What happened
While conducting a non-scheduled domestic cargo flight carrying mail, a Cessna (type not specified) was in cruise flight at approximately 1,000 feet above ground level when the engine lost all power. The pilot executed a forced landing into rough, tundra-covered terrain. During the course of the landing, the aircraft nosed over.
The investigation
The engine had been overhauled 1,090.9 hours prior to the accident. During that overhaul process, the engine case had been sent to a vendor for welding and reboring to meet original specifications.
A post-accident examination of the engine revealed significant internal damage. The number 1 main bearing was deformed within its bearing saddle, and portions of the number 2 main bearing were found flattened, fractured, and fragmented inside the engine case. Additionally, the number 2 bearing saddle showed extensive distortion and gouging.
The engine crankshaft suffered fractures at the radius of the number 2 main bearing and the number 3 crankshaft cheek near the main bearing surface. The fracture surfaces exhibited discoloration indicative of high heat and beach marks consistent with fatigue. Furthermore, the area of the number 2 engine bearing saddle beneath the bearing insert showed several areas of cracking and exfoliation of the case material along the edges of the oil supply channel.
While no evidence of engine case fretting was observed, the manufacturer's metallurgical examination noted that while there were no signs of lubrication distress on the journals, several work order stamps indicated the crankcase had been reworked. The metallurgist could not determine with high certainty if a weld repair had occurred at the number 2 main bearing support.