One of the key issues that must be addressed in any aircraft accident is the question of crash survivability. The crashworthiness design of an aircraft is largely based on experience, history, and sound engineering assumptions. Often times, it takes an actual accident to verify that the design was sufficient to prevent real world injuries. When injuries do occur, the Aircraft Accident Investigator has to determine what caused the injuries, did the injuries have to occur, and could something have been done to eliminate or reduce their severity. Fortunately, DVI’s Aircraft Crashworthiness Experts are very good at systematically identifying the various factors which influence the potential survivability of the crash. DVI’s Crashworthiness Experts consider a potentially survivable aircraft crash as one in which the deceleration forces transmitted to the occupants did not exceeded the human tolerances and in which the structure surrounding the occupants remained substantially intact. DVI’s Crashworthiness Experts evaluate five aircraft design features to determine survivability: 1) “Container” – in order to survive an impact of crash it is first necessary to provide a “living space” for the occupants during the dynamic portion of the crash. If this space is breached, the chance of survivability is drastically reduced. 2) “Restraint” – If the occupants have been provided an adequate “living space” then they must be restrained within that space to be protected from flailing about. The strengths of the restraints should be sufficient enough to prevent injuries from the highest anticipated loading that is considered survivable. Some of the issues which are of special interest to restraint systems are: varying strength requirements along the aircraft’s three axis, the influence of dynamic loading, uneven sharing of loads when multiple restraints are used, the propensity of the restraint system to injure the occupant, and the ease of restraint system release for existing the aircraft after the crash. 3) “Energy Absorption”- Since the occupants are not rigidly attached to the airframe, the design of the aircraft structure and the seats may cause the acceleration forces experienced by the occupants to be either amplified or attenuated. For example, a soft deep seat cushion can greatly amplify vertical Gs, whereas a deep seat cushion that deforms only at high speeds, absorbing energy as it gives, can mitigate vertical Gs. 4) “Environment”- Designers should make all attempts to delethalize the occupant container to prevent obstructions from causing injuries. 5) “Post Crash Conditions”- Unfortunately, the primary factors in the causation of fatalities during otherwise survivable crashes is the post crash fire and inability to quickly exit the damaged aircraft. Control of fire is one of the key issues in crash survival.
Depicted below are typical loading charts that illustrate the human tolerances for G forces in the horizontal and vertical directions.