Engine Roughness Precedes Forced Landing and Cylinder Head Separation (N6524K)

Incident Narrative

During cruise flight, the pilot reported that the engine began to run rough. Subsequently, the engine blew smoke and oil, and the windshield became covered with oil, obscuring the pilot's forward visibility. The pilot maneuvered the airplane toward the airport. On approach to runway 09, the pilot had no visibility through the oil-covered windshield. During the forced landing, the airplane ran off a road that leads to the runway's centerline and struck an embankment located in the safety area before the approach end of runway 09. The airplane came to rest inverted next to the embankment.

Examination Findings

Examination of the number one cylinder head, which was found separated from its cylinder, revealed no indications of preexisting cracks. The separation occurred in the combustion dome between the cylinder head and the screw-on cylinder barrel. The cylinder head exhibited marks and dents consistent with contact from the piston ring or piston crown.