Maule M-4-220C N40337 accident near Fredericksburg, Pennsylvania

Probable cause

A total loss of engine power due to the fatigue failure of the No. 4 cylinder piston pin.

NTSB analysis

The pilot reported that, while the airplane was in cruise flight, the engine began to vibrate and lose power. The pilot shut down the engine and performed a forced landing to a field. During the landing roll, the airplane nosed over and was substantially damaged.

Examination of the engine revealed that the No. 4 cylinder head was partially separated and that the No. 4 piston pin was fractured. The piston pin fractured due to fatigue that had initiated at the pin's outer diameter, and the fracture corresponded to the location of the pin bearing separation from the connecting rod. The bearing fracture surface was obliterated. It is likely that pin and bearing wear altered the stress distribution and precipitated the failure.

A review of maintenance records revealed that the 41-year-old engine had been operated for about 1,400 total hours since new and about 50 flight hours since its most recent annual inspection, which was performed about 1 year before the accident. In addition, the No. 4 cylinder was overhauled about 23 years and 560 flight hours before the accident. It was also removed, reconditioned, and reinstalled about 4 years and 165 flight hours before the accident.

Text from the NTSB. Open the NTSB docket for ERA13LA268 for the full record.