Columbia Aircraft Mfg LC41 550FG N8725 incident near Chandler, Arizona

Probable cause

The over-tensioning of the accessory belt, which resulted in damage to the starter adapter and subsequent loss of oil that led to oil starvation and catastrophic engine failure.

NTSB analysis

During the flight the pilot reported a loss of oil pressure followed by a decrease in manifold pressure. The pilot declared an emergency and requested landing clearance, however, the engine lost total power and he initiated a forced landing to a field where the airplane sustained minor damage. Postincident examination of the airplane revealed that the lower side of the fuselage was covered in oil and a hole was discovered in the engine’s crankcase. The examination of the engine revealed damage to the starter adapter assembly, which included the starter pulley, bearing, seal, and shaft, that was consistent with the over-tensioning of the accessory belt, which resulted in an excessive side-load. The damaged starter adapter assembly components ultimately resulted in the loss of engine oil and subsequent failure of several connecting rods due to oil starvation. A manufacturer Critical Service Bulletin provided instructions for an inspection of the starter adapter for indications of oil leakage at the shaft oil seal, however, review of the airplane maintenance records show that the service bulletin was not complied with.

Text from the NTSB. Open the NTSB docket for WPR17IA173 for the full record.