What happened
On 23 August 2008, a Boeing 747-436, registration G-CIVK, was taxiing toward Runway 27R at London Heathrow Airport for a scheduled passenger flight to Bangkok. During the taxi sequence, the crew of a nearby aircraft observed a fire involving one of the wheels on the G-CIVK and alerted Air Traffic Control. The commander immediately halted the aircraft at Link 23 and requested the airfield fire service.
Upon the arrival of emergency responders, smoke was visible emanating from the No. 7 wheel of the left body landing gear, though no active flames were present. The aircraft's flight data indicated that the tyre pressure sensor signal was lost during the initial turn, and shortly thereafter, the brake temperature for that specific wheel began to rise. Following an inspection, the damaged wheel was removed, and the 293 passengers and 19 crew members were safely disembarked at a terminal stand.
The investigation
The AAIB investigation focused on the physical destruction of the wheel assembly and the maintenance history of the components. Examination of the recovered debris revealed that the wheel hub and axle had sustained extensive damage, including the presence of molten aluminium alloy. The investigation found that the outer bearing cone had fractured into several large pieces, and the inner bearing hub support had been destroyed.
Investigators analyzed the maintenance records for the wheel, noting it had been in service for approximately 11 years and had undergone 26 tyre changes since 1998. The most recent tyre change had occurred just three days prior to the incident. While the technician responsible for the inspection was relatively new to the specific maintenance role, they had completed all required manufacturer training. Flight data from the 134 cycles following the wheel's installation showed no evidence of heavy landings or abnormal lateral loads that could have caused such a failure.
Findings
- The failure originated in the outer wheel bearing, which likely became trapped between the rollers and the rotating hub.
- This mechanical failure caused the bearing to disintegrate, leading to the destruction of the wheel hub and axle.
- Incorrect wheel installation or an inadequate bearing inspection during the last tyre change were identified as the most likely primary causes.
- The investigation could not definitively prove if the axle nut torque was incorrect, but noted that improper torque or failure to rotate the wheel during the seating process could lead to premature wear.
- There was no evidence of fatigue cracking in the wheel hub or significant landing stresses contributing to the event.