(1) Restraint systems should be designed to encourage frequent and proper use by occupants. Restraints which are complex, uncomfortable, or unduly restrictive to normal operational functions of the occupant are unlikely to be successful.
(2) Restraints should fit the size range of occupants that are likely to use the system. Misfit restraint systems can cause injury; for example, a diagonal belt which bears against the side of the head can promote neck injury if vertical impact takes place; a diagonal belt which passes below the center of mass of the upper torso-head-neck complex may allow the torso to rotate out of the restraint and increase the potential of either impact with the aircraft interior or injury from spinal column torque, etc.
withstand the loads (i.e., pelvis or shoulders), and should not move from those (3) Restraints should apply loads to the body areas most able to areas during the impact.
(4) Seats and restraints should distribute their load over a maximum body contact area to reduce concentrated load on the body.
(5) Seat and restraint systems should provide as much uniform load distribution to the body as possible to limit relative displacement of the body segments.
(6) Elasticity of elements in the restraint and seat allows body motion and can increase impact severity. For example, long lengths of restraint webbing stretch more than short webbing lengths and allow more occupant motion.
criteria and test procedures which have been accepted by user groups and have Accepted Injury Criteria. The following documents contain injury served as guidance for establishing similar criteria for civil aircraft crash injury protection systems:
(1) Federal Motor Vehicle Safety Standard No. 201, Occupant protection in interior impact (49 CFR 571.201), contains criteria for head impact with instrument panels and seat backs.
injury in rear-end collisions, and may be applicable to rear facing seat, head rest design in aircraft.
(3) Federal Motor Venicie Safety Standard No. 203, Impact protection for the driver from the steering control system (49 CFR 571.203), contains criteria to minimize chest, neck, and facial injuries resulting from impact with the steering control.
(4) Federal Motor Vehicle Safety Standard No. 208, Occupant crash protection (49 CFR 571.208), contains criteria for the head, thorax, and upper legs to minimize injury in an automobile crash.
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(5) Military Specification 58095(AV), General Specification for Crashworthy, Non-Ejection, Aircrew Seat System (MIL-S-58095(AV)), contains specifications for limiting spinal injury created by whole body vertical acceleration.
f. Suggested Numerical Values for Aircraft Use. The following subparagraphs summarize the impact injury data that are suggested herein for use in assessing the performance of impact injury protection systems in civil aircratt, and these data are not to be considered as regulatory criteria. It is not intended that all of the suggested performance criteria should be used in every case to assess each impact injury protection system. when regulatory requirements are established, specific performance criteria will be defined within the rule. In such cases, the regulatory criteria take precedenc- over anything presented in this advisory circular. In the absence of a definitive regulatory requirement though, a manufacturer should select appropriate performance criteria, develop appropriate test procedures for the particular application, and demonstrate that the selected performance criteria have been met.
(1) Whole body impact tolerance -
(1) - Gx (2-point restraint) Figure 1
(ii) + Gz (2-point restraint) Figure 2
(iii) - Gy (2-point restraint) Figure 3
(iv) - G (3-point restraint) Figure 4
(2) Head injury - HIC ‹ 1000 (t2-t1 < 0.05 seconds)
(3) Chest injury - Diagonal shoulder belt load - 7.8 kN (1750 1bs.)
(4) Abdominal injury - No quantitative data suggested.
(5) Leg injury -
(i) In line with femur - 10 kN (2250 1bs.)
(ii) Patella (concentrated load) - 2.5 kN (560 lbs.)
(iii) Transverse (lower leg) - 4.45 kN (1000 1bs.)
(6) Spinal injury - Pelvic compression load - 6.7 kN (1500 lbs.)
A. Pontecosio oseph A. Pontecorvo Deputy Director of Airworthiness Par 6 13