Cessna P210N N3599P accident near Leavenworth, Washington

Probable cause

The failure of the number two cylinder exhaust and intake valves for undetermined reasons, which resulted in a loss of engine power.

NTSB analysis

The airplane was in a cruise flight configuration when the engine ceased operating without warning. The pilot made an emergency descent and the airplane collided with a fence while landing in a field. Disassembly of the engine revealed extensive mechanical damage to the number two cylinder combustion chamber and piston assembly. The exhaust valve seat insert was missing and fragments of the insert were later found in the oil sump. The exhaust valve head had separated from the valve stem. The intake valve head had approximately 50 percent of the material separated. The fracture surfaces on the exhaust valve, intake valve and exhaust valve seat were damaged such that the mode of fracture could not be definitively determined. Hardness testing of the components indicted that they were within the manufacturer’s prescribed specifications. The sequence of fractures and separations of components could not determined.

Text from the NTSB. Open the NTSB docket for WPR10LA196 for the full record.