Event Description
During the initial climb shortly after takeoff, the airplane experienced a loss of engine power. The pilot reversed course and landed on a taxiway at the departure airport without further incident.
Investigation Findings
Metallurgical examination determined that the engine power loss resulted from a failure of the crankshaft, which also led to the separation of the propeller and propeller flange. The crankshaft separation was caused by a lubrication failure at the #2 main bearing. The lubrication failure allowed excessive friction to overheat the bearing journal on the crankshaft. This overheating produced ladder cracks in the surface and at the oil transfer hole. These cracks initiated torsional fatigue cracks that ultimately led to the separation of the crankshaft.
The root cause of the lubrication failure was likely either intermittent oil flow to the bearing or improper assembly (fitting) of the bearing shells to the crankshaft. Considering that the other bearings did not show distress and the short time since engine assembly, it is more likely that an assembly issue was the cause. No preexisting metallurgical or mechanical discrepancies were found with the crankshaft.
At the time of the event, the airplane and engine had accumulated a total time of 399.3 hours.
Probable Cause
The probable cause of the engine power loss was improper assembly of the bearing shells, leading to a lubrication failure at the #2 main bearing, which resulted in crankshaft separation.