Piper PA-25-235 N7339Z accident near Bainbridge, Georgia

Probable cause

A total loss of engine power due to the loss of camshaft timing as a result of the displacement of the idler gear assembly.

NTSB analysis

The airplane was performing a training aerial application over a farm field when the engine lost power and the pilot performed a forced landing to a field, where the airplane impacted a tree. A subsequent examination of the engine revealed that within the accessory section, the idler gear assembly, which normally transferred power from the crankshaft to the left magneto and the camshaft, had been displaced. The short shaft had also been displaced. The mounting plate retaining screws appeared to be sheared. The crankcase surface area around the screw hole exhibited rotational scoring, and the idler gear, located in the oil sump, had no missing or damaged gear teeth. Metal particles were found in the bottom of the crankcase and oil sump. The engine operating time was below the recommended time between overhaul. The failure sequence could not be determined, and although the left magneto had been replaced approximately 12 flight hours prior, the replacement of the magneto could not be correlated to the displacement of the idler gear assembly.

Text from the NTSB. Open the NTSB docket for ERA09LA490 for the full record.