NTSB Identification: SEA97LA152.
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Accident occurred Thursday, June 26, 1997 in OGDEN, UT
Probable Cause Approval Date: 01/28/2000
Aircraft: Cessna 172A, registration: N6844X
Injuries: 1 Minor,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.

About 30 minutes after takeoff, the engine began to run rough and lose power. The first pilot (pilot-in-command) attempted to regain full power and return to the departure airport. The airplane continued to descend and the first pilot attempted to land in a hayfield about four miles from the airport. During the forced landing, which occurred in a tailwind, the pilot noticed power lines ahead. He forced the airplane onto rough terrain beneath the power lines. The airplane nosed over on landing and was substantially damaged. An examination of the engine revealed that the exhaust valve stem on the no. 4 cylinder had separated from the valve head. The fracture surface was obliterated and the mode of failure could not be determined. After the failure of the valve, further damage to other cylinder components subsequently occurred as the engine continued to operate in a degraded condition. The no. 4 cylinder had been reworked about 108 flight hours prior to the accident.

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

The fracture of the no. 4 exhaust valve and subsequent loss of engine power. Factors contributing to the accident include a congested landing area, and rough terrain.

Full narrative available

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