NTSB Identification: SEA00LA097.
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Accident occurred Saturday, June 03, 2000 in EUGENE, OR
Probable Cause Approval Date: 05/18/2001
Aircraft: Bell 212, registration: CFHDY
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.
During a practice power recovery autorotation to a hover, at about 600 feet AGL, the two pilots heard a loud bang, followed by a severe vibration. The PIC lowered the collective and rolled both throttles off to continue the autorotation to the ground, which landed without further incident. Inspection of the helicopter revealed that the 90-degree gearbox with tail rotors attached had separated from the tail boom. Inspection of the tail rotors revealed that the tip weight in one of the blades was missing. Examination of the blade revealed evidence of adhesive debonding between the adhesive and the spar surface. As a secondary securing method, four countersunk screws are in line chordwise and offset in pairs on each side of the blade. All four screw holes showed no significant evidence of deformation. It was determined that the four countersunk screws were ineffective due to the limited amount of clamping provided by the machining, at the manufacturer, of too large a diameter in the countersunk hole relative to the diameter of the screw head, thus allowing the four secondary load path screws to slip behind the spar, resulting in the tip block separating from the blade. The manufacturer reported that although the bonding adhesive is identified as the primary securing method for the tip block, and the four countersunk screws as the secondary, either method independent of the other is capable of carrying the load.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: Inadequate quality control by the manufacturer during the manufacturing process, which led to the total failure of a fastener, and the separation of the tail rotor blade balance weight. An adhesive debond between the adhesive and the surface was a factor. Full narrative available
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