The brace position for passenger aircraft : a biomechanical evaluation
Hypothesis A modified brace position would help to prevent injury to some aircraft passengers in the event of an impact accident. Aim of Experiments To evaluate a modified crash brace position. Materials and Methods 1. Impact Testing Impact testing was performed at the RAF Institute of Aviation Medicine, Farnborough. Aircraft seats, mounted on a sled, were propelled down a track at an acceleration of 16G. A 50% Hybrid III dummy was used as the experimental model. Four dummy positions were investigated: upper torso either braced forwards or sitting upright and lower legs placed either forwards or rearwards. The impact pulses used were based upon guidelines defined in Aerospace Standard AS8049 which relates to the dynamic testing of aircraft seats. Transducers located in the head, lumbar spine and lower limbs of the dummy recorded the forces to which each body segment was exposed during the impact. These forces were compared for each brace position. 2. Computer Simulation A mathematical model was developed to simulate occupants kinematics during an impact aircraft accident. This was based upon MADYMO -a crash victim simulation computer programme for biomechanical research and optimization of designs for impact injury prevention. Results Impact testing revealed that the risk of a head injury as defined by the Head Injury Criterion was greater in the upright position than in the braced forwards position (p < 0.00 1). The risk of injury to the lower limbs was dependant in part to their flailing behaviour. Flailing did not occur when the dummy was placed in a braced legs back position. Computer simulation revealed that lower limb injury may result from the feet becoming entrapped under the luggage retaining spar of the seat ahead. Conclusion A modified brace position would involve passengers sitting with their upper torso inclined forwards so that their head rested against the structure in front if possible. Legs would be positioned with the feet resting on the floor in a position slightly behind the knee. This position differs from those previously recommended in that the feet are positioned behind the knee. This study suggests that such a position would reduce the potential for head and lower limb injury in some passengers given that only a single seat type and single size of occupant have been evaluated. Standardisation to such a position would improve passenger understanding and uptake. Such a recommendation should not obscure the fact that an occupant seated in a forward facing aircraft seat, restrained only by a lap belt is exposed to considerable forces during an impact accident. Such forces are capable of producing, injuries in the femur, pelvis and lumbar spine.