NTSB Identification: ANC96LA140.
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Nonscheduled 14 CFR
Accident occurred Sunday, September 01, 1996 in SKWENTNA, AK
Probable Cause Approval Date: 03/31/1998
Aircraft: Piper PA-28-161, registration: N4366Y
Injuries: 1 Minor,2 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The pilot & 2 passengers departed on a local area sightseeing flight. While in cruise flight at about 4,000 ft, the engine developed a vibration, then lost power. Oil spray was deposited on the windshield. The pilot performed an emergency landing on a sand bar. After landing, he noticed that the entire propeller, propeller flange, & the outboard end of the engine crankshaft were missing from the engine. Examination of the engine revealed evidence of fatigue cracking, emanating from a corrosion pit on the inner diameter surface of the crankshaft bore. Numerous other corrosion pits were found adjacent to the fracture origin. The engine manufacturer reported the engine was built & shipped from the factory on 4/13/81. The engine was the subject of a mandatory service bulletin (S/B), dated 1018/94, that addressed the inspection of the inside bore of the crankshaft for the presence of corrosion. The S/B required that an initial inspection be conducted within the next 200 hrs of operation or 1 year from the date of the S/B. The operator's company manual stated the Director of Maintenance shall ensure that current manufacturer's mandatory S/B's were complied with. No record of compliance with the S/B was noted in the engine maintenance records.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: corrosion and subsequent fatigue failure of the crankshaft, which resulted in engine failure and a forced landing. Factors related to the accident were: the lack of suitable terrain for a forced landing, and the operator's non-compliance with a service bulletin. Full narrative available
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