On May 15, 1982, a Bell 47G-2 (registration N911X) operated by Island Helicopter, Inc. was involved in an aviation accident near Brookville, NY. Investigators recorded the probable cause as: The No. 6 cylinder intake valve was not seating properly, resulting in low compression and blow-by. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive; 1 related events involving the same aircraft type or operator are linked below.
A helicopter experienced engine and rotor RPM decay while returning to its heliport, prompting a precautionary landing in a plowed field. Investigation revealed a cylinder compression issue due to an improperly seating intake valve.
Event Summary
While returning to the heliport, the pilot observed a decay in engine and rotor RPM. In response, he elected to perform a precautionary landing in a plowed field. During the landing, the manifold pressure reached the red line while RPM continued to decay. The helicopter touched down softly with approximately 10 mph of forward speed. However, the skids dug into the soft ground, causing the helicopter to roll forward and to the right.
Investigation
An investigation into the incident revealed that the No. 6 cylinder had a low compression reading of 5/80, with blow-by evident into the intake system. When the cylinder was removed, the intake valve was found not to be seating properly. No other malfunction or defect of the engine or engine controls was noted.
Probable cause
The No. 6 cylinder intake valve was not seating properly, resulting in low compression and blow-by.