On January 20, 1994, a Cessna T210N (registration N6191N) was involved in an aviation accident near Hayesville, NC. Investigators recorded the probable cause as: THE FATIGUE FAILURE OF NO. 2 EXHAUST VALVE WHICH RESULTED FROM EXCESSIVE HEAT AND WEAR TO THE VALVE STEM. A FACTOR WAS THE DARK NIGHT. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A pilot reported a complete loss of engine power 30 minutes into flight. A forced landing in an open field followed. Investigation found the number two exhaust valve failed due to fatigue, with evidence of high-temperature degradation and after-market part use.
Event
Approximately 30 minutes into the flight, the pilot reported a complete loss of engine power. While maneuvering for an emergency landing to a public road, the pilot spotted an open field and completed a forced landing.
Examination
Subsequent examination of the engine assembly disclosed that the number two exhaust valve had failed in fatigue at the radius between the valve stem and the valve head.
Metallurgical Findings
Metallurgical examination revealed a decrease in the hardness of the head end of the valve, loss of the chromium plating over much of the length of the valve stem, and excessive wear of the center portion of the valve stem. The valve stem was darkly colored, normally associated with high temperatures, over one half the length of the valve stem. The part number stamped on the exhaust valve corresponded to an after-market supplier's number.