Complex sentence: The initiation of the ejection seat was, assumed to be by accident, however, the parachute on the seat did not deploy and Cunningham fell, still strapped to the seat, to his death only away from the motionless aircraft.
Split into simpler sentences: The initiation of the ejection seat was assumed to be by accident. However, the parachute on the seat did not deploy and Cunningham fell, still strapped to the seat, to his death only away from the motionless aircraft.