Mechanism of vertebral fracture in the F/FB-111 ejection experience.

A review of the accident investigation reports of all non-fatal F/FB-111 ejections which occurred from 19 October 1967 to 26 March 1980 was conducted. The available spinal radiographs of the ejectees were also reviewed. The overall rate of vertebral compression fractures among the survived ejectees in a properly functioning module is 29.5% (23 of 78). The general mechanism of vertebral injury is a combined mechanism involving both axial compression and flexion. There is no evidence to indicate a hyperextension injury mechanism during retraction, nor is there evidence to support the presumed efficacy of the crossed-arms bracing procedure recommended for landing impact in modifying the vertebral injury rate. It appears that a significant reduction in the rate of vertebral fractures among F/FB-111 ejectees will require decreasing the acceleration stresses imposed on the crewmembers during landing impact.