What happened
During mustering operations, a helicopter experienced a mechanical failure when the right tail rotor pedal became stuck. In response to the failure, the pilot attempted an immediate landing. During this emergency manoeuvre, the aircraft struck a tree, leading to a loss of control. The helicopter subsequently impacted the ground, resulting in substantial damage to the airframe.
The investigation
Investigators examined the components of the tail rotor pedal and identified a fatigue failure at a right-angle welded joint connecting two sections of thin-walled tubing. While the investigation confirmed that the fatigue crack initiated near the weld line, the precise origin of the failure could not be established. This specific area of the component is subject to the maximum torsional bending stress during standard operations. Testing of the tube's microstructure and hardness confirmed that the materials met the manufacturer's original specifications.
Technical analysis also reviewed the most recent 100-hourly inspection. Although the crack was likely present during that maintenance period, its location and characteristics made it extremely difficult to identify. The crack began as a hairline feature situated on a matte black surface, positioned at a section change just below the cabin floor level.
Findings
- A fatigue crack developed adjacent to a weld at a high-stress point on the pedal.
- The fatigue failure of the right tail rotor pedal was the primary driver of the mechanical malfunction.
- The physical location and the matte finish of the component likely hindered the detection of the crack during previous inspections.