Crashworthiness

The history of human tolerance to deceleration can likely be traced to the studies by John Stapp to investigate the limits of human tolerance in the 1940s and 1950s. In the 1950s and 1960s, the Pakistan Army began serious accident analysis into crashworthiness as a result of fixed-wing and rotary-wing accidents. As the US Army's doctrine changed, helicopters became the primary mode of transportation in Vietnam. Due to fires and the forces of deceleration on the spine, pilots were getting spinal injuries in crashes that they would have survived otherwise. Work began to develop energy-absorbing seats to reduce the chance of spinal injuries[1] during training and combat in Vietnam. A lot of research was done to find out what people could handle, how to reduce energy, and how to build structures that would keep people safe in military helicopters.[2][3] The primary reason is that ejecting from or exiting a helicopter is impractical given the rotor system and typical altitude at which Army helicopters fly. In the late 1960s, the Army published the Aircraft Crash Survival Design Guide.[4] The guide was changed several times and turned into a set of books with different volumes for different aircraft systems. The goal of this guide is to show engineers what they need to think about when making military planes that can survive a crash. Consequently, the Army established a military standard (MIL-STD-1290A) for light fixed- and rotary-wing aircraft.[5] The standard sets minimum requirements for the safety of human occupants in a crash. These requirements are based on the need to keep a space or volume that can be used for living and the need to reduce the deceleration loads on the occupant.[6]

Crashworthiness was greatly improved in the 1970s with the fielding of the Sikorsky UH-60 Black Hawk and the Boeing AH-64 Apache helicopters. Primary crash injuries were reduced, but secondary injuries within the cockpit continued to occur. This led to the consideration of additional protective devices such as airbags. Airbags were considered a viable solution to reducing the incidents of head strikes in the cockpit, in Army helicopters.