NTSB Identification: DEN01LA012.
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Accident occurred Monday, October 30, 2000 in MESA VERDE, CO
Probable Cause Approval Date: 05/18/2001
Aircraft: Bell 206L-1, registration: N613
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.

During approach to land on a helipad at the completion of a seeding flight, the helicopter began, what the pilot described as, an unusual vibration. The pilot conducted a normal landing and during inspection following shutdown, the pilot found that one tail rotor blade had shed the trailing edge counterweight and trailing edge skin. He also found that three of the four mounting points for the tail rotor gearbox had fractured. Both tail rotor blades, which had accumulated approximately 30.8 hours since new, were sent to the NTSB Materials Laboratory for examination. The helicopter was repaired and when the shipping container containing new tail rotor blades was opened and the blades unpacked, the repair station rejected one blade for visual abnormalities in the area of the trailing edge counterweight. The rejected blade was also sent to the laboratory for examination. The laboratory examination provided evidence the tail rotor blade failed due to fatigue in the inboard and outboard skins initiating at the root near the trailing edge counterweights. The fatigue initiated due to buckling deformation of the inboard skin, which was found to be thinner than that specified in the manufacturer's drawings. The rejected tail rotor blade examination provided evidence of uneven bonding of the inboard counterweight and deformation due to the riveting process. Deformation was also noted on the outboard counterweight. Composite Structures, LLC, Monrovia, California, manufactured all the tail rotor blades.

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

The manufacturer's use of improper materials, and inadequate quality control of the tail rotor blades during the manufacturing process, which resulted in fatigue failure of the blade.

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