On December 18, 2002, a Schweizer 269C (registration N642KC) was involved in an aviation accident near Los Banos, CA. Investigators recorded the probable cause as: A failed exhaust valve in the number 3 cylinder and the installation of two exhaust spring seats, one on top of the other, resulting in excessive spring and valve pressures. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter experienced a vibration followed by total loss of engine power during a post-maintenance test flight. The pilot performed a forced landing in a muddy field, resulting in structural damage. Investigation revealed a failed exhaust valve and improperly stacked spring seats.
Accident Summary
During a post-maintenance test flight, a helicopter crewed by a commercial pilot and an aircraft maintenance technician experienced a vibration, followed by a complete loss of engine power. The pilot executed a forced landing in a muddy field, during which the helicopter sustained structural damage.
Investigation Findings
Post-accident examination of the engine identified a failed exhaust valve in the number 3 cylinder. Further inspection revealed that two exhaust spring seats had been installed, one on top of the other. This configuration caused excessive spring and valve pressures, which likely contributed to the valve failure. The engine had been overhauled approximately 1.5 flight hours prior to the loss of engine power.
Probable cause
A failed exhaust valve in the number 3 cylinder and the installation of two exhaust spring seats, one on top of the other, resulting in excessive spring and valve pressures.