On September 16, 1988, a DE Havilland DHC-2 (registration N98JH) was involved in an aviation accident near Mcgrath, AK. Investigators recorded the probable cause as: The failure of an engine exhaust valve, which resulted in a loss of engine power and a subsequent forced landing on tundra. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A float-equipped aircraft experienced an unexplained power reduction while cruising, forcing the pilot to land on tundra where the plane sustained substantial damage due to a failed exhaust valve.
What happened
While the aircraft was in the cruise phase of flight, the pilot-in-command encountered a rough-running engine. This condition eventually progressed to an unexplained reduction of power to idle thrust. The pilot attempted to glide the float-equipped airplane toward a nearby body of water but was unable to reach it. Consequently, the pilot executed a forced landing on the surrounding tundra terrain.
The investigation
Following the accident, investigators examined the engine components to determine the mechanical cause of the power loss. The inspection revealed that an exhaust valve had failed.
Probable cause
The failure of an engine exhaust valve, which resulted in a loss of engine power and a subsequent forced landing on tundra.