Primary finding
Probable cause
The pilot’s failure to maintain adequate main rotor RPM during an autorotation which resulted in a hard landing and subsequent rotor blade strike of the tail boom.
Investigator assessment
Analysis narrative
The flight instructor reported that he was demonstrating a 180° autorotation for his passenger into an open field off airport grounds. Nearing the end of the maneuver, prior to touchdown, he failed to recover engine power in a timely manner which resulted in the rapid decay of the rotor rpm at low altitude; this resulted in a hard landing that subsequently caused the main rotor blades to make contact with the tail boom and severed the tail rotor driveshaft. The helicopter sustained substantial damage to the fuselage and the main rotor blades. The pilot reported that there were no pre accident mechanical malfunctions with the helicopter that would have precluded normal operation.