Accident Overview
While maneuvering during mustering operations, the right tail rotor pedal of a helicopter failed and became stuck. The pilot elected to land immediately. During the landing, the helicopter struck a tree, became uncontrollable, and impacted the ground. The accident resulted in substantial damage.
Examination Findings
The tail rotor pedal failed as a result of a fatigue failure at a right angle welded joint between two sections of thin-walled tube. Examination by the Australian Transport Safety Bureau (ATSB) identified that the fatigue failure had initiated adjacent to the weld line, though the exact origin could not be determined. The location of the cracking was coincident with the point of maximum torsional bending stress during normal operation. The microstructure and hardness of the tube and weld were consistent with the requirements specified by the manufacturer.
Maintenance and Inspection
The pedal had undergone a visual examination at the most recent 100-hourly inspection. While it was likely that the crack was present at that inspection, the nature and location of the crack would have made it inherently difficult to detect. The developing fatigue crack would have initially presented as a hairline feature, and it was located on a matte black surface, at a change in section slightly below the level of the cabin floor.