Primary finding
Probable cause
inadequate overhaul procedures by maintenance personnel resulting in an oil pump failure and subsequent loss of engine power.
Investigator assessment
Analysis narrative
The pilot noted a loss of oil pressure during flight followed by a loss of power. He executed a forced landing, and on final approach the airplane struck a guy wire. The engine oil pump was examined, and the oil pump driven gear had failed due to lack of lubrication. The #3 connecting rod and the camshaft then failed. The engine had been overhauled in the field previously, and a service instruction to increase lubrication of the oil pump driven gear had not been accomplished.
Source record
Factual narrative
On December 30, 1995, about 1025 eastern standard time, N3750H, a Mooney MO20, crashed in Eastover, South Carolina, while on a 14 CFR Part 91 personal flight. Visual meteorological conditions prevailed at the time and no flight plan was filed for the flight. The airplane was substantially damaged and the private pilot received minor injuries. The flight had originated about 10 minutes earlier. The pilot stated he noted a loss of oil pressure followed by a loss of power and he attempted a forced landing to a highway. On final approach the airplane struck a guy wire and came to rest in a ditch. The engine was initially examined by an FAA inspector who removed the engine oil pump and shipped it to the manufacturer's facility for further examination. The oil pump was further examined and it was determined that the oil pump driven gear seized in the accessory housing. It was also noted that when the engine was overhauled in the field, about 1,167 hours earlier, Lycoming Service Instruction 1341 dated July 30, 1976, was not complied with. This service instruction directs that a hole be drilled in the housing to the driven gear, to allow better lubrication. -