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Actual automobile crash scenarios include “wheels-first” landings after the vehicle leaves the road surface and becomes momentarily airborne. These events generate a vertical acceleration vector in a headward direction (+Gz) along the occupant's spinal axis. In this scenario, the vehicle occupant could be in contact with the seat bottom or seat back cushions, or displaced several inches off both the bottom and/or back cushions depending on the effectiveness of the restraint configuration and the dynamics of the vehicle's motion. Military ejection seat researchers have shown that occupant response to +Gz acceleration loading is amplified as a function of the spring-mass damping characteristics of the total system (i.e., the occupant and seat/restraint/cushion subsystems). This amplification phenomenon, commonly known as “dynamic overshoot”, has the propensity to vary widely depending on the built-in controls within a given seat bottom design.

This paper discusses the ongoing real-world effects on the wearers of restraint systems which are subject to a retractor's failure to lock in a timely manner. Investigation of the ELR performance using both detailed physical examination and inductive methods enables accurate assessment of successful ELR locking at the first opportunity in the crash sequence. Available methods to determine the reliability of the ELR's crash performance are considered and analyzed for assessment of reliability to enable adequate seat belt wearer protection. Corrective measures are analyzed to probe the feasibility of federal safety regulation amendments to mandate a reliability analysis on the propensity for the ELR's failure to lock in a timely manner.