1Civil Aerospace Medical Institute, Federal Aviation Administration, Oklahoma City, OK, USA
2Aviation Safety, Federal Aviation Administration, Washington, DC, USA
The Federal Aviation Administration (FAA) has adopted safety requirements intended to protect aircraft occupants during survivable crash scenarios. These requirements include design specifications, static strength tests and dynamic impact tests of seats and restraint systems using instrumented Anthropomorphic Test Devices (ATD). Two orientations of impact test are cited: a combined longitudinal/vertical test with the impact vector 60° from horizontal, and a longitudinal test with the impact vector yawed 10° from the centerline of the aircraft. Injury potential is assessed during the dynamic tests by comparing test results to a set of injury criteria. The static and dynamic test requirements vary by aircraft type due to the differences in energy transmitted to the seats. However, the injury criteria evaluated during these tests are very similar for all aircraft types. The criteria cited in the regulations are: the Head Injury Criteria (HIC), lumbar spine compressive load, shoulder strap load, femur compressive load (for passengers of transport aircraft only), a requirement that the seat belt not bear on the abdomen, and that the shoulder belts (if used) bear on the shoulder.
Side facing seats have unique injury risks. Therefore, tests using an ATD that can measure those risks (the ES-2re) are conducted to ensure that side facing seats provide the same level of safety as forward or aft-facing ones. The injury criteria originally developed to evaluate side impacts in autos have been cited in the aviation requirements, and include: HIC, rib lateral deflection, abdomen force, and pubic symphysis force. Because aircraft side-facing seats do not always provide full support for the occupant, additional criteria were developed to limit the risk of injuries caused by excessive excursion of the head, torso and legs. These criteria place limits on upper neck loads, femur twist angle, and torso flail, and prohibit significant contact between occupants of multi-place seats.
As new seat configurations and restraint technologies are introduced, additional criteria may be needed to ensure that these new systems provide the same level of safety as conventional seats and restraints. Advancements in biomechanics and injury mitigation technology have the potential to increase the level of safety for all aircraft occupants.