NTSB Identification: SEA00LA197.
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Accident occurred Wednesday, August 23, 2000 in NEWHALEM, WA
Probable Cause Approval Date: 07/02/2001
Aircraft: Bell 206BII, registration: N90307
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.
The pilot reported that after landing the helicopter and reducing the engine to idle power, he heard a 'snap' or 'click' above and behind him. The main rotor immediately pitched back and to the left. This violent gyration resulted in the toe of the skids to lift off the ground and the helicopter moved backwards with each pitch up. The pilot shut the engine down. The main rotors windmilled to a stop and the mast came to rest back and to the left about 30 degrees off of vertical. Inspection of the helicopter found that the pylon isolation mount failed. Examination of the mount found that the failure occurred over a long period of time and was probably due to inadequate surface preparation of the center plate to the elastomeric blocks, which resulted in the debonding of the material and allowing the center plate more movement than normal.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: Debonding between the elastomeric material and the center plate of the transmission isolation mount. Full narrative available
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