Beech P35 N9777Y accident near Perry, Florida

Probable cause

Maintenance personnel’s incorrect torquing of the oil filter adapter jam nut, resulting in the failure of the adapter threads, a complete loss of oil, and subsequent total loss of engine power.

NTSB analysis

About an hour into the flight, while cruising at 8,500 ft, light smoke entered the cabin momentarily, and the engine oil pressure dropped to zero. The pilot turned toward a nearby airport and shortly thereafter the engine lost power. Unable to glide to the airport, he saw a cleared field and set up for a forced landing. The airplane touched down on sandy soil, the nose gear dug in and separated, and the airframe was substantially damaged. The pilot was not injured.

A postaccident examination of the engine revealed that the oil filter adapter separated at the engine case which likely resulted in a depletion of the engine’s oil supply and the subsequent total loss of engine power due to lack of lubrication. Residual oil covered the area around the adapter-to-engine case opening and below. The adapter threads appeared stripped. The adapter was safety wired in position and there was red torque putty applied as well.

A review of the maintenance logbooks revealed that an annual inspection of the airframe and engine was completed about 29 hours before the accident. The logbook entries noted that an airworthiness directive that addressed security of the connection between the oil filter adapter and the engine case, including checking for proper torque, had been complied with during the inspection. The separation of the filter and stripping of the adapter threads were likely indicative of the oil filter adapter threads having failed due to improper torquing of the jam nut.

Text from the NTSB. Open the NTSB docket for ERA23LA173 for the full record.