Cessna 170 N5478C accident near Baker City, Oregon

Probable cause

The failure of the No. 2 connecting rod bearing as a result of oil starvation due to a contaminated oil filter screen.

NTSB analysis

The pilot reported that during a local flight, the engine started to knock and vibrate, and the oil pressure indication was low. He initiated a precautionary landing to an open field, and during the landing rollout, the airplane impacted a small ditch, which resulted in substantial damage to the left wing.

A postaccident examination of the engine revealed that the No. 2 connecting rod was separated from the crankshaft. The No. 2 connecting rod journal exhibited thermal distress and mechanical damage. The remaining connecting rod journals and the crankshaft main bearings also exhibited thermal discoloration consistent with oil starvation. When the engine was rotated, no oil flow was observed through the crank journals and lifters. The oil filter screen was covered in dark thick oil and metallic debris and was collapsed.

It is likely that the contaminated oil filter screen collapsed under pressure from the oil pump, which prevented the normal flow of oil through the engine; this resulted in the oil starvation of the No. 2 connecting rod bearing and subsequent separation of the connecting rod from the crankshaft.

Text from the NTSB. Open the NTSB docket for WPR20LA097 for the full record.