Incident Details
An airplane conducting a traffic observation flight experienced a total loss of engine power. The pilot performed a forced landing to a schoolyard and was uninjured.
Engine Examination
Initial examination of the engine revealed heat damage to the #4 cylinder and a complete absence of oil. Removal of the #4 cylinder showed a hole in the #4 piston at the 12 o'clock position beneath the piston ring lands, extending through to the interior of the piston. Additionally, a deep groove was found on the side of the #4 piston in line with the forward piston pin plug. The plug was worn and heat damaged with significant material loss, and material transfer from the plug was observed on the wall of the #4 cylinder.
Further disassembly revealed that the #1 connecting rod was separated from the crankshaft upon removal of the #2 cylinder. Examination of the piston rings found that the oil-scraper rings on the #1 and #2 pistons had been installed backwards. Additionally, three base nuts on the #3 cylinder were installed upside down.
The #1 and #2 cylinder assemblies were identified as Superior cylinders, while the #3 and #4 assemblies were reworked Lycoming cylinders. The individual piston part numbers could not be determined.
Maintenance History
Review of maintenance records showed that the owner/operator replaced the #3 and #4 cylinder assemblies 337 aircraft hours prior to the incident. At that time, the engine was serviced with 80 weight oil and returned to service. The #1 and #2 cylinder assemblies were replaced by a maintenance facility 235 aircraft hours prior to the incident, and the engine was serviced with mineral oil as recommended by the engine manufacturer.