NTSB Identification: FTW99LA162.
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Accident occurred Wednesday, June 09, 1999 in EUGENE IS. 313
Probable Cause Approval Date: 06/23/2000
Aircraft: Bell 412, registration: N3893S
Injuries: 2 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.
One of the tail rotor blades separated from the helicopter during cruise flight as a result of a fatigue crack. The pilots reported hearing a 'loud bang,' and the helicopter 'immediately and violently tucked down and left then rolled inverted and [was] spinning to the right.' The flying pilot righted the helicopter, and the non-flying pilot inflated the emergency floats prior to impacting the ocean. The outboard section of one of the tail rotor blades (which one could not be determined) was found and examined. A fatigue crack initiated in the spar in an 'area of round-bottomed corrosion pits 0.001 inch deep.' The two tail rotor blades installed on the helicopter had accumulated 4,644 and 4,913 hours, respectively. The tail rotor blades are life limited at 5,000 hours.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The separation of a section of the tail rotor blade, and subsequent separation of the tail rotor system, as a result of fatigue cracking due to corrosion in the tail rotor blade spar. Full narrative available
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