NTSB Identification: LAX99LA029.
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Accident occurred Thursday, November 12, 1998 in GILA BEND, AZ
Probable Cause Approval Date: 09/07/2000
Aircraft: Piper PA-28-150, registration: N991PK
Injuries: 1 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 said that no engine discrepancies were noted during either the preflight or the initial cruise portion of the flight, and that all engine instrument readings were normal. Between 500 and 1,100 mean sea level, the engine suffered a significant loss of power accompanied by sputtering, vibration, and the rpm fluctuating. He declared an emergency, performed the emergency checklist with no changes, and made a forced landing on a road. During the landing rollout the airplane struck a road sign that he had not seen. Postaccident inspection of the engine revealed the gear at the back of the crankshaft was detached and moving freely between the corresponding gears. The crankshaft gear attaching bolt and threads were undamaged and the bolt appeared to have backed out of the crankshaft and was resting in the crankshaft gear bore. The bolt locking plate remained at the head of the bolt, and exhibited fretting signatures. Fretting signatures were also located around the mating surfaces of the gear and crankshaft bore. The crankshaft gear dowel pin had failed, with fatigue striations visible to the naked eye. An engine overhaul was completed 1 month after an airworthiness directive (AD) was published requiring inspection of the crankshaft gear and the bolt to prevent the bolt from backing out and liberating the crankshaft gear. No evidence of compliance with this AD was found in the engine maintenance records.

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

The crankshaft gear attach bolt loosening and backing out of its crankshaft bore, which led to the fatigue failure of the crankshaft gear dowel pin due to excessive working of the gear. The sequence of failures was the result of the engine overhaul shop's failure to comply with an Airworthiness Directive and the engine manufacturer's Service Bulletin.

Full narrative available

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