NTSB Identification: CHI00LA277.
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Accident occurred Thursday, August 31, 2000 in SPRING BROOK, WI
Probable Cause Approval Date: 05/18/2001
Aircraft: Bell 47G-2, registration: N67083
Injuries: 1 Uninjured.

NTSB investigators may have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The helicopter impacted the terrain following a loss of tail rotor effectiveness. The pilot reported he just completed a turn in order to begin a swath run when he experienced a loss of tail rotor effectiveness. He attempted to control the helicopter, however it continued to rotate until it impacted the terrain in a clearing in a wooded area. Post accident examination revealed a failure of the tail rotor drive gear assembly. The drive gear shaft was fractured at the underside of the bevel gear. Metallurgical examination revealed fatigue was found over 90 to 95 percent of the shaft cross sectional area. The fatigue cracking origin was on the cylindrical portion of the shaft surface, adjacent to the keyway slot.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

A fatigue failure of the tail rotor drive gear shaft.

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