FL-156C N156LZ accident near Upland, California

Probable cause

The pilot’s improper installation of the No. 3 cylinder valve cover, which resulted in an oil leak, oil starvation, and a subsequent total loss of engine power.

NTSB analysis

Shortly after takeoff, the engine lost oil pressure and subsequently lost total power. The pilot maneuvered the airplane to return to the airport, but the airplane touched down in a field and came to rest upright.

Postaccident examination of the engine revealed evidence of an oil leak. The leak likely came from the No. 3 cylinder, as the valve cover was loose, with a gap between the cylinder and the valve cover, which was likely the result of an improperly torqued allen screw. The improper torquing likely occurred during the pilot’s recent inspection of the crankcase throughbolts and re-installation of the engine’s four valve covers. Eventually, the No. 3 allen screw became loose during the engine run-up and continued to loosen during the taxi, takeoff, and climb phases of flight, which resulted in a loss of engine oil and a subsequent total loss of engine power due to oil starvation.

Text from the NTSB. Open the NTSB docket for WPR19LA129 for the full record.