This January 2008 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 Cherokee. Location: York, S.C. Injuries: 2 Minor. Aircraft damage: Substantial.
What reportedly happened: The airplane was climbing through 4,000 feet when it began to shudder violently and smoke filled the cockpit. The pilot performed a forced landing in a field. The terrain was soft, and the airplane nosed over after coming to a stop.
The post-accident examination of the engine revealed the number two cylinder had separated from the engine crankcase. The through-bolts that attached the cylinder to the crankcase were fractured due to fatigue. There was evidence of welding in the cylinder deck area of the crankcase, which produced a soft condition in the cylinder mounting flanges. This resulted in fatigue fracture of the studs. The engine manufacturer does not allow welding in the critical cylinder deck area of the crankcase. According to the engine maintenance records, the engine was overhauled two years before the accident and had accumulated 679 hours since then.
Probable cause: Loss of engine power due to improper welding of the crankcase, which resulted in fatigue failure of the through-studs and a subsequent separation of the number two cylinder. The unsuitable terrain for a forced landing was also a factor.
For more information: NTSB.gov