This August 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 Cub. Injuries: None. Location: North Branch, Minn. Aircraft damage: Substantial.
What reportedly happened: The airplane was in cruise flight when the engine started running rough. The pilot turned the ignition key to the off position and executed a forced landing to a field. The fuselage sustained substantial damage during the landing. The inspection of the engine revealed that the number one cylinder connecting rod had failed. The number one cylinder connecting rod bearing was extruded and pieces were found in the oil screen. The bearing exhibited signatures consistent with overheating. About two quarts of oil were found in the engine sump with no signs of external oil leakage. The pilot reported that oil level during the preflight was over four quarts.
Probable Cause: The loss of engine power as a result of oil starvation to the number one rod bearing and number one connecting rod.
For more information: NTSB.gov