NTSB Identification: DEN00FA074.
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Accident occurred Tuesday, April 18, 2000 in LAKEWOOD, CO
Probable Cause Approval Date: 04/06/2001
Aircraft: Bell 206L-3, registration: N937S
Injuries: 2 Uninjured.

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.

During initial descent at the completion of a cross-country flight, the pilot heard a loud bang from the rear of the helicopter and manipulation of the tail rotor control became ineffective. The pilot performed an autorotation to a landing in a field, which sloped up about 6 degrees and was rough and uneven. During landing with about 5 knots forward speed, the lower wire cutter dug into the ground and the skids collapsed twisting the cross tubes aft. The main rotor blades were not damaged and the tail booms buckled downward at the forward attach point. The pilot performed a normal shut down and he and his passenger exited the helicopter with no injuries. Examination of the helicopter following the event revealed that both tail rotor blades had separated approximately 9 inches outboard of the hub. Laboratory tests revealed that one tail rotor blade failed from fatigue. The fatigue origin occurred at the protective strip trailing edge inboard of the outboard tip of the blade doubler. Inspection at the origin revealed the fatigue was a result of chemical machining/etching that took place during the manufacturing process.

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

The complete loss of the tail rotor blades due to a fatigue failure of one blade. Factors were sloping and rough uneven terrain for the ensuing forced landing.

Full narrative available

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