Accident Summary
A commercial pilot was operating a non-scheduled domestic cargo flight carrying mail when the engine lost all power at an altitude of about 1,000 feet above ground level. The pilot executed a forced landing onto rough, tundra-covered terrain. During the landing, the airplane nosed over.
Engine History and Examination
The engine had been overhauled 1,090.9 flight hours prior to the accident. As part of the overhaul, the engine case was sent to a vendor for welding and reboring to match original specifications.
A postaccident examination of the engine revealed significant damage. The number 1 main bearing was deformed in its bearing saddle. Portions of the number 2 main bearing were flattened, fractured, and fragmented, with fragments found in the engine case. The number 2 bearing saddle was extensively distorted and gouged. The crankshaft was fractured at the radius of the number 2 main bearing and the number 3 crankshaft cheek, adjacent to the main bearing surface. The fracture surface exhibited discoloration consistent with high heat and beach marks characteristic of fatigue.
Under the bearing insert, the number 2 bearing saddle area had several cracks and exfoliation of the case material along the edges of the oil supply channel. No evidence of engine case fretting was observed.
Metallurgical Analysis
The manufacturer's metallurgical personnel examined the engine case. Their report stated that the case showed no signs of lubrication distress on the journals. Regarding the weld repair at the number 2 main bearing support, the manufacturer's metallurgist indicated that a determination could not be made with a high degree of certainty, although multiple work order stamps on the crankcase suggested it had been reworked.