Cessna 172N N4773G accident near Rochester, Massachusetts

Probable cause

An engine vibration as reported by the pilot, for undetermined reasons.

NTSB analysis

The pilot reported that the airplane was in cruise flight when the engine developed sporadic engine vibrations. Manipulation of the carburetor heat and mixture controls did not remedy the situation and the engine subsequently developed a severe vibration. The pilot then elected to reduce engine power and perform a precautionary landing to a field. The airplane touched down in a cranberry bog, and sustained substantial firewall and airframe damage. Examination of the wreckage did not reveal any mechanical malfunctions. It was noted that the No. 2 cylinder lower spark plug was fouled and that the compression on the No. 4 cylinder was lower than that of cylinders 1, 2 and 3; however, the reason for the severe engine vibration could not be determined. The airplane had been operated for approximately 74 hours since its most recent 100 hour inspection, which was performed about two months prior to the accident.

Text from the NTSB. Open the NTSB docket for ERA09LA399 for the full record.