What happened
On 10 May 2008, a private flight departed from Beverley Airfield in East Yorkshire. After completing necessary pre-flight and power checks, the pilot of the Enstrom F-28A, registration G-BRZG, increased power and raised the collective lever to lift off.
As the helicopter ascended a few feet above its takeoff position, the pilot encountered immediate difficulty maintaining directional control, noting a significant yaw to the left. Attempts to correct this movement using the left pedal were unsuccessful. Fearing a malfunction within the tail rotor system, the pilot reduced power and fully lowered the collective lever. This action resulted in the helicopter rotating through a full 360-degree turn before making a heavy landing on its skids. The aircraft remained in a level attitude upon impact, and the pilot, who sustained no injuries, exited the aircraft via the side door.
The investigation
Following the incident, the aircraft's yaw control system underwent a thorough inspection. A metallurgical examination was performed on several components, including the flexible coupling assembly, by a materials specialist.
Investigators found that one of the tail rotor blades was severely bent and showed marks suggesting it had struck a multi-stranded control cable. However, the cause of this contact remained unclear. Further technical analysis revealed that the tail rotor driveshaft had fractured within the hub of the flexible coupling. The examination of the driveshaft and coupling components, including hardness and elemental analysis, showed no evidence of pre-existing defects.
Findings
- The tail rotor driveshaft failed due to torsional overload.
- The fracture pattern was consistent with the shaft failing in shear because of excessive torque, likely caused by the tail rotor striking an object.
- No pre-existing mechanical defects were identified that could have caused the initial yaw control issues.
- The heavy landing resulted in damage to the skids, the tail rotor, and the tail rotor drive.