NTSB Identification: FTW00LA107.
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Accident occurred Friday, March 24, 2000 in MAUD, OK
Probable Cause Approval Date: 07/17/2001
Aircraft: Cessna 172N, registration: N75958
Injuries: 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 flight instructor and private pilot receiving instruction were practicing basic maneuvers, during an instrument training flight, when the airplane began to 'vibrate violently.' They retarded the throttle, checked the magnetos, and then performed a precautionary landing to an open field. During the landing roll, the right horizontal stabilizer impacted a fence. An FAA inspector reported that the #3 exhaust rocker arm retaining stud separated. A section of stud was found lodged beneath the intake rocker arm, and the remaining portion of the stud remained seated in the cylinder head assembly. Metallurgical examination revealed that the stud failed due to fatigue that originated at the thread root from multiple origins.

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

the loss of engine power while maneuvering as a result of the separation of the exhaust rocker arm retaining stud due to fatigue, which resulted in a precautionary landing.

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