Incident Summary
While in cruise flight, the pilot observed a slight vibration in the aircraft and decided to return to the airport. Subsequently, the engine began to shake violently, necessitating an immediate forced landing. The airplane landed short of the intended area, nosed over, and came to rest inverted.
Examination Findings
Post-incident examination of the wreckage revealed that the left rear cylinder on the engine had separated from its mounting flange. The engine had accumulated approximately 13 hours of operation since its last overhaul. During that overhaul, all four cylinders were replaced with chromed cylinders purchased from an outside source, which were then overhauled by the engine overhaul facility.
Metallurgical Analysis
A metallurgical examination of the failed cylinder identified a fatigue origin near the bottom of the fin radius, located between the tenth and eleventh fins from the inboard end of the cylinder barrel. Severe corrosion attack was observed on the fin immediately adjacent to the fatigue origin location. Corrosion damage was also noted in the radius, including a corrosion pit from which crack arrest features appeared to emanate. The corrosion pit was filled with a non-conductive substance.