Cessna 172K N7037G accident near Spartanburg, South Carolina

Probable cause

Maintenance personnel’s failure to follow the engine manufacturer’s maintenance guidance, which resulted in the assembly of the engine with an obstructed oil passage, a subsequent lack of lubrication to the front main bearing, and a total loss of engine power.

NTSB analysis

The pilot was conducting a local “break-in” flight for the airplane’s recently-installed engine. During the initial climb, the engine’s rpm started to decline, followed by a total loss of engine power. The pilot performed a forced landing to a field and the airplane nosed over during the landing roll, resulting in substantial damage to the airplane’s fuselage, wings, rudder, and vertical stabilizer.

A postaccident examination of the airplane revealed that the engine’s crankshaft was not free to rotate. The engine’s front main bearing was discolored and exhibited rotational abrasion at its rear oil passage area and corresponding crankshaft surface. Additionally, insect-related debris, soil/clay/mud, and lubricating oil were obstructing the crankcase oil header and the front main bearing’s aft oil passage. The signatures of lubrication distress observed on the front main bearing were consistent with oil starvation as a result of the obstructions found within the engine’s lubrication system.

Review of the engine’s maintenance records showed that crankcase was repaired nearly 12 years before the accident and that the engine was overhauled 2 years later. The engine did not accrue any time in service prior to its installation on the accident airplane about 1 month before the accident (about 10 years after the overhaul). The mechanic who performed the engine overhaul reported that the crankcase was stored in a hangar for several months before he acquired it and that he did not remember cleaning and verifying that the oil passages of the crankcase were unobstructed before assembly. According to the engine manufacturer’s overhaul manual, all oil passages should be cleaned with suitable brushes then flushed thoroughly with clean solvent and compressed air.

Based on the available evidence, an insect likely infiltrated the crankcase and made a nest in the oil passages during the more than 2 years it was stored. Maintenance personnel then failed to clean and verify the oil passages were free of obstruction before assembly of the engine, which resulted in a lack of lubrication to the front main bearing and a subsequent total loss of engine power.

Text from the NTSB. Open the NTSB docket for ERA24LA388 for the full record.