Overview
A helicopter equipped with a newly installed clutch assembly was damaged during an autorotation practice flight conducted shortly after sunset. The pilot, who intended to verify the clutch's performance, completed one successful autorotation before encountering issues during a subsequent maneuver.
Flight Details
The pilot reported that visibility was adequate during the evening flight, with runway lights clearly visible despite twilight conditions. The first autorotation proceeded normally. For the second, the pilot aimed to check main rotor rpm but noted that the rotor speed was lower than expected. Despite the low rpm, the low rotor warning horn and light did not activate.
During the descent, the pilot attempted to increase rotor rpm by adjusting airspeed up to the flare point. Witnesses observed the helicopter commence a flare at approximately 50 feet above the runway, followed by a hard landing. The helicopter then became airborne again, spun, and landed hard a second time, rolling onto its left side.
Post-Accident Examination
An examination of the helicopter revealed no evidence of mechanical failure. The accident occurred at 1802, with sunset at 1733 and the end of civil twilight at 1759.
Conclusion
The accident occurred during a routine operational check following a maintenance action, with the reported low rotor rpm and lack of warning indication being the primary operational anomalies.