What happened
The incident occurred while the aircraft was engaged in agricultural operations, specifically dispensing Systox herbicide over an apple orchard. During this phase of flight, the pilot sensed that the engine was binding, which was immediately followed by a loss of power. In response to the mechanical failure, the pilot elected to dump the remaining herbicide load and initiated a power-off autorotation. The aircraft was successfully landed in a nearby grape vineyard without further incident.
The investigation
A physical examination of the helicopter's engine revealed significant internal damage. Investigation determined that the connecting rod for cylinder #5 had overheated at the bearing journal. This thermal stress caused the bolt to break, resulting in the cap separating at the parting surface. This mechanical failure was identified as the direct cause of the engine binding and subsequent power loss.
Findings
The primary factor contributing to the event was the structural failure of the cylinder #5 connecting rod due to overheating. The pilot's decision to dump the chemical load and execute an autorotation allowed for a controlled landing despite the complete loss of engine power.