NTSB Identification: LAX98LA184.
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Accident occurred Saturday, June 06, 1998 in BURBANK, CA
Probable Cause Approval Date: 08/03/1999
Aircraft: Aerospatiale AS350BA, registration: N31621
Injuries: 1 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.

The pilot felt a 'violent vibration' and the helicopter began to pitch and yaw. About 5 seconds after the vibration started, the tail rotor gearbox chip light became illuminated. The pilot made a normal approach to a rooftop parking structure and landed. The last 3 feet of the tail boom had separated 360 degrees in circumference. Examination of the tail rotor system revealed one pitch change link disconnected due to a fatigue fracture, which emanated from multiple origins at the inside diameter surface of the loop that is in contact with the bearing assembly. The scrim cloth for the bearing assembly raceway was missing, and the bearing outer raceway contained wear damage approximately 180 degrees around its circumference. A maximum of 0.008 inches of play is allowed in the radial direction between the ball and the pitch change link assembly; however, no limit is specified for the axial direction. The pilot reported that he completed a required daily inspection of the aircraft the day before the accident and observed no play in either tail rotor pitch link, nor did he see any cracks. He also reported that he performed a preflight before takeoff on the accident flight and did not note any discrepancies at that time.

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

The separation of the tail rotor pitch link due to a fatigue fracture, which resulted in the separation of the tailboom.

Full narrative available

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