Incident Details
The airplane was in cruise flight at 4,000 feet mean sea level at night when the pilot reported a partial loss of engine power. Air traffic control provided a vector to the nearest airport, approximately 8 miles north of the airplane's position. About 7 miles from the airport, at an altitude of roughly 1,000 feet, the pilot stated that he would not reach the airport. The airplane subsequently impacted terrain approximately 6 miles from the airport.
Examination Findings
Examination of the wreckage revealed an approximate 4-inch diameter hole on the top section of the crankcase near the number two cylinder. Further examination of the engine at the manufacturer's facility disclosed silicone sealant consistent with RTV along mating surfaces where the cylinders attached to the case. The substance was also found on the through-bolts. The number two cylinder was found backed-off from the case. The engine case exhibited marks consistent with rubbing between the number two cylinder and the case. The number two piston ring had shattered, and the number two piston skirt displayed impact marks consistent with the skirt striking the case. The number two connecting rod showed elongated holes consistent with an overstress failure, and the rod cap was not recovered. The top of the case had two holes in the vicinity of the magnetos.
Mechanic Statement
A mechanic stated that he completed a top overhaul of the airplane engine about 3 months prior to the accident. The overhaul included the installation of six new cylinders. The mechanic reported that he added Permatex RTV (part number 27B) to the cylinder bases during engine assembly. He further stated that he had referred to the manufacturer's service information letter regarding sealants, but it did not list RTV either favorably or unfavorably. The mechanic noted that he did not refer to the manufacturer's service bulletin SB96-7B. That bulletin stated that the use of sealants or lubricants other than those specified by the manufacturer on mating threads and between mating surfaces can cause incorrect torque application and subsequent engine damage or failure.