flexed forward, reducing the tendency for the pelvis to rotate 

forward during impact and in-turn induce the femur bending. 
A17

Pike position with arms down at sides, legs back, rigidly supported fiberglass faced, Nomex® honeycomb 

wall, and y-belt type restraint

(Figures A48 to A50)

Figure A48 – A13015 T=0 ms

Figure A49 – A13015 T=90 ms

Figure A50 – A13015 T=120 ms

• The ATD is positioned with the torso as far forwards as it can go with the abdominal insert removed. This 

position aligns the neck with the horizontal impact vector. The hands are down at the side of the legs and 

the legs back as far as were allowed by the baggage bar. A 1.0 in thick fiberglass faced Nomex® 

honeycomb panel, rigidly supported by a 0.5 in thick aluminum plate, was positioned 35 in from the seat

reference point. The seat belt was a y-belt of the type typically used in front row applications to limit 

forward translation of the occupant.

• The y-belt effectively limited the occupant horizontal head excursion to five inches from the initial 

position, which did not allow the ATD to contact the wall in front.

• Neither foot slid forward and the Y-axis moment in both legs was relatively low.