Accident Sequence
According to the pilot's written statement, he climbed to 6,000 feet mean sea level to practice aerobatic maneuvers and entered a left upright spin. After two turns, he initiated a forward movement of the control stick to recover but discovered that the stick was jammed in the full aft position. Upon inspection, he found that the rear seat back frame had fallen forward, looped over the stick, and was holding it in place. After several unsuccessful attempts to reach the seat back and free the stick, the pilot abandoned the airplane and parachuted to the ground. The pilot reported that the aircraft continued its spin until ground impact.
Cause of Control Loss
The pilot identified the fallen rear seat back frame as the cause of the control stick jam. The seat back frame had become dislodged from its normal upright position and entangled with the control stick, preventing any forward movement necessary for spin recovery.
Safety Cable Issue
The pilot noted that a safety cable is intended to hold the rear seat back frame upright during maneuvers to prevent interference with the rear control stick. During the preflight inspection, the pilot observed that the safety cable was present. However, after the accident, a flight instructor informed the pilot that the cable had reportedly been disconnected from its attach point by maintenance personnel to facilitate access to the aircraft battery and the area behind the rear seat where the emergency locator transmitter was located.