Tail Rotor Shaft Failure Leads to Rotorcraft Loss of Control (N3898Y)

Incident Overview

After taking off to a hover, the pilot executed a pedal turn to prepare for a down canyon departure. Following the turn, the pilot initiated a right slide to clear nearby obstacles. When the rotorcraft had moved laterally approximately 25 feet, the pilot heard a bang. The left pedal immediately became slack, and the rotorcraft began an uncontrolled spin to the right. The aircraft came to rest in a 10-degree nose-down attitude. There were no injuries and no fire.

Investigation Findings

Post-accident examination revealed that the tail rotor shaft assembly had failed between the number 3 and number 4 hanger bearings. Investigators determined that the nuts which hold each assembly together were missing. The bolts were not sheared; one bolt was recovered from the rocks below the tail rotor area, and the other remained in place. No nuts were found at the crash scene. Further inspection showed that the factory-recommended blue dots, which serve as a visual indicator of proper nut torque, were absent on the replacement nuts installed by maintenance personnel.