Overview
During a ferry flight to conduct an aerial application operation, the pilot reported that the engine began to overspeed. In response, the pilot entered an autorotation to reduce engine rpm. The maneuver required clearance of power lines, during which rotor rpm decayed. The aircraft subsequently dropped from an estimated altitude of 50 to 75 feet above ground level (AGL).
Sequence of Events
The pilot was ferrying the helicopter to the operational site when the engine overspeed occurred. To counter the overspeed, the pilot initiated an autorotation. While in autorotation, the pilot had to avoid power lines. To clear them, the pilot utilized the rotor rpm, which resulted in a decay of rotor speed. The loss of rotor rpm caused the helicopter to descend rapidly from approximately 50 to 75 feet AGL, resulting in a hard landing.
Post-Accident Investigation
A post-accident investigation revealed a malfunctioning main transmission centrifugal clutch. The powerplant was tested following the accident, and no malfunction was identified. An annual inspection had been performed 6 days and 4 hours of flight time prior to the accident.