During which phase of an ejection is dynamic overshoot most likely to cause femur fractures?

Dynamic overshoot occurs during the ejection sequence primarily due to rapid deceleration forces acting on the pilot's body. In the aircraft separation phase, after ejection from the aircraft, the pilot is subjected to high-speed wind impacts and abrupt deceleration as the ejection seat discharges and separates from the aircraft. This phase is critical because the pilot’s body continues forward momentum while the ejection seat and parachute are beginning to deploy, creating significant stress on the skeletal structure, particularly the femurs.

When the dynamic forces are in play during this phase, it can lead to the femur undergoing torsional or bending forces that exceed its strength, resulting in fractures. The rapid transition from high-speed flight to a slowed state without adequate support or stabilization can lead to these high-impact injuries. In contrast, other phases like the in-seat flight phase or parachute descent phase do not typically exert the same level of dynamic forces on the femurs, as the body is more stabilized or subjected to different types of forces. Thus, the aircraft separation phase is the most critical for femur fracture risk due to dynamic overshoot.