Maule M 7-260C N55000 accident near Oregon, Missouri

Probable cause

Engine vibration for reasons that could not be determined based on the available evidence.

NTSB analysis

The airline transport pilot was conducting a cross-country personal flight. The pilot reported that, after climbing the airplane to cruise altitude and leaning the fuel mixture, he noted an unusual engine vibration. He enriched the fuel mixture slightly, and the vibration seemed to lessen. After descending and increasing power to level off, the engine vibration worsened, and he chose to perform a precautionary off-airport landing. During the landing, the landing gear "dug in," and the airplane subsequently nosed over.

Testing of the engine's fuel system components revealed that the fuel servo fuel flow was slightly richer than the specified service limits. However, according to the pilot's report, the initial engine vibration did not occur until he leaned the fuel mixture at cruise altitude, indicating that the slightly rich calibration of the fuel servo likely was not associated with the engine vibration described by the pilot. Based on the available evidence, the reason for the engine vibration could not be determined.

Text from the NTSB. Open the NTSB docket for CEN15LA170 for the full record.