Piper PA32RT N27GB accident near Fletcher, North Carolina

Probable cause

A failure of two of the oil pump drive gear’s teeth, which resulted in a loss of engine oil lubrication, and a total loss of engine power.

NTSB analysis

The pilot reported that shortly after taking off, the airplane experienced a loss of engine power so he subsequently performed a forced landing to a parking lot. During the approach to land, he thought the oil pressure gauge was in the “yellow,” and the engine felt like it was “rolling back.” During the impact sequence, the airplane struck a chain link fence, and an electrical distribution box before coming to rest. Much of the airplane was consumed by a postcrash fire.

Examination of the engine revealed that the drivetrain could not be rotated during an attempted rotation by hand of the propeller. Removal of the six cylinders revealed discoloration consistent with lack of lubrication of the connecting rod journals; furthermore, the number four connecting rod was separated from the crankshaft. Removal of the accessories, accessory case, and oil sump revealed that two of the oil pump’s drive gear teeth were fractured. No visible damage was observed to the idler gear which drove the oil pump. Examination revealed the idler gear would not rotate the oil pump drive gear with two separated teeth.

Examination of the oil pump drive gear indicated that the two teeth fractured in overstress under rotation. The direction of bending and shear in the teeth fracture was consistent with the direction of rotation of the gear. Given this information, it is likely that the lack of rotation of the oil pump due to the broken teeth resulted in a lack of lubrication to the engine and the subsequent total loss of engine power. The reason for the failure of the oil pump drive gear teeth could not be determined.

Text from the NTSB. Open the NTSB docket for ERA20LA062 for the full record.