Incident Summary
While conducting a routine power line patrol flight, the pilot heard a loud noise emanating from the engine compartment. Immediately thereafter, the helicopter experienced a yaw to the left, and the pilot observed split engine and rotor RPM indications. Recognizing a loss of engine power, the pilot executed an autorotation. The descent was carried out over a partially cleared area, but during the landing, the helicopter struck trees and then impacted the terrain.
Engine Failure Details
Post-accident inspection of the engine revealed that the number four connecting rod belt had failed. This failure allowed the connecting rod to separate from the crankshaft. The detached connecting rod then jammed itself against the crankshaft, which resulted in a complete stoppage of the engine. No other mechanical anomalies were reported.
The helicopter sustained damage from the impact with trees and terrain. The pilot was the sole occupant, and no injuries were mentioned in the source.