Accident Overview
A helicopter accident occurred during a planned power-recovery 180-degree autorotation training maneuver to a plowed field. The flight instructor reported that the student pilot initiated the maneuver. At an altitude of approximately 20 to 50 feet above ground level, the instructor observed that the engine rpm needle was not aligning with the rotor rpm needle. The instructor immediately attempted to roll maximum throttle on but found that the throttle would not move. The student informed the instructor that the throttle was stuck. However, the instructor noted that the throttle seemed stuck because it was all the way open. The instructor then took control of the helicopter.
Sequence of Events
Shortly after the instructor took control, the helicopter contacted the ground. The right skid dug into the terrain, causing the helicopter to roll over and come to rest on its right side. The instructor stated that when he took the controls, the engine was not running and the throttle was in the wide-open position.
Investigation Findings
Post-accident examination revealed no mechanical anomalies with the engine or the airframe. Despite thorough investigation, the reason for the loss of engine power could not be determined.