Piper PA24 N5948P accident near South Boston, Virginia

Probable cause

The powerplant mechanic’s failure to properly affix the engine crankshaft gear lockplate during overhaul, resulting in a total loss of engine power.

NTSB analysis

During a personal flight the private pilot proceeded to the destination airport and entered the airport traffic pattern for a planned full-stop landing. While on a close-in downwind leg of the airport traffic pattern the engine experienced a sudden and total loss of engine power. The pilot turned toward the approach end of the runway and attempted to restore engine power but was unsuccessful. The airplane impacted an obstruction light and touched down in tall grass on airport property before coming to rest upright.

Postaccident examination of the engine revealed the crankshaft gear attachment bolt was loose, the lockplate was fractured, and the alignment dowel was sheared. The intact portion of the fractured lockplate was similar to an un-bent exemplar lockplate; therefore, it is likely the mechanic who overhauled the engine about 253 hours and 8 years earlier did not bend the lockplate against the flat of the crankshaft gear attachment bolt head. The crankshaft gear drives two idler gears in the accessory gearbox, which drive the camshaft, engine driven fuel pump, vacuum pump and the magneto drive couplings. The failure of the crankshaft gear to rotate would result in a loss of engine power.

Text from the NTSB. Open the NTSB docket for ERA20LA195 for the full record.