This August 2009 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Aircraft: Piper Pawnee. Injuries: None. Location: Bainbridge, Ga. Aircraft damage: Substantial.
What reportedly happened: The airplane was performing a training aerial application over a farm when the engine lost power. The pilot performed a forced landing to a field and the airplane hit a tree.
A subsequent examination of the engine revealed that 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 about 12 flight hours ago, the replacement of the magneto could not be correlated to the displacement of the idler gear assembly.
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.
For more information: NTSB.gov NTSB Identification: ERA09LA490