NTSB Identification: LAX06LA030.
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Accident occurred Thursday, November 10, 2005 in Rancho Murieta, CA
Probable Cause Approval Date: 04/25/2007
Aircraft: Bell 47D1, registration: N16356
Injuries: 1 Serious.
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 helicopter landed hard following the in-flight separation of the tail rotor assembly. During cruise, the pilot felt a vibration in the anti-torque pedals and attempted to make a precautionary landing in an open field. The tail rotor assembly separated prior to the pilot reaching the landing spot and the helicopter started to rotate and landed hard. The helicopter bounced back into the air, struck the ground again with the transmission bending over the cockpit area. Examination of the tail rotor assembly revealed that one of the pitch change links bolts had separated with the shank portion broken from the threaded portion of the bolt. A metallurgical examination of the bolt revealed that the fracture surface of the shank portion had been subjected to reverse bending fatigue. The arced lines were symmetrical on each side of the shank that culminated in a thin, dark, hourglass-shaped region in the center of the two arced lines. Burnishing observed on the fracture was typical of failures in bolts that have not been properly preloaded.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: a separation of the tail rotor assembly due to the reverse bending fatigue fracture of a tail rotor pitch change link bolt, resulting in a loss of control of the helicopter, and a hard landing during the uncontrolled descent. Full narrative available
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