Accident Overview
During a routine pipeline patrol flight, the pilot experienced a sudden loss of engine power. In response, the pilot executed an autorotation landing in an open field. The event occurred without any prior indication of engine trouble.
Investigation Findings
Post-accident examination of the engine revealed that the number one cylinder connecting rod cap had fractured. A metallurgical analysis of the fracture surface identified a fatigue crack that originated from a galling mark on the bearing surface of the connecting rod. The engine had been operated for 39 hours since its last overhaul.
Metallurgical Analysis
The fatigue crack exhibited characteristics typical of progressive failure. The initiation point was a galling mark, which is a form of adhesive wear caused by metal-to-metal contact under load. Over time, cyclic stresses propagated the crack until the rod cap could no longer withstand the loads, resulting in a complete fracture and subsequent loss of engine power.
Operational Context
The aircraft was engaged in low-altitude pipeline patrol operations. The autorotation landing was conducted in an open field, which allowed the pilot to set the aircraft down without further incident. No other anomalies were noted in the engine's operating history or maintenance records prior to the event.