Research on occupant survivability of impact is over half a century old, and serious advances in knowledge about the subject were made through Colonel John Stapp in the 1950's. He successfully survived a 46.2g deceleration, as documented in this clip.
Colonel Stapp also tested accelerations up/downwards. backwards and sideways. From this fascinating article:
Stapp’s first project was analyzing plane crashes, or rather, why people were crashing in planes. Going into the project, the years prior and throughout the Second World War aircraft engineers and designers decided that humans could survive at a maximum of 18G 3. Airplane cockpits then were all designed to withstand 18G impacts because if the person was already dead, why invest in stronger materials and structural support. Just how this figure was achieved, why, from whom, etc. immediately came into question by Stapp and his group who had been carefully reviewing vast amounts of accident reports that had started to reveal some contradictory evidence against this number.
The article is from the Motorsport Safety Foundation, and indeed according to the Wikipedia article, Colonel Stapp was
..chairman of the annual Stapp Car Crash Conference. This event meets to study car crashes and determine ways to make cars safer. In addition, Stapp was honorary chairman of the Stapp Foundation, which is underwritten by General Motors and provides scholarships for automotive engineering students.
Advances in car crash survivability thus were started in military aviation, then further advanced and applied in the motor car industry. Civil aviation has been a laggard, partly explained by the very few accidents and the high proportion of fire on board after crashes: passengers who survived the crash then succombed in the fire.
Crash survivability is discussed in this 1980 Flight Magazine article as well, including the following table showing that cicil aviation specs were lagging behind military and flight medical recommendations:
Civil Regulation standards
Passenger aircraft manufactured before 2009 had to comply to the following safety standards for seats and safety belts:
- 14 CFR 25.561. Accelerations that the seats must withstand, demonstrated with tests using dummies:
- Upward, 3.0g
- Forward, 9.0g
- Sideward, 3.0g on the airframe, and 4.0g on the seats and their attachments.
- Downward, 6.0g
- Rearward, 1.5g
- 14 CFR 25.562. Requirements on testing with a 170 lbs test dummy and:
- nose down 30º, peak floor deceleration > 14g
- nose level, peak forward deceleration > 16g, yawed 10º to demonstrate the capability of seat restraint to successfully restrain the passenger when side forces apply.
- maximum levels of impact force for pelvis, head, legs.
- requirement that the seats must remain attached at the end of the tests.
- 14 CFR 121. Under A. History, the text describes what improvements to standards were made to seat and seat restraints structural requirements.
Amendment 25-64 upgraded the certification standards for occupant protection during emergency landing conditions in transport category airplanes from only a 9g static standard to an upgraded 9g static standard and a new 16g dynamic standard.
Not civil, but the best: Aircraft Crash Survival Design Guide, link to pdf of first of five volumes, pointed out by @Peter Kämpf
- The Cherry study, discussed here, made recommendations for implication of measures and for further study.
- The European Transport Safety Council study, further building on the Cherry report and making additional recommendation. The study states its limitations very clearly, yet distills methods for further improving survivability.
- Studies into use of airbags, such as mentioned here.