Cessna 210 N580TP accident near Arbuckle, California

Probable cause

Insufficient clamping force to the connecting rod bolt, which resulted in looseness in the connecting rod bearing area that led to the fatigue fracture of the connecting rod and a subsequent loss of engine power.

NTSB analysis

During cruise flight, the pilot heard a loud “bang” and immediately observed oil coming from the engine cowling. The pilot subsequently initiated a forced landing and struck trees. A postaccident examination of the engine revealed two holes in the top of the crankcase between the Nos. 1 and 2 cylinders. The No. 2 connecting rod was visibly bent and no longer attached to the crankshaft. The end cap and a section of the yoke were separated and found outside of the engine case.

The No. 2 cylinder piston, pin, connecting rod, and separated sections were sent to the National Transportation Safety Board’s materials laboratory for examination. A materials specialist determined that the damage to the connecting rod was a result of a high-cycle fatigue fracture. The fatigue in the location of the connecting rod would likely occur due to looseness in the connecting rod bearing area due to wear or damage to the bearing, small journal diameter, or insufficient clamping force from the connecting rod bolts. The bearing pieces did not show signs of significant wear and the journal diameter was not known. However, fretting was observed on the clamping surface of the connecting rod cap, which likely indicates that the connecting rod bolt had insufficient clamping force.

Text from the NTSB. Open the NTSB docket for WPR10LA248 for the full record.