NTSB Identification: MIA06IA110.
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Incident occurred Tuesday, May 23, 2006 in St. Augustine, FL
Probable Cause Approval Date: 02/28/2008
Aircraft: Cessna 172S, registration: N1130T
Injuries: 1 Uninjured.

NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.

The airplane experienced a loss of engine power due to failure of the crankshaft and separation of the propeller and propeller flange during the initial climb shortly after takeoff. The pilot reversed course and landed on a taxiway at the departure airport without further incident. At the time of the event, the airplane and engine had accumulated a total time of 399.3 hours. Metallurgical examination determined that the crankshaft separation was the result of a lubrication failure at the #2 main bearing. The lubrication failure then allowed excessive friction to overheat the bearing journal on the crankshaft producing ladder cracks in the surface and at the oil transfer hole. These cracks in turn initiated torsional fatigue cracks that ultimately lead to the separation of the crankshaft. The root cause of the lubrication failure was likely the result of intermittent oil flow to the bearing or of 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.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

The loss of engine power due to separation of the crankshaft as a result of lack of adequate oil lubrication to the #2 main bearing. The lack of oil lubrication was most likely the result of improper assembly (fitting) of the bearing shells to the crankshaft.

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