Accident Overview
A helicopter accident occurred during a zero ground speed practice autorotation. According to witness accounts, the maneuver was being performed as part of training when the rotorcraft developed a high rate of descent after the pilot attempted to correct for decreasing rotor RPM. The helicopter subsequently contacted the ground tail first, and the main rotor severed the tail boom, causing the aircraft to roll over.
Witness Statement
An experienced helicopter pilot who witnessed the accident reported that the autorotations were terminated abruptly with an extremely nose-high attitude. The witness noted that the termination technique appeared to contribute to the sequence of events leading to the ground contact.
Sequence of Events
The accident sequence began during a zero ground speed autorotation, a maneuver intended to simulate a power-off landing with minimal forward motion. During the descent, the pilot observed a decrease in rotor RPM and attempted to correct it. This corrective action was followed by a high sink rate, which the pilot was unable to arrest before the helicopter struck the ground. The impact occurred tail first, and the main rotor blades subsequently cut through the tail boom, causing the helicopter to roll onto its side.
Conclusion
The accident resulted from a loss of rotor RPM during autorotation and an abrupt termination that led to a nose-high attitude and tail-first ground contact. No further causal factors were identified in the source material.