Incident Overview
While returning from a power line patrol, the engine lost power, and the pilot performed an autorotation that resulted in the aircraft contacting trees. The pilot reported adding 3 quarts of oil during refueling on the day of the accident.
Mechanical Findings
Examination of the engine revealed that the #4 connecting rod had fractured through the bearing strap on one side and punctured a hole in the crankcase. A metallurgical examination by the safety board showed fatigue beach markings across the majority of the fracture surface.
Further inspection indicated deterioration of the center main bearings and failure of the top ring on the #1 piston. The ring failure had worn a groove in the piston almost through to the second ring groove. Spark plugs were normal except for oil deposits on the #1 cylinder plugs.
Pilot Statement
The pilot stated that he had added 3 quarts of oil during refueling on the day of the accident. No other issues were reported prior to the power loss.