What happened
While cruising at 6,500 feet, the pilot of the aircraft experienced significant engine vibrations and observed oil leaking from the engine cowling. As the intensity of both the vibration and the oil flow increased, the pilot shut down the engine and executed a forced landing into a field. During the aircraft's ground roll, it struck a berm approximately 2 feet in height.
The investigation
Post-accident examination of the engine identified that the number 2 connecting rod had failed between the crankshaft yoke and the wrist pin hole. A metallurgical analysis of the fracture surface revealed fatigue and evidence of gauling near the connecting rod bolt holes. Additionally, gauling was identified on the number 6 connecting rod bolt holes.
Findings
According to the engine manufacturer, the observed gauling can be caused by high loading conditions, such as those occurring during excessive manifold pressure operation or engine overspeed.