What happened
On 2 September 2003, an X'Air V2(2), registration G-CBTY, was performing its final hour of a five-hour flight check programme required for the issuance of a Permit to Fly. The flight was being conducted under B conditions at Newtownards Airfield, Northern Ireland.
Following takeoff, the pilot completed three circuits. However, during the final landing on Runway 04, the pilot discovered that the port main wheel was missing. The aircraft had subsequently landed on the brake backplate. The incident resulted in no injuries to the pilot, though the aircraft sustained minor damage to the port brake backplate and the loss of the port wheel and brake drum, which were not recovered.
The investigation
The investigation was based on an incident report from the British Microlseb Aircraft Association (BMAA) and discussions with their technical staff. Upon inspection of the aircraft, it was determined that the wheel retaining bolt had unscrewed from the stub axle.
Analysis of the hardware revealed that the bolt used a standard right-hand thread and lacked a locking mechanism. The pilot noted that the bolt's design allowed it to unscrew while the wheel rotated in a forward direction. Furthermore, the investigation reviewed the BMAA Type Data Sheet for this aircraft model, which specifically warns in its 'Points For Special Attention' section regarding the failure to apply threadlocking compound to wheel hub bolts.
Findings
- The port wheel and brake drum became detached because the retaining bolt unscrewed from the stub axle.
- The bolt was a standard right-hand thread and lacked any secondary locking mechanism to prevent rotation.
- The failure to apply threadlocking compound to the wheel hub bolts, a known issue highlighted in the BMAA Type Data Sheet, contributed to the separation of the component.