On December 1, 2002, a Bell 47G-3B-1 (registration N48020) operated by Bureau OF Land Managment was involved in an aviation accident near Panaca, NV. Investigators recorded the probable cause as: The intake valve failed between the valve head and the valve stem. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter suffered a loss of engine power and executed a hard autorotation landing, resulting in a severed tail boom. Examination revealed a fractured intake valve in the number 6 cylinder.
Incident Overview
A helicopter experienced a sudden loss of engine power and subsequently performed an autorotation landing. The landing was hard, causing the tail boom to separate from the airframe.
Examination Findings
Inspection of the engine focused on the number 6 cylinder. The intake valve had separated; the valve head was found wedged in the intake valve seat bore. Removal of the rocker box cover on that cylinder showed that the spring retainer had broken into numerous pieces. Additionally, the piston head displayed over 15 impressions consistent in size with the valve head.
Metallurgical Analysis
A metallurgist examined the number 6 cylinder and determined that the valve failed between the intake valve head and the valve stem.
Probable cause
The intake valve failed between the valve head and the valve stem.