What happened
Approximately seven minutes after takeoff, the pilot reported that the engine lost oil pressure and began losing oil, which was followed by a loss of engine power. The aircraft entered a descent that the pilot could not arrest, maintaining a descent rate of approximately 100 to 200 feet per minute. During the descent, the pilot heard a loud bang and felt a shudder in the engine compartment as the engine lost all power.
As the pilot banked the airplane toward a clearing, smoke entered the cockpit and the engine compartment appeared to be on fire. The pilot subsequently elected to perform a forced landing in a field.
The investigation
An examination of the engine at the crash site revealed a hole in the case at the No. 4 cylinder. Investigators observed oil on the No. 4 cylinder wall, noted that the oil dipstick showed no oil, and found evidence of an oil leak from the engine.
A follow-up examination conducted on February 12, 1999, identified that the leak originated at the engine oil filter adapter. During this inspection, investigators noted an uneven distribution of threads on the mounting studs. Using a torque wrench to check the nuts, it was determined that one nut rotated 1.5 rotations before reaching specified torque, while the other rotated only one rotation. Upon removal of the oil filter adapter, a gap of approximately 1/16 of an inch was discovered in the corner of the gasket.
Findings
The investigation concluded that the leak at the oil filter adapter caused the engine to exhaust its entire oil supply. This loss of lubrication led to the failure of the No. 4 cylinder connecting rod, resulting in a total loss of engine power.