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BODY SIZE ACCOMMODATION IN USAF AIRCRAFT

Gregory F. Zehner

Human Effectiveness Directorate
Crew System Interface Division
Wright-Patterson AFB, OH 45433-7022

Jeffrey A. Hudson

Sytronics, Inc.
4433 Dayton-Xenia Road
Dayton, OH 45432

Technical Report AFRL-HE-WP-TR-2002-0118
United States Air Force Research Laboratory
Wright-Patterson AFB, OH

January 20

ABSTRACT

"The USAF is considering relaxing body size entrance requirements for Undergraduate Pilot Training (AFI 48-123 [Air Force Instruction 48-123, Medical Examinations and Standards, 22 May 2001]) to provide equal opportunity for both genders. The research described here was undertaken from 1997 through 2000 to determine the smallest and largest people that can safely and efficiently operate each current USAF aircraft. 

In the past, aircraft were measured during the procurement process, to ensure they met the specifications set by the USAF, but not to determine the absolute limits of body size accommodation. Body size limit data for each aircraft will help policy makers determine if a change to AFI 48-123 is in the best interest of the USAF by indicating:

     1. If pilots of extreme size are safely accommodated in specific cockpits. 
     2. If there are adequate career paths available for pilots of extreme body size within the current and future USAF aircraft inventory, and 
     3. If there are cost effective modifications that could increase accommodation levels.

This research was carried out using live subject trials N= ~25 in each aircraft, and then used multiple regression to provide the best estimate for a particular accommodation parameter. We examined seven aspects of anthropometric accommodation in each aircraft. 

     1. Overhead clearance.
     2. Rudder pedal operation.
     3. Internal and external visual field. 
     4. Static ejection clearances of the knee, leg, and torso with cockpit structures. 
     5. Operational leg clearances with the main instrument panel. 
     6. Operational leg clearance with the control stick motion envelope (the pilot's ability to move the stick through its full range of travel).
     7. Hand reach to controls." 

1.0 INTRODUCTION

1.1 Background

" . . . With the procurement of the Joint Primary Aircraft Training System (JPATS or T-6)[*] and its eventual introduction into the USAF and USN  inventories, it will be possible to train pilots whose body sizes are considerably smaller than ever before. While the original design philosophy for JPATS was to accommodate all potential USAF pilots what meet AFI 48-123 requirements, during source selection this philosophy was modified to require accommodation of 95% of both the male and female military population, including whose who do not meet the restrictions in AFI 48-123. 

[* For a description of the JPATS T-6 Texan II click on JPATS.]

It is possible for pilots as small as 58 inches in Stature [Go to Instruction-48-123 for the prescribed Height/Weight Table] and 31 inches in Sitting Height to operate the T-6. However, after the T-6, student pilots must continue training in the T-1 (Tanker/Transport trainer) or the T-38A (Fighter/Bomber trainer). The T-1 and the T-38 were designed to accommodate a specific percentage (98% and 90%, respectively) of a population with a Stature range of 64 to 76 inches, and a Sitting Height range of 34 to 39 inches. (Recently, AETC extended the large size limit to 77 inches and 40 inches, respectively.)

This [accommodation range] is . . . true for the vast majority of USAF inventory aircraft, especially those designed in the 1950s and 1960s. Nearly all of these aircraft were designed to accommodate the body sizes of an all-male pilot corps. Data gathered on fleet aircraft show the smallest JPATS-eligible pilots (especially those with less than a five foot stature) will not be able to fly them safely. 

While the T-6 primarily increases accommodation for smaller pilots, it also accommodates somewhat larger pilots. Maximum Leg Lengths specified in the T-6 requirements documents were several inches larger than the lengths for which inventory aircraft were designed. These large, longer-legged pilots may suffer ejection injuries if they attempt to eject from follow-on aircraft with inadequate clearance space." 

1.2 Cockpit Accommodation

2.0 METHODS

"The first step in assessing accommodation in an aircraft was to determine what the pilot must be able to do to fly the aircraft safely. We call these baseline abilities Anthropometric Operational Requirements. These requirements were established in a six-step process. First, we reviewed T.O.-1 [Technical Order -1, "Dash Ones."] flight manuals for the aircraft  and examined all emergency procedures. Next, we interviewed selected instructor and safety pilots to determine a rough set of requirements. At this point, we asked pilots to fly both simulator sorties (to observe emergency procedures) and actual study flights (to determine minimum visual requirements) when possible. Using the results of these initial steps, we created a questionnaire and distributed it to as many experienced pilot as possible. In the case of training aircraft, we attempted to query 40 pilots at the instructor Pilot Training School at Randolph AFB, Texas. We used the results of this questionnaire to validate all earlier steps. The final step in the process was to submit the draft list of operational requirements to the appropriate Command headquarters for review and approval. For AETC, these requirements were signed by AETC/CC. For the other commands, signatures were obtained from AMC/CC, ACC/DO, and AFSOC/CV. Once these requirements were established, we completed the anthropometric portion of the research. . . ."

3.0 SMALL PILOT ACCOMMODATION

4.0 REACH TO RUDDERS

5.0 ARM REACH TO CONTROLS

"Reach to a particular control is a function of arm length, [sitting] shoulder height, and [sitting] eye height. Sitting Eye Height . . . plays a large role in seat adjustment, since the pilot must maintain at least minimally adequate vision. Moving the set up moves the pilot farther from most controls since the height of the shoulders relative to the control of interest directly influences the pilot's reach ability. 

Arm reach is also affected by the width of the shoulders, primarily because of the restraint system. On subjects with narrow shoulders, the torso harness may restrain forward movement of the shoulder. Wide-shouldered subjects, however, are better able to move their shoulders around the outside of the straps while reaching. 

To eliminate the need for a regression requiring three predictive variables, we substituted the variable Span for Thumb-Tip Reach and Biacromial Breadth, and created a two variable regression using Span and Sitting Shoulder Height. For some controls, particularly those overhead or on the aft portion of the side consoles, Shoulder Height is a significant variable in the regression equations. However, most of the controls . . . are forward of the shoulder, and the height of the shoulder was not significant in the resulting equation. Therefore, most of the time, only arm span is necessary to predict reach capability. 

6.0 STICK INTERFERENCE WITH THE THIGH

7.0 LARGE PILOT ACCOMMODATION

8.0 LEG CLEARANCE

9.0 FINAL ACCOMMODATION PERCENTAGES

10.0 SUMMARY OF RESULTS

11.0 USE OF THE DATA

"Software has been written and distributed which accepts input of an individual's anthropometric dimensions and gives [an] output of all aircraft in which that individual is accommodated. In the event that this document must be used for the same purpose, the procedure is as follows: First, small candidates must be measured for Sitting Eye Height, Shoulder Height Sitting (Acromion), Buttock-Knee Length, Knee Height Sitting, and Arm Span. First, compare the Sitting Eye Height measurements with the data in Table 3.2. If the candidate's Sitting Eye Height is less than 29.6 inches, this individual will not have adequate external vision in the T-38 or T-1. There would be no follow-on Trainer for this individual to fly. However, given the variability in anthropometric measurements, and the variability due to posture in the cockpit accommodation measurements, those who are close to 29.6 inches for Sitting Eye Height may be classified as marginal and given a "fit-check" in those aircraft. If the Sitting Eye height is greater than 29.6 inches, then it is important to calculate the amount greater and apply the adjustment listed in column three of Table 3.2. If for example, the candidate has a Sitting Eye Height of 30 inches, that value is 2.5 inches greater than the minimum requirement for the T-37. Since that seat adjusts in 0.625-inch notches, the candidate could lower the seat 4 notches and still see the minimum vision requirement. This will place the candidate much closer to rudders and hand controls. However, the candidate is only 0.4 inches larger than the minimum requirement in the T-1. The seat in this aircraft adjusts in 0.8-inch intervals. Therefore the candidate must remain in the full-up seat position for rudder and reach calculations. Those aircraft listed as 1/1 in Table 3.2 are continuously adjustable, so any amount of excess Sitting Eye Height can be subtracted directly from the seat position. At that point, classify the candidates as pass/fail (and possibly marginal) for each aircraft in Table 3.2. Next, using the seat position data, classify the candidate in each aircraft for reach to rudders using Table 4.2. The minimum Comboleg required for reaching full rudders from the full-up seat position is 40.5 inches. However, (using our candidate with a 30-inch Sitting Eye Height as an example) this person could sit 4 notches down, the minimum Comboleg from this position would be 39.5 inches. The last step is to again apply the seat position information, this time to Table 5.3 arm reach to controls. We will assume our candidate pilot has an arm Span of 63 inches and a Shoulder Height [Sitting] of 22 inches. The most restrictive reach requirement in [the] T-37 is full-forward stick with locked harness inertial reels. The equation for calculating miss distance to this control is miss distance = (.38603 X Shoulder Height Sitting (22 inches)) - (.70890 X Arm Span (63 inches)) + 34.4 inches. This equals -1.77 inches. A negative miss distance means the candidate went beyond the control by 1.77 inches and is a pass.* In addition, since the seat could be lowered 4 notches, the candidate would be 0.28 X 4 = 1.12 inches closer to the control. The final excess reach capability would be -2.89 inches. Once again it must be pointed out that there is variability (called statistical error) in this process and the numbers are best estimates. Those close to the minimum limits could be characterized as marginal and given live fit-tests.

Large pilots must be measured for Sitting Height and Buttock-Knee Length . . .  . Seat effect is irrelevant because the seat will travel up the rails during ejection, and we assume that if a candidate has overhead clearance problems the seat will have been adjusted full-down. Table 7.2 and Table 8.1 can be used directly. The same variability caveat applies to large candidates. Those very close to these limits could be classified as marginal and given a fit-check." 

* The convention would be to consider a "plus" value as one greater than that necessary to reach a given control. Multiplying the result by (-1) would satisfy this convention.

REFERENCES

APPENDIX A. Sorted Reach to Controls by Aircraft

APPENDIX B. Anthropometric Measurement Descriptions

APPENDIX C. Aircraft Functional Anthropometric Requirements

     Body Size/Reach Requirements for the A/OA-10, B-1, B-2, B-52,  F-117A, F-15, F-16, and HH-60G.
          Consisting of: Measurement Assumptions, Vision Requirement, Body Clearances/Size Requirements,
          Minimum Reach Requirements with Un-Locked Reels, and Minimum Requirements with Locked-Inertia
          Reels.

     Operational Requirements for the C-130, C-141, C-17, C-21, C-5, H-1, H-53J, KC-10, KC-135, and T-38.
          Consisting of: Vision Requirements, Minimum Reach Requirements with UN-Locked Reels and Minimum
          Requirements with Locked Inertial Reels

     Cockpit Accommodation Operational Requirements for T-1 and T-37.
          Consisting of: Vision Requirements, Body Clearances Requirements, Reach to controls with Locked Reels
          Requirement, and Rudder Requirements.

APPENDIX D. Staff Summary Sheets on Anthropometric Operational Requirements

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