NTSB Identification: SEA97LA126.
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Accident occurred Tuesday, June 03, 1997 in ADDY, WA
Probable Cause Approval Date: 01/28/2000
Aircraft: Garlick UH-1H, registration: N85NW
Injuries: 1 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
While returning to pick up another log, the pilot heard a high-speed shredding sound' accompanied by high-frequency vibrations. As the noise and vibration increased, the pilot turned downhill and looked for a location where he could make an emergency landing. He then heard a second loud noise, and the rotor RPM immediately began to decay. He stretched his glide over the 130 foot high trees and managed to maneuver the helicopter so that it 'fell into' a switchback on an old dirt logging road. A post accident examination of the K-FLEX drive shaft, which runs between the engine and the transmission, revealed that one of its flex band legs had experienced an inflight fatigue fracture. A review of the records revealed that the shaft had accumulated 459 hours while being used by the United States Army, and had accumulated an additional 432 hours during civilian logging operations.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The inflight failure of the K-FLEX engine-to-gear box drive shaft and no suitable site in which to make a forced/emergency landing. A factor was the mountainous/hilly terrain. Full narrative available
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