Accident Overview
A helicopter transporting passengers to a remote site dropped in a flat attitude and impacted into trees. A witness reported that the helicopter approached and circled the local area. As it flew overhead for the second time, the witness waved his arms to attract the pilot's attention. The helicopter continued past him, and the witness thought the occupants were taking aerial photographs of the site. He noted that the helicopter appeared to be lower and slower on its second pass.
Engine Examination
Post-accident examination of the engine revealed uncommanded engine shutdowns. During bench testing, the power turbine governor failed to limit fuel flow. Disassembly of the governor showed that a machine self-locking hex nut had backed off the muscles valve stem. Further examination of the muscles valve components determined that the threaded valve stem was below the minimum requirements for a UNJ thread, and the flank angle was too large.
Component History
The turbine governor had zero time since overhaul and was installed on the engine in January 1997. It had been last overhauled at the manufacturer's facility during May–June 1996.