What happened
The aircraft was involved in an incident while conducting a practice autorotation training exercise. The certified flight instructor (CFI), who was on board, observed that the student pilot was approaching an overshoot condition during the maneuver. At an altitude of approximately 100 feet above ground level, the CFI instructed the student to initiate a power recovery.
Shortly after the command was given, the aircraft began to shudder and entered a high sink rate. When the CFI assumed control of the aircraft, he noted that the rotor revolutions per minute (RPM) had fallen below the proper operational range and were continuing to decay. Additionally, the engine RPM was observed to be near zero.
The CFI reported attempting to recover by fully lowering the collective pitch ('bottoming' it) and opening the throttle; however, the engine did not respond as expected. Despite these efforts to regain control and altitude, the aircraft impacted the ground in a tail-low attitude with a left yaw. Following the initial impact, the aircraft slid approximately 20 feet before rolling over.
The investigation
Following the accident, Federal Aviation Administration (FAA) personnel inspected the engine. They found that the engine started and ran normally after the rollover. Operational checks confirmed proper magneto function and a smooth idle at 1300–1350 RPM. When the RPM was manually reduced to 500–600 RPM, the low-side cushion returned the engine to normal idle upon throttle release. No evidence of an engine malfunction was found during this post-accident examination.