Vertical impact evaluation of the F/FB-111 crew restraint configuration, headrest position, and upper extremity bracing technique.

An experiment to assess the influence of changes in restraint harness configuration, fore-aft headrest position, and upper extremity bracing technique on human response to impact was conducted using the AFAMRL Vertical Deceleration Tower. A total of 201 tests was performed with volunteer subjects in 11 test conditions to evaluate 3 restraint harnesses, 3 arm bracing conditions, and 4 seat adjustment configurations. The test fixture, restraint harness, and subject were instrumented to obtain pertinent objective data during each experiment. Measured parameters included acceleration of the impact carriage and test seat, velocity of the carriage, loads reacted at the seat, loads measured at the restraint harness attachment points, triaxial translational accelerations at the head and chest of the subject, and body segment displacements. The mean peak carriage acceleration for the 161 experimental level tests was 10.5 G (S.D. = 0.18) and the mean carriage velocity change was 7.89 m/s (S.D. = 0.05). Resultant head and chest accelerations were increased in a proposed, modified F/FB-111 restraint system compared to the operational F/FB-111 restraint system. These findings contributed to the decision not to implement the proposed modification. Also, the arms crossed bracing position for F/FB-111 ejectees preparing for landing impact of the crew module was associated with higher seat loads than the arms extended position. With the arms extended and braced on the anterior thighs or knees, loads are transmitted through the extremities to the footrest thereby reducing loading of the vertebral column. Operational use of the arms extended position prior to anticipated vertical impact accelerations may be helpful in reducing the vertebral fracture rate associated with these mechanical force environments.