NTSB Identification: SEA00FA061.
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Accident occurred Sunday, April 02, 2000 in STANWOOD, WA
Probable Cause Approval Date: 11/30/2000
Aircraft: Bell 47G-3B-1, registration: N3377H
Injuries: 1 Fatal,1 Serious,1 Minor.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The pilot and two passengers were engaged in a sightseeing flight eastbound over a river in the Bell 47G helicopter when they heard a 'clunk,' the engine began to overspeed, and rotor RPM began to decay. The pilot executed an autorotation to a nearby field. Just prior to touchdown, the helicopter snagged the wires of two low profile, four-foot high electrical fences which he did not see. The helicopter then rolled/yawed to the right and made a hard landing, coming to rest on its right side. Post-crash examination of the engine and transmission revealed no mechanical malfunctions. However, the oil jet (a threaded, hollow plug which screwed into the forward end of the engine crankshaft) was found lying loose beneath the clutch housing. The interior surfaces of the clutch housing displayed a large amount of oil. The clutch assembly was found to be without mechanical disparities and within normal wear limits. The release of the oil jet would have allowed engine oil to flow through the 3/8 inch threaded orifice into the lower transmission and clutch housing at a significantly higher rate than through the small diameter orifice in the end of the oil jet, resulting in disengagement of the clutch. The orifice in the jet was intended to allow a mist or light spray of oil to reach the lower mast bearing for lubrication purposes.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The disengagement of the oil jet fitting from its threaded receptacle at the forward end of the engine crankshaft. This resulted in excessive oil within the clutch assembly, the subsequent slipping of the clutch, and ultimately the disengagement of the rotor drive system from the engine. Contributing factors were the pilot's not maintaining clearance from the electric fences which were also hidden objects against the grass landing surface. Full narrative available
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