Aircraft: Piper Cherokee. Injuries: None. Location: Allentown, Pa. Aircraft damage: Substantial.
What reportedly happened: During the initial climb on an instructional flight, the engine lost partial power. The CFI performed a forced landing into a cornfield.
During a subsequent test-run of the engine, the engine would lose all power if only the right magneto was selected.
Laboratory examination of the right magneto revealed that seven teeth from its drive gear were fractured and exhibited single-sided bending fatigue, consistent with applied force in one direction over a period of time.
At the time of the accident, the engine had accumulated about 2,300 hours since overhaul, which had been completed about seven years prior. The magnetos had not been replaced or serviced since they were installed during engine overhaul.
The engine manufacturer recommended overhauling the engine every 2,000 hours or 12 years, which would have included replacing the magnetos with new or overhauled units. Additionally, a service bulletin issued by the magneto manufacturer recommended inspecting the magnetos every 500 hours; however, there was no evidence that an inspection was ever performed during the 2,300-hour life of the failed magneto.
Probable cause: The failure to perform magneto inspections per the manufacturer’s recommendations and failure to comply with the engine manufacturer’s recommended time interval for engine overhaul, which resulted in defects in the magnetos going undetected and the failure of the right magneto during initial climb.
NTSB Identification: ERA13LA025
This October 2012 accident report is are provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.