NTSB Identification: FTW97LA077.
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Accident occurred Tuesday, December 31, 1996 in RATON, NM
Probable Cause Approval Date: 08/25/1997
Aircraft: Piper PA-28R-201T, registration: N40437
Injuries: 4 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 reported that while in cruise flight the airplane shuddered and began to lose power. She changed the fuel selector from the right to left tank; checked the fuel mixture, the exhaust gas temperature, and the instrument panel. The pilot reported that the engine performance continued to decay and she initiated a forced landing to a pasture. Examination of the engine revealed that the number two cylinder exhaust rocker arm retaining studs had separated. Examination of the studs by a metallurgist revealed that over torquing of the attachment nuts during installation caused plastic deformation of the studs and probable cracking in the threads which led to a fatigue crack in at least one of the studs. The fatigue crack led to the subsequent failure of the exhaust rocker arm retaining studs.

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

failure of the exhaust rocker arm retaining studs due to over torquing of the attachment bolts by maintenance personnel during installation. A factor was the lack of suitable terrain for the forced landing.

Full narrative available

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