Incident Overview
After leveling at 5,500 feet, the standby power annunciator light illuminated, followed by a loss of oil pressure. The pilot turned the aircraft back toward the airport, but a progressive loss of engine power occurred and the propeller moved to a feathered position. During an emergency landing at night, the aircraft struck a power line and trees before crashing.
Investigation Findings
An engine teardown revealed that disassembly of the reduction gearbox scavenge pump showed a retaining nut and tang washer within the scavenge pump had backed off and lodged between the spur gears. This resulted in a sheared scavenge pump drive shaft. In turn, this led to the loss of oil pressure and allowed the propeller to feather.