NTSB Identification: FTW02LA021.
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Accident occurred Thursday, October 25, 2001 in Bethany, OK
Probable Cause Approval Date: 07/01/2002
Aircraft: Cessna 152, registration: N67797
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 private pilot reported that during a night cross-country flight, the engine began to lose power. The pilot could not maintain altitude to reach the airport, and therefore, elected to land in a field. The pilot landed the airplane in a field where it impacted a barbed wire fence. An FAA airworthiness inspector examined the engine with the assistance of an aircraft mechanic. The FAA inspector reported that they removed the #2 cylinder's rocker arm cover and noted that "the exhaust valve adjuster 'lock nut' had loosened and come completely off." Review of a maintenance record entry dated May 21, 2000, revealed that the #2 cylinder had been removed, repaired, and reinstalled at an aircraft total time of 825.0 hours. On August 13, 2001, the airplane and engine underwent their most recent 100-hour inspection at an aircraft and engine total time of 1,077.0 hours. The aircraft total time at the time of the accident is unknown. According to the engine operator's manual, persons installing pushrods for a cylinder are instructed to recheck the tappet clearance after run-in and lock the valve clearance adjusting screw in place with the locknut.

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

the mechanic's failure to properly lock the exhaust valve's clearance adjusting screw locknut, which resulted in a loose nut, disabling of the exhaust valve pushrod, and a partial loss of engine power while in cruise flight. A contributing factor was the night light conditions for the forced landing.

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