What happened
A pilot and three passengers were operating an air taxi flight over remote terrain when, while cruising at approximately 2,200 feet, the engine oil pressure began to decrease and the engine oil temperature began to rise. In response to these indications, the pilot attempted to divert to the nearest airport. During the diversion, the engine stopped running.
The pilot identified an emergency landing area on a sand bar located along a river, which contained several willow trees. During the course of the landing, the Cessna (type not specified in source) sustained damage to its wings and fuselage. There were no fatalities among the four occupants.
The investigation
An examination of the engine, which had accumulated 1,491 hours since its last overhaul, revealed that the crankshaft was broken. Specifically, the fracture occurred along the aft, lower edge of the number two cheek journal at the forward radius of the number two main bearing journal. The fracture line was described as straight and flat, extending through the full dimension of the number two cheek journal and oriented perpendicular to the longitudinal axis of the crankshaft.
Further inspection showed that the number two main bearing was broken and flattened, and the number two main bearing saddle had also been flattened and distorted. Additionally, the mating surfaces of the left and right engine case halves exhibited galling and fretting at the number two main journal bolt holes.