Beech A36 N3600A accident near Abilene, Texas

Probable cause

Maintenance personnel’s improper maintenance of the engine, which resulted in a catastrophic engine failure due the shifting/slipping of the No. 2 bearing and the subsequent oil starvation and total loss of engine power during cruise flight.

NTSB analysis

The private pilot was conducting a cross-country, personal flight. He stated that, upon leveling off at cruise altitude, there was a "severe vibration" coming from the engine compartment, followed by a sound of the engine "coming apart." Oil covered the windshield, and the smoke entered the cockpit. The pilot was unable to return to the departure airport because it was beyond gliding distance, so he performed a forced landing on a field with the landing gear and flaps retracted. The pilot sustained serious injuries.

Postaccident examination of the engine revealed a large hole in the left crankcase half over the No. 2 cylinder attachment point and a small hole in the right crankcase half over the No. 5 cylinder attachment point. The No. 2 main bearing had shifted in the bearing saddle, which cut off the oil supply to the No. 2 rod cap bearing. Shifting/slipping of the bearing can result from either improper torque application during cylinder replacement or improper grinding of the bearing journal during maintenance.

The engine had been disassembled twice before the accident. An engine logbook entry showed that the No. 2 cylinder had been removed and replaced about 328 hours before the accident. It is likely that maintenance personnel did not conduct proper maintenance on the No. 2 cylinder during reassembly of the engine and that this ultimately led to the catastrophic engine failure due the shifting/slipping of the No. 2 bearing and the subsequent oil starvation and total loss of engine power.

Text from the NTSB. Open the NTSB docket for CEN18LA084 for the full record.