Evaluation of a Head Injury 

Criteria Component Test Device

Richard L. DeWeese

David M. Moorcroft

Civil Aerospace Medical Institute

Federal Aviation Administration

Oklahoma City, OK 73125

November 2004

Final Report

This document is available to the public

through the National Technical Information

Service, Springfield, Virginia 22161.

Office of Aerospace Medicine

Washington, DC 20591

DOT/FAA/AM-04/18
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.
i

Technical Report Documentation Page 

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

DOT/FAA/AM-18 

4. Title and Subtitle 5. Report Date 

Evaluation of a Head Injury Criteria Component Test Device November 2004 

6. Performing Organization Code 

 

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

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 14. Sponsoring Agency Code 

800 Independence Ave., S.W. 

Washington, DC 20591 

15. Supplemental Notes 

This work was performed under task AM-B-03-PRS96. 

16. Abstract 

 Aircraft seats that are certified to meet the requirements of 14 CFR Parts 23.562, 25.562, 27.562 and 

29.562 must protect the occupant from serious head injury as defined by the Head Injury Criterion (HIC). 

Currently this is demonstrated during a dynamic sled test that includes a 50% male-size test dummy, the seat, 

and any surrounding aircraft structure that could be impacted by the occupant’s head. To reduce cost and 

expedite design and certification, a means of demonstrating compliance using a component-level test was 

desired. A project to develop a component test method was initiated by the FAA Technical Center’s Materials 

and Structures Branch, under contract to the National Institute for Aviation Research (NIAR) at Wichita State

University (WSU). This effort resulted in the development of the HIC Component Test Device (HCTD) as 

described in FAA report DOT/FAA/AR-02-99. The HCTD consisted of a test dummy head attached to a 

pivoted arm that is propelled in an arc by an air actuator. The device was transferred to CAMI in Dec. 2002 for 

evaluation and further development. 

 A series of sled and component tests were conducted to evaluate the HCTD’s predictability, repeatability, 

and degree of correlation with the sled tests. The device produced head impact velocity and HIC results that 

were very repeatable when impacting surfaces with consistent force/deflection properties. A relationship for 

impact velocity versus firing pressure was also developed. Several representative aircraft interior surfaces were 

tested at various head impact velocities and impact angles. These surfaces included padded rigid walls, 

unpadded composite walls and wall sections, and energy absorbing and non-energy absorbing seat backs. When 

the results for the two test methods were compared, impacts with some surfaces showed correlation and some 

did not. Impacts with padded rigid walls correlated well, while impacts with stiff walls or wall sections did not. 

Impacts with seat backs yielded mixed results with correlation being dependent on the stiffness of the area of the 

seat back being impacted. A MADYMO computer model was developed to investigate factors that could 

improve correlation. Further investigation is necessary to determine if modifications to the device could improve 

the degree of correlation. 

17. Key Words 18. Distribution Statement 

Head Injury Criterion (HIC), Component Test, 

MADYMO, Aircraft Seat Test, Simulation 

Document is available to the public through the 

National Technical Information Service, 

Springfield, Virginia 22161 

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

Unclassified Unclassified 20 

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

iii

ACKNOWLEDGMENTS

The authors gratefully acknowledge the efforts of the students and staff of the National Institute 

for Aviation Research Computational Mechanics Laboratory who assisted us with the transition of 

the HIC Component Test Device to CAMI. They made many trips to CAMI to assist with system 

setup, control software development, and computer simulations. Among those who contributed, 

our special thanks go to:

Dr. Hamid Lankarani

Gunesh Prasanna Kanetkar

Cheriyan Sony Koshy

Harishanker Nagarajan

Venkatramana Prabhala

Kendale Anant Sadanand

Lalitkumar Vasantkumar Sahare

Satish Chandra Swargam

Chandrashekhar Kalyandao Thorbole

1

EVALUATION OF A HEAD INJURY CRITERIA COMPONENT TEST DEVICE

INTRODUCTION

Aircraftseatsthat are certifiedtomeettherequirements 

ofTitle14oftheCodeofFederalRegulations(CFR)Parts 

23.562, 25.562, 27.562 and 29.562 (1) must protect the 

occupantfromserious head injury as defined by the Head 

Injury Criterion (HIC). Currently this is demonstrated 

during a dynamic sled test that includes a 50% male-size 

test dummy, theseat, and any surrounding aircraft structure that could be impacted by the occupant’s head. A 

means of demonstrating compliance using a componentlevel test to reducerequirements for dynamic sled testing 

was desired. The objective of component-level testing 

was to reduce the cost of demonstrating compliance, 

provide seat manufacturers a method to expedite design 

and testing of HIC-related factors prior to certification, 

and provide data to support approval for certification. 

Component-level testing could also be used to develop 

material and structuresspecificationsforitemsthat affect 

the HIC results.

Background

A project to develop a component test method was 

initiated by the Federal Aviation Administration (FAA) 

TechnicalCenter,Materials andStructuresBranch,under 

contract to the National Institute for Aviation Research 

(NIAR) at Wichita State University (WSU). Results of 

that development effort are provided in FAA Report 

DOT/FAA/AR-02-99 (2). To determine if the device 

developed by the NIAR could effectively demonstrate 

compliance with FAA Regulations, the device was transferred to CAMI in Dec. 2002 for evaluation and further 

development.

System Description

Figure 1 shows the HIC Component Test Device 

(HCTD) as it was configured for the evaluation tests 

described in this report. The impact arm consists of a 

Hybrid II Anthropomorphic Test Dummy (ATD) head 

mounted to an arm that is pivoted at the opposite end. 

Unlike the test dummy that has a flexible, rubber neck, 

the HCTD neck connecting the head to the pivoting 

arm is made from rigid polycarbonate. The arm pivot is 

mounted to a block that is free to slide aft during device 

actuation. As shown in Figure 2, the mass distribution of 

the HCTD is quite different from the Hybrid II ATD. 

The dimensions and kinematics of the device are meant 

Figure 2. Mass Distribution Comparison

Figure 3. Sled Test Dimensional Parameters

Figure 1. HCTD Description
2 

to replicate a 50% male-size ATD restrained by a lap 

belt during a forward-facing sled test. Figure 3 illustrates 

the pertinent dimensional parameters corresponding to 

the sled tests, and Figure 4 illustrates the parameters for 

the HCTD.

The following sequence of events occur during device 

operation:

1. Prior to each test, the accumulator is slowly charged 

to the required pressure with nitrogen.

2. When the test begins, a valve is quickly opened, allowing the nitrogen stored in the accumulator tank 

to flow to the air cylinder.

3. The air cylinder in turn actuates a linkage that pushes 

the arm forward so that the head travels in an arc.

4. When the air cylinder reaches the end of its travel, 

the actuation linkage stops.

5. The head continues to travel in an arc at near-constant 

speed until it impacts the surface being tested.

The head velocity is a function of the initial accumulator pressure. A rotational potentiometer was installed to 

allow real-time motion of the pivoting arm to be recorded. 

Since the head is rigidly fixed to the pivoting arm, head 

position and velocity can be derived from this recorded 

arm angle. However, to determine the head center of 

gravity (CG) position and velocity more accurately, 

photometric analysis was also used. Test operation is 

controlled by a Labview (National Instruments, Austin, 

Texas) program that charges the accumulator, opens the 

firing valve, monitors the arm rotation, and triggers the 

data acquisition system and high-speed cameras. A schematic of the system is shown in Figure 5.

An operational problem previously noted by NIAR 

was that the air cylinder was still accelerating the device 

arm as it contacted the test specimen, and the arm would 

contact the actuator linkage during rebound. Ideally, the 

arm should be freely coasting throughout the impact. 

This was corrected by moving the actuator linkage and 

air cylinder aft providing the necessary clearance to 

eliminate the problem. 

Predictability and Repeatability Tests

An initial series of tests were accomplished to determine 

if the device could produce impact velocities that were 

both predictable and repeatable. A measure of repeatability 

for head acceleration responses was also desired.

Thin Aluminum Sheets. The first impact surface 

evaluated, a 2024-T3 aluminum sheet, was 28.5” W x 

31” H x 0.063” T. It was bolted at the vertical edges to 

4-inch-wide aluminum C-channels that were, in turn, 

bolted to a rigid support. This impact surface had been 

devised by NIAR for development purposes only and 

was not meant to represent any actual aircraft interior 

surface. When impacted in the center, the aluminum 

sheet bowed forward and the C-channel supports flexed 

inward. Our test results are compared with the NIAR 

results in Table 1. This table shows the accumulator 

pressure, head velocity, impact angle, and HIC results 

of two tests conducted by NIAR and three conducted 

by CAMI using this surface. CAMI’s HIC results for this 

surface varied widely and differed significantly from the 

NIAR results. It was determined that the performance of 

this impact surface is very sensitive to installation details. 

Since the aluminum support channels were deforming 

plastically during each test, each new aluminum sheet 

installed had to be match drilled to fit to get consistent 

boundary conditions. Achieving a precise fit along each 

edge was not considered a practical solution and would 

still not address the progressive permanent deformation 

of the support channels that could also be contributing 

to the inconsistent performance. 

Figure 4. HCTD Dimensional Parameters

���������������������������
3

Polyethylene Foam Padding. For this initial series 

of tests, a simple surface that would provide consistent 

HIC results was needed in order to evaluate the HCTD’s 

repeatability. A 4.5”-thick stack of 1.6 lb/cu ft density 

polyethylene flotation foam, covered with 0.5” of soft 

polyurethane foam, was chosen to meet this need. The 

foam stack was taped to a smooth, rigid wall, but the foam 

sheets comprising the stack were not bonded together or 

to the wall. When impacted, the foam compressed and 

slipped downward somewhat. The test results for this 

surface are also provided in Table 1. This table summarizes 

eight tests conducted at accumulator pressures of 40, 

80, 150, and 225 PSI. The performance of this impact 

surface was very consistent and produced a predictable 

relationship between impact velocity and HIC, as shown 

in Figure 6. Also, the low HIC results provided by these 

foam pads were somewhat surprising since other resilient 

foams previously tested had performed poorly. (3) The 

pad’s freedom to slide vertically during the impact appears 

to contribute significantly to reducing HIC values.

Repeatability Results. Some of the polyethylene foam 

pad tests and several of the tests accomplished later in the 

program were repeated at various accumulator pressures 

to determine if the device could produce repeatable velocities. Three tests were accomplished at approximately 

150 PSI, five at 200 PSI, three at 225 PSI, and nine at 

262 PSI. These repeated tests are summarized in Table 2, 

which provides the velocity, average velocity and velocity variation for each pressure. At 262 PSI (the pressure 

range used to replicate head impacts with seatbacks), 

the demonstrated repeatability for 50.7 ft/s velocity was 

± 1.2 ft/s. The repeatability of the head acceleration 

response was determined from two identical tests using 

the polyethylene foam pad (H03-311 and H03-312). 

At the 43.6 ft/s impact velocity achieved for these tests, 

the average HIC value was 1109, and the variation was 

± 25. Overall, the repeatability of the device relative to 

head velocity and HIC was deemed to be sufficient for 

the intended purpose.

PredictabilityResults. The results of these preliminary 

tests were used to derive the accumulator pressure versus 

head CG velocity relationship. As testing continued, it 

was determined that a change in the initial position of 

the pivot point would increase the mechanical advantage 

of the air cylinder, thus allowing higher velocities to be 

generated. Figure 7 shows the pressure vs. velocity relationship derived for both the initial and improved geometries. While a clear trend exists, the data spread tends to 

increase with pressure. This relationship was continually 

revised as more tests were accomplished, but the degree 

of uncertainty did not improve. Fortunately, the device’s 

good velocity repeatability enables us to overcome the 

less-than-optimum predictability. In practice, “trial runs” 

can be done to dial in the desired velocity before placing 

the item to be struck in front of the device.

Impact Tests of Representative Aircraft Interior 

Surfaces

A series of sled tests and HCTD tests were accomplished 

to determine the HCTD’s performance when impacting 

typical aircraft interior surfaces. These tests evaluated the 

HCTD’s performance over the range of contact areas, 

head impact velocities, and impact angles that could be 

encountered during certification tests involving realistic 

Table 1. Initial Tests

Surface Test ID

Pressure 

PSI

Head Vel. 

Ft/Sec

Impact Angle 

Degrees HIC

HIC Duration 

Milliseconds

Avg. Accel 

During HIC 

G's

Thin Aluminum Sheets (NIAR) 01057-24 150 40.9 37.0 763.0 21 67.0

(NIAR) 01057-28 140 40.0 39.0 752.0 25 62.2

H03-302 140 38.2 43.0 2652.0 16 121.0

H03-303 140 36.5 43.0 911.0 22 69.3

H03-304 133 35.2 43.0 2227.0 18 109.0

Polyethylene H03-305 40 19.8 43.0 102.6 25 27.5

Foam Padding H03-308 40 18.0 43.0 105.0 18 27.0

H03-306 80 29.2 43.0 329.4 21 47.6

H03-309 80 28.8 43.0 413.7 19 53.0

H03-307 150 37.2 43.0 735.5 14 66.3

H03-310 150 39.6 43.0 739.6 21 65.0

H03-311 225 43.6 43.0 1133.5 24 73.8

H03-312 225 43.6 43.0 1084.0 25 71.1
4 

HIC vs Velocity (4.5" Polyethylene Pad)

y = 0.0192x2.8977

R2 = 0.9954

0

200

400

600

800

1000

1200

1400

0 5 10 15 20 25 30 35 40 45 50 55 60

Head Impact Velocity (ft/sec)

HIC

Figure 6. HIC vs. Head Impact Velocity

Table 2. Velocity Repeatability Tests 

Test # Geometry

Pressure 

PSI

Velocity 

Ft/Sec

Avg. 

Ft/Sec

Variation 

Ft/Sec

H03-307 Initial 150 37.2

H03-310 Initial 150 39.6 37.9 1.4

H03-314 Initial 148 36.9

H03-315 Initial 200 40.3

H03-317 Initial 200 39.5

H03-318 Initial 200 39.0 39.2 1.3

H03-319 Initial 200 39.3

H03-325 Initial 200 37.7

H03-328 Final 225 47.0

H03-329 Final 225 45.8 46.0 0.9

H03-333 Final 225 45.2

H04-301 Final 262 51.3

H04-302 Final 262 50.6

H04-303 Final 262 50.8

H04-304 Final 262 51.5 50.7 1.2

H04-305 Final 262 51.6

H04-306 Final 262 50.5

H04-307 Final 262 51.0

H04-308 Final 262 50.0

H04-309 Final 262 49.2
5

surfaces. It was expected that for these surfaces, the critical parameters of head impact velocity, impact angle, and 

point of contact would significantly affect the magnitude 

of the head accelerations measured. In dynamic impact 

tests, these critical parameters are dependent on the sled 

velocity, sled deceleration pulse, and the position of the 

surface with respect to the sled occupant. To allow determination of a deceleration profile and impact surface 

position that would produce the critical parameters desired, a MADYMO (TNO, The Netherlands) computer 

model was developed to predict occupant kinematics. Use 

of the model greatly reduced the number of trial runs 

that otherwise would have been necessary.

The sled tests utilized a rigid seat with a lap belt restrained Hybrid II, 50%-size ATD. The head velocity, 

impact angle, and point of impact on the evaluation 

surface were derived from the high-speed video of each 

sled test using the photometric analysis procedures found 

in SAE ARP 5725 (4). For the corresponding HCTD 

tests, the relative position between the HCTD and the 

evaluation surface, as well as the accumulator pressure, 

was set to reproduce these critical values as closely as 

practical. Table 3 summarizes the results of this test series. 

This table provides a comparison of the HCTD and sled 

tests, showing the head velocity, head impact angle, and 

the HIC and HIC duration for various aircraft interior 

surfaces described as follows:

Polyethylene Foam Pad. To represent a heavily padded interior wall, a 4”-thick block of 1.7 lb/cu ft density, 

polyethylene foam was taped to a smooth, rigid wall, as 

shown in Figure 8. During the head impact, the foam 

block was compressed and slid down the wall. As with the 

foam used in the initial tests, the impact results showed 

good repeatability.

Fiberglass-Faced, Aluminum Honeycomb. To represent a section of a galley wall with interior bracing, a 

24’ W x 24” H x 1” T piece of fiberglass-faced, 3/8”-cell 

aluminum honeycomb was supported along all four 

edges by a rigid frame, as shown in Figure 9. NIAR had 

evaluated 48” W x 48” H x 1” T panels of this material 

(referred to as Series III) in a previous study (5). The 

frame’s interior dimensions were 20” W x 19.5” H. The 

panel was clamped along the top edge and supported 

along the bottom to prevent it from slipping. When 

struck, the panel dented significantly in the center. As 

expected, the amount of deformation increased as the 

head impact velocity increased.

Narrow, Fiberglass Faced, Nomex Honeycomb 

Panels. To represent a small closet wall, a 24” W x 48” 

H x 1” T piece of fiberglass-faced, 1/8”-cell Nomex honeycomb was clamped along the top and bottom edges, as 

showninFigure10.Thewallfacewas carpeted.NIARhad 

evaluated 48” W x 48” H x 1” T panels of this material 

(referred to as Series II) in a previous study (5). When 

Figure 7. Pressure vs. Head Impact Velocity 

Accumulator Pressure vs Head Velocity

y = 8.6351e0.0788x

R2 = 0.9432

y = 8.5959e0.069x

R2 = 0.9774

0

50

100

150

200

250

300

350

0 5 10 15 20 25 30 35 40 45 50 55 60

Velocity (ft/sec)

Pressure (PSI)

Initial Geometry Final Geometry Initial Trend Final Trend
6 

Table 3. Aircraft Interior Surface Tests 

Surface Test ID

Head Vel. 

Ft/Sec

Impact Angle 

Degrees HIC

HIC Duration 

Milliseconds

Polyethylene Foam Pad A03007 32.2 45.7 304.3 28

A03008 32.6 46.7 302.1 29

H03316 28.3 43.0 400.8 19

A03011 38.7 40.6 667.9 17

A03013 38.7 40.6 699.1 21

H03314 36.9 43.0 756.3 18

A03009 42.4 41.6 1047.2 16

A03010 43.8 42.9 1044.5 16

H03315 40.3 43.0 918.9 23

H03317 39.5 43.0 942.6 15

H03318 39.0 43.0 873.6 17

H03319 39.3 43.0 923.3 17

Fiberglass Faced, Aluminum Honeycomb A03022 42.1 42.4 772.8 20

H03322 41.9 42.4 726.7 26

A03023 46.3 38.4 1009.8 21

H03329 45.8 37.9 802.5 26

Narrow, Fiberglass Faced, Nomex Honeycomb Panel A03015 38.0 44.6 1110.0 17

A03018 37.9 44.1 944.4 16

H03325 37.7 44.9 389.1 5

Wide, Fiberglass Faced, Nomex Honeycomb Panel A03004 44.7 53.2 1084.3 7

H03320 47.6 53.0 1420.6 23

Narrow-Body Class Divider Panel A03028 41.6 43.8 458.2 34

H03330 41.6 44.0 285.7 36

Wide-Body Class Divider Panel A03027 40.5 45.8 1547.4 5

A03034 41.3 49.5 1597.8 11

H03331 40.8 44.0 670.6 9

EA Seat Back A03030 48.6 30.6 639.3 30

H03332 49.0 33.3 324.5 10

EA Seat Back with Video A03032 49.2 35.2 789.4 5

H03333 45.2 37.2 752.6 6

Note: Seld Test ID numbers start with "A" HCTD Test ID numbers start with "H"
7

struck, the panel bowed in the middle, showed signs of 

delamination, but did not fracture. 

Wide, Fiberglass-Faced, Nomex Honeycomb Panels. 

To investigate the affect of attachment methods, a 48” W 

x 48” H x 1” T piece of fiberglass-faced, 1/8”-cell Nomex 

honeycomb was attached to a rigid frame at four points, 

as shown in Figure 11. The attachments had 1.625”-thick 

spacers between the wall and frame, and the wall face was 

carpeted. At the points of attachment, the honeycomb had 

been filled with an epoxy potting compound to provide 

a solid mounting surface. The attachment points were 

in a rectangular pattern spaced 24” horizontally and 45” 

vertically. This was the same material that was used for 

the previously mentioned 24” W x 48” H sample tests. 

While this mounting method was not representative of 

any actual aircraft installation, it was included to determine the affect that boundary conditions have on impact 

performance. When struck, the wall bowed horizontally 

until it contacted the support frame, which was 1.625 

inches away from the back surface. 

Class Divider Panels. Class divider panels from 

narrow-body and wide-body aircraft were mounted in a 

fashion emulating the location and stiffness of a typical 

aircraft installation. The narrow-body panel was made 

from 1”-thick fiberglass faced, Nomex honeycomb and 

was attached at the top and bottom to legs that were free 

to pivot and lengthen as the panel bowed. Figures 12 and 

13 show the mounting method in detail. The wide-body 

panel was much taller and was also made from 1”-thick 

fiberglass-faced Nomex honeycomb. It was also attached 

using the same method but was heavier and more rigid 

since the entire periphery and attachment points had 

been “potted” in. Figure 14 shows the panel mounted to 

the rigid support frame. When the narrow-body panel 

was struck, it bowed forward until it folded in the area 

near the upper attach points. When the wide-body panel 

was struck, the panel bowed forward until it cracked 

Figure 8. Foam Pad Pre-Test Figure 9. Aluminum Honeycomb Post-Test

Figure 10. Narrow Nomex Panel

Figure 11. Wide Nomex Panel
8 

horizontally at a notch 2/3 up the panel (Figure 15). A 

second sled test of the wide-body panel was accomplished 

after the horizontal crack was repaired (we only had two 

of these valuable samples). This test was done to verify 

the very high HIC measured in the first test. Both the 

panel response and HIC for the second test were similar 

to the first test. 

Energy-Absorbing (EA) Seatback. A set of older, 

statically qualified, passenger double seats was modified 

by adding an energy-absorbing element to each seatback 

hinge mechanism. An energy absorber of this type allows 

the seatback to stroke forward when a force of approximately 300 lb. is applied horizontally at the top of the 

tray table. This stroking action can significantly reduce 

the probability of head injury. The area above the tray 

table on one set of seatbacks had a hollow cavity covered 

by a fiberglass shroud. The other set was modified by 

adding a wood block just above the tray table to emulate 

the weight and stiffness of a typical video screen installation (Figure 16).

During sled and HCTD tests of the hollow seatback, 

the head struck in the center of the seat, 3.6 inches down 

from the top of the seatback. The head shattered the fiberglass cover, allowing it to penetrate into the seatback 

cavity before pushing the entire seatback forward. During 

the sled and HCTD tests of the seatback that had the 

simulated video screen, the head struck the center of the 

seat, 5.4 inches down from the top of the seat. The head 

did not penetrate the seatback but did push the seatback 

forward significantly.

During the sled test, the top of the hollow seatback 

elastically flexed forward and then began to rebound aftward with a velocity of 8.5 ft./sec. just as the ATD stuck 

it. Figure 17 shows this point in time. The seatback with 

the video screen emulation was still flexing forward with 

a velocity of 3.4 ft./sec. when the ATD struck it (Figure 

Figure 12. Narrow-Body Class Divider Figure 13. Class Divider Mounting Detail

Figure 14. Wide-Body Class Divider

Figure 15. Wide-Body Class Divider Post-Test
9

18). To properly simulate these impacts with the HCTD, 

some means of compensating for the flexed location and 

motion of the seatbacks was needed. The seat flexure was 

emulated by simply pulling the backs forward with a strap 

to the same position as seen in the sled test. The hollow 

seatback was pulled forward 4.4 inches from nominal, 

and the seatback with the video screen emulation was 

pulled forward 12.1 inches. Since inducing the appropriate velocity to the seatbacks was not practical, the speed 

of the head impact was adjusted instead. To calculate 

the head velocity difference needed to compensate for 

seatback motion, an equivalent impact energy approach 

was taken. If the impact between the HCTD and the 

seatback is thought of as a collision between two inverted 

pendulums, then the combined rotational energy ( Iω2 ) 

of both pendulums at the time of impact should be the 

same for both the sled and component test. To derive 

the velocity change, the mass moment of inertia ( I ) was 

measured for both the HCTD arm and each seatback, 

and the angular velocity ( ω ) was calculated for each 

seatback. Since the moment of inertia for the HCTD 

arm was much greater than the seatbacks, only a small 

change in velocity was necessary to compensate for the 

significant velocity of the seatback.

Follow-on Seatback Impact Tests

After the initial series of tests were complete (predictability, repeatability, and representative interior surfaces), 

the results were examined to determine the next course of 

action. Since the results for tourist-class passenger seatbacks showed a promising correlation trend and would 

be a very useful application, a follow-on series of tests 

was conducted to establish the level of correlation that 

could be achieved by the HCTD. Two locations on the 

seatback that are typically struck during a certification 

test were chosen as impact targets. The first location was 

at a point on the seatback centerline midway between the 

top of the seat and the tray table. The second location 

was a point offset 6” to the side at the top edge of the 

tray table. Figures 19 and 20 show the chalk marks left 

by the ATD’s head at the two impact points. The seat 

used for the evaluation was a triple-place passenger seat 

with seatbacks not incorporating the dedicated energy 

absorption mechanisms that many recent designs do. 

This design, instead, relied on elastic/plastic flexing of 

the seatback frame to provide the necessary compliance. When a steadily increasing static load was applied 

horizontally at the top of the tray table, the seatback 

exhibited elastic behavior up to 500 lb of load and 11” 

of deflection, at which point the seat recline mechanism 

began to plastically deform until it completely failed at 

13.5” of deflection. A single triple-place passenger seat 

Figure 16. Video Screen Emulation 

Figure 17. Hollow Seatback Impact

Figure 18. Video in Seatback Impact
10 

frame was used for this entire test series. A new seatback 

frame, tray table, and recline mechanism were installed 

in the center seat position prior to each test. The area 

above the tray table was filled with a block of polyethylene 

foam encased in fire-blocking material. Since a limited 

number of these blocks and seat covers were available, 

they were reused unless obviously damaged. During the 

sled tests, the seatbacks exhibited the same tendency to 

flex forward prior to ATD impact, as seen in the previous test series. The increased stiffness of this seatback 

design, however, reduced the average seatback rebound 

velocities to 6.3 ft/s and the forward flexure to 2”. The 

velocity of the HCTD arm was adjusted using the same 

equivalent energy method used in the previous seatback 

tests. Table 4 summarizes the results of this test series. 

For each group of similar tests, the table provides the 

head-impact velocity, impact angle, HIC, HIC duration, 

average HIC, and the HIC variation. In addition to the 

data shown in the table, the following observations were 

made relative to the follow-on tests:

Seatback Centered. During the three sled tests, the 

ATD consistently struck in the center of the seatback - 3” 

above the tray table - then creased the center of the tray 

table, shearing off the latch in the process. The seatback 

also showed this same damage pattern during each of the 

three HCTD impacts. 

Seatback Offset. During the three sled tests, the ATD 

consistently struck 1” above the top of the tray table and 

6” to the right of center, crushing the top edge of the 

table, then shearing the hinge on that side as the head 

slid down the right side of the seatback. In two of the 

Figure 19. Center Seatback Impact Point

Figure 20. Offset Seatback Impact Point 

Table 4. Follow-on Seatback Tests 

Surface Test ID

Head Vel 

Ft/Sec

Impact Angle 

Degrees HIC

HIC Duration 

Milliseconds

Avg. 

HIC

Variation 

HIC

Seatback Centered A04075 47.4 38.5 1207.0 29

A04076 48.0 38.7 1179.4 25 1203.9 23.0

A04077 47.4 38.9 1225.4 10

H04304 51.5 40.0 819.7 12

H04305 51.6 40.0 804.6 12 814.1 7.6

H04306 50.5 40.0 818.1 12

Seatback Offset A04081 49.2 41.4 867.1 7

A04082 48.1 42.9 907.3 7 858.7 52.9

A04083 48.8 42.8 801.6 11

H04307 51.0 42.6 737.9 17

H04308 50.0 42.6 881.5 19 764.6 103.6

H04309 49.2 42.6 674.4 7

Note: Seld Test ID numbers start with "A" HCTD Test ID numbers start with "H"
11

HCTD tests, the same failure mode was seen. In one of 

the impacts, however, the tray table hinge did not shear 

off. This increased the local stiffness, resulting in higher 

head accelerations.

Correlation Results

When the results were plotted for all of the corresponding sled and HCTD tests accomplished during 

CAMI’s evaluation (including previous tests of various 

interior surfaces and the latest seatback tests), no clear 

correlation trend emerged (Figure 21). The degree of correlation varied significantly between the various surfaces 

impacted. The only discernable trend is that the correlation seemed to decrease as the stiffness of the surface 

being stuck increased. If correlation trends existed for 

clear-cut categories of surfaces such as class dividers or 

seatbacks, deriving a transfer function for each category 

could compensate for this effect. Unfortunately, as seen 

in the follow-on seatback impact tests, different results 

can be achieved when striking different parts of the same 

item, making this categorization difficult. NHTSA developed a component test device called the Free Motion 

Headform (FMH), and they were able to derive a linear 

transfer function and achieve an r2 value (a standard 

goodness of fit measurement) of 0.97 (6). The NHTSA 

test data are plotted in Figure 22, which shows a clear 

trend between the sled and component test. One possible 

reason for the high degree of correlation achieved by the 

NHTSA may be that the surfaces the device was designed 

to evaluate were all very simple and similar (1” of padding on relatively stiff structure). In its current stage of 

development, however, the HCTD does not provide a 

similar level of confidence in its output when used with 

complex impact surfaces. 

DISCUSSION

Factors Affecting Correlation. The neck flexibility 

and mass distribution of the HCTD is significantly different from the Hybrid II ATD used in the sled tests. 

This causes the head interaction with the impact surface 

to differ as well. In most sled tests involving impacts onto 

vertical surfaces, the ATD’s neck flexed rearward during the 

period of head contact with the surface. This allowed the 

head to rotate rearward as it was pushed down the surface 

by the momentum of the ATD’s torso. Since the neck of 

the HCTD cannot flex, and its torso is much lighter, the 

headform tended to not travel down the surface as far 

and the headform would rebound horizontally after the 

initial impact. Figure 23 shows the difference in head path 

for a typical set of corresponding tests. This difference in 

kinematics (after the contact with the impact surface) may 

be one cause for the lack of correlation between the two 

test methods. Since current research indicates that rapid 

head rotations are a potential source of brain injury (7), 

the inability of the device in its current form to replicate 

Civil Aerospace Medical Institute Comparison

FULL ATD vs HCTD HIC

0

500

1000

1500

2000

0 500 1000 1500 2000

HCTD HIC

FULL ATD HIC

Full Panel

Pad

Narrow Panel

AL Honeycomb

Class Divider

EA Seat Back

Center Seat Back

Offset Seat Back

`

Figure 21. Full ATD HIC vs HCTD HIC
12 

Figure 22. Full ATD HIC vs FMH HIC

National Highway Traffic Safety Administration Comparison

FULL ATD vs FMH HIC

y = 0.7545x + 166.38

R2

 = 0.9689

0

500

1000

1500

2000

2500

3000

0 500 1000 1500 2000 2500 3000

FMH HIC 

FULL ATD HIC

`

Figure 23. Head Path Comparison 

Head Path Comparison (Class Divider)

0

5

10

15

20

25

30

35

-5 0 5 10 15 20 25 30 35 40

X Displacement (Inches)

Z Displacement (Inches)

A03028 H03330

HCTD

Sled Test

Impact 

Point
13

this kinematic would limit its usefulness in measuring 

advanced injury assessment parameters.

The ability of the HCTD to duplicate the critical 

parameters of impact velocity and impact angle was limited by the practical constraints of velocity repeatability, 

impact angle adjustment increment, and the amount of 

laboratory time that could be spent repeating tests in an 

attempt to achieve the desired parameters. Therefore, 

some of the “corresponding” sled and HCTD tests shown 

in Table 3 had differences in these critical parameters. 

Since HIC is directly related to impact velocity (Figure 

6), it is reasonable to assume that the differences could 

affect the results somewhat. If the HCTD test velocities 

had matched the velocity goals for all of the tests, the 

level of correlation might have improved for some tests, 

and decreased for others. Since the tests that had good 

velocity agreement also showed the least correlation, it 

is unlikely that the overall correlation for all cases would 

have changed significantly.

Validation Criteria Development. One of the factors 

needed to determine the appropriate validation criteria 

for a device like the HCTD is the data spread of the sled 

tests being emulated. If the component test device results 

fell within this data spread, then its accuracy in measuring HIC would be equivalent to the sled test. This high 

level of correlation, however, might not be necessary for 

a device to be useful. Since the sled tests in this study 

were carefully conducted so as to maximize repeatability, 

the results may represent the smallest data spread that 

could reasonably be achieved in a typical certification 

test. Table 5 provides a summary of the sled tests repeated 

during this study. As can be seen, the degree of HIC 

repeatability is directly related to the complexity of the 

item being struck. Simple items (like foam pads) had a 

very small amount of variation, while complex items (like 

seatbacks or composite wall panels) showed significant 

spread in the data. This could be due to slight material 

and manufacturing variations or small differences in the 

point of impact with non-homogeneous surfaces. As was 

observed during seatback tests, even small variations in 

impact point can produce a very different response. For 

example, in one of two otherwise identical tests, the tray 

table crushed, instead of shearing off. Manufacturers of 

aircraft interior items may want to take this natural variability into account to ensure that items falling at the 

extremes of the variation would still meet the required 

HIC limit. The small amount of variation in the foam 

pad tests, however, illustrates that HIC measurements 

from sled tests can be very repeatable.

Evaluation of Potential Modifications

A MADYMO model of the current HCTD configuration was developed to evaluate potential design changes 

for the HCTD. Impacts into a polyethylene foam covered rigid wall were simulated. This surface was chosen 

because it had been evaluated extensively during the test 

program and had yielded repeatable results for both the 

sled and component tests. The model was calibrated using 

Table 5. Sled Test HIC Repeatability 

Surface Test ID

Sled Vel. 

Ft/sec

Sled Accel 

G's

Head Vel. 

Ft/Sec

Impact Angle 

Degrees HIC

HIC Duration 

Milliseconds

HIC 

Avg.

HIC 

Variation

Polyethylene Foam Pad A03007 23.0 8.9 32.2 45.7 304.3 28 303.2 1.1

A03008 23.0 8.9 32.6 46.7 302.1 29

A03011 29.1 10.5 38.7 40.6 667.9 17 683.5 15.6

A03013 29.1 10.6 38.7 40.6 699.1 21

A03009 32.4 11.8 42.4 41.6 1047.2 16 1045.9 1.4

A03010 34.1 11.8 43.8 42.9 1044.5 16

Narrow, Fiberglass Faced, A03015 29.7 10.4 38.0 44.6 1110.0 17 1027.2 82.8

Nomex Honeycomb Panel A03018 29.1 9.7 37.9 44.1 944.4 16

Wide-Body Class Divider A03027 30.6 11.2 40.5 45.8 1547.4 5 1572.6 25.2

A03034 30.6 11.5 41.3 49.5 1597.8 11

Seatback Centered A04075 44.6 16.3 47.4 38.5 1207.0 29 1203.9 23.0

A04076 44.5 16.4 48.0 38.7 1179.4 25

A04077 44.5 16.1 47.4 38.9 1225.4 10

Seatback Offset A04081 44.7 16.6 49.2 41.4 867.1 7 858.7 52.9

A04082 44.7 16.5 48.1 42.9 907.3 7

A04083 44.8 16.6 48.8 42.8 801.6 11
14 

Figure 24. Foam Properties 

Polyethylene Foam Material Properties

0.00

50.00

100.00

150.00

200.00

250.00

0 10 20 30 40 50 60 70 80 90 100

Strain (%)

Stress (PSI)

Flat Platen (2 in/min) Madymo Input Hemispherical Platen (2 in/min)

Note: Only Loading Portion of

 Curves Shown For Clarity 

Table 6. Simulation Results

HIC HIC HIC

Duration Pad Slip Duration Pad Slip Duration Pad Slip

Designator Configuration HIC (ms) (inches) HIC (ms) (inches) HIC (ms) (inches)

HCTD Test (Range) 401 19.4 1.3 756 17.5 1.3 874-943 15.0-22.6 1.6-3.1

Baseline Light - Rigid Neck 399 15.7 0.9 735 18.0 1.6 937 16.4 1.8

1 Light - Flex Neck Orientation 1 420 17.4 0.1 880 16.7 0.0 907 17.5 0.9

2 Light - Flex Neck Orinetation 2 480 16.0 0.0 762 16.4 1.2 920 16.2 1.4

3 Heavy - Rigid Neck 198 25.4 1.9 off scale 0.4 0.1 off scale 0.5 0.1

4 Heavy - Flex Neck Orientation 1 395 22.6 0.1 810 19.0 1.3 1063 20.9 0.9

5 Heavy - Flex Neck Orientation 2 500 18.9 0.0 812 18.7 1.2 981 18.7 1.6

Sled Test (Range) 302-304 27.9-28.7 1.9-2.1 668-699 17.1-20.7 1.3-1.8 1046-1047 15.9-16.0 1.0-1.3

Modeled Test Condtion Corresponding HCTD Test Corresponding Sled Test

28.3 Ft/Sec, 43 degree angle

36.9 Ft/Sec, 43 degree angle

39.5 Ft/Sec, 43 degree angle

Model Parametric

Rigid Neck Rigid Polycarbonate neck

FlexNeck Standard test dummy rubber neck

Light configuration

Heavy configuration

Orientation 1

Orientation 2

28.3 Ft/Sec Impact Vel. 36.9 Ft/ Sec Impact Vel. 39.5 Ft/Sec Impact Vel.

H03315 & H03317-19

H03314

H03316 A03007 & A 03008

A03011 & A 03013

A03009 & A 03010

Dummy Head Orientation: -30 degrees from horizontal

Description

42.5 lb. total system weight

138.8 lb. total system weight

HCTD Head Orientation: -50 degrees from horizontal
15

an intermediate speed test, then validated using higher 

and lower speed tests. The model was used to evaluate 

the effect of neck stiffness and system mass. 

Model Description. The HCTD model consists of 

a Hybrid II 50th percentile ATD head-neck complex 

attached to a rigid arm that is, in turn, pivoted from a 

translating rigid base. The head-neck complex is locked 

to the pendulum arm through a joint at the neck bracket. 

The head-neck complex also contains two joints to allow 

neck flexion. For the baseline model, both neck joints 

are locked at their nominal positions. A revolute joint is 

defined between the base and the pendulum arm to allow 

rotation in the x-z plane (a vertical plane aligned in the 

longitudinal direction). A translational joint is defined at 

the base to allow motion in the aft x-direction (longitudinal 

direction). The resultant length between the head CG 

and the pivot is 27.6”. For the baseline configuration, 

the base weighs 20.5 lb, the arm weighs 7.0 lb., and the 

head-neck complex weighs 15 lb. 

The impact surface for this series of simulations is a 

polyethylene foam covered wall. The wall is modeled as 

a rigid plane. The foam was modeled as a finite element 

solid, 12.5” W x 18” H x 4” T. The density of the foam 

is 1.5 lb/ft3, which results in a weight of 0.78 lb. The 

front face of the foam is 23.35” in front of the arm pivot 

point. At this setback distance, the head impact angle is 

43°. The stress/strain properties chosen for the foam are 

shown in Figure 24. The coefficient of friction between 

the head and the foam was 0.50. The coefficient of friction between the foam and the wall was 0.54. To simulate 

the transition between static and sliding coefficients of 

friction, the foam was held in place by a free joint set to 

unlock when 495 lb. of vertical force is applied to the 

foam block. 

Calibration and Validation. During all of the tests 

with foam-covered walls, the head compressed the foam 

and then forced the entire pad to slip down the wall 

somewhat. Therefore, to accurately model the interaction 

between the head and the wall, it was important to not 

only match the head acceleration but also the device and 

impact surface kinematics. The model was calibrated by 

adjusting the input parameters (within normal ranges) 

such that the head acceleration, foam z motion, foam x 

deformation, and HCTD base x motion replicated test 

H03314. Since the dynamic force-deflection properties 

of the foam were unknown, its properties were essentially 

derived during the calibration process. As seen in Figure 24, the derived dynamic response is softer than the 

static response measured with a flat platen but generally 

stiffer than the response derived from static tests with 

a hemispherical platen. Use of this unique stress/strain 

response was necessary to compensate for rate effects and 

the finite element model’s limitations in reproducing the 

constitutive properties of foam material. The model was 

validated by comparing results from higher and lower 

impact velocity simulations with the corresponding tests 

(H03315 and H03316). 

Model Use. The two main factors evaluated to determine the potential for better correlation between the 

HCTD and a full sled test were neck flexion and system 

weight. Each was evaluated separately and then combined 

to produce six model configurations. To model a flexible 

neck, the head-neck complex from the MADYMO Hybrid II dummy was unlocked. The neck consists of two 

joints, with joint resistance properties unchanged from the 

complete dummy. The flexible neck model was simulated 

in two configurations, first with the neck in the un-flexed 

state such that at impact, the head orientation matched 

that of the component test with a rigid neck, and second 

in a pre-flexed configuration such that the head orientation matched that of the sled test. To evaluate the affect 

of system mass, the mass of the pendulum arm and base 

was increased to match the effective weight of the torso 

and pelvis of the ATD. The pendulum arm weight was 

increased from 7 lb. to 51.1 lb. The center of gravity of 

the arm was also moved from 10.6” to 15.3” above the 

pivot. The base weight was increased from 20.5 lb to 

72.7 lb. Each factor was simulated for the three impact 

velocities mentioned earlier.

Computer Simulation Results. The results of the 

parametric study are presented in Table 6. None of the 

configurations showed an improvement over the baseline 

for all three velocities. Conversely, only configuration 3 

(heavy with a rigid neck) had a definite negative effect 

on correlation for any of the three velocities. Further 

examination of the data reveals a clear relationship between the vertical pad excursion (pad slip) and HIC. 

Regardless of configuration, when the pad slipped less 

than the baseline, the HIC went up and vice versa. For 

this impact surface, vertical sliding is an important part 

of its overall force/deflection response to impact. The 

modifications that increased the normal force and/or 

reduced the vertical force on the pad (thus reducing pad 

vertical excursion) tended to result in higher HIC values. 

While this modeling exercise did not favor a particular 

configuration, it did reveal the complex nature of the 

interaction between the HCTD and the impact surface. 

If models are developed for the surfaces that did not correlate as well as the foam pads, then any improvement 

trends should become clearer.
16

CONCLUSIONS

At its current stage of development, the HCTD does 

not produce results that correlate with similar full-scale 

sled tests in all cases. Further investigation is necessary to 

determine if modifications to the HCTD can improve its 

degree of correlation with sled tests of actual aircraft components. While a single test device that can successfully 

emulate impacts with the wide variety of surfaces found 

in commercial transport aircraft would be advantageous, 

narrowing the focus of the device’s usage may be necessary 

to achieve a useful level of correlation. If modifications 

are done, then the modified configuration will need to 

be extensively tested to validate its performance.

REFERENCES

1. Code of Federal Regulations, Title 14, Parts 23.562, 

25.562, 27.562 and 29.562. Washington DC: US 

Government Printing Office.

2. Lankarani H. Development of a Component 

Head Injury Criteria (HIC) Tester for Aircraft Seat 

Certification. Washington, DC: Department of 

Transportation/Federal Aviation Administration; 

2002, Nov. FAA report no. DOT/FAA/AR-02-99.

3. Gowdy V. Evaluation of the Instrumented Ball Impact Procedure to Assess Head Impact Protection 

in Airplanes; 1995, May. SAE Report 951166.

4. SAE International. Photometric Data Acquisition 

Procedures for Impact Test: 2003, Jun. Aerospace 

Recommended Practice 5725

5. Lankarani H. Design and Fabrication of a HeadInjury-Criteria Compliant Bulkhead. Washington, 

DC: Department of Transportation/Federal Aviation Administration; 2002, Dec. FAA report no. 

DOT/FAA/AR-02-98. 

6. Willke D. Upper Interior Head Protection, Volume II: Fleet Characterization and Countermeasure Evaluation. Washington, DC: Department of 

Transportation/National Highway Traffic Safety 

Administration; 1991, Nov. NHTSA report DOT 

HS 807 866.

7. Takhonts EG, Eppinger RH, et. al., On the Development of the SIMon Finite Element Head 

Model, Stapp Car Crash Journal; 2003, Oct. 47:

107-133.