What happened
On 24 December 2019, a Boeing 737-8K5, registration G-TAWG, landed on Runway 23R at Manchester Airport following a flight from Al Massira Airport, Morocco. During the landing roll, as the aircraft slowed to approximately 60 kt, the crew observed an object traveling at high speed along the right edge of the runway. Air Traffic Control subsequently alerted the pilots to a potential tyre issue.
As the aircraft continued to decelerate, the right outer (No 4) mainwheel separated from its axle and moved down the side of the aircraft. The aircraft was able to vacate the runway and come to a halt on a taxiway without further incident. There were no fatalities and no injuries among the 181 passengers or 6 crew members on board. Following the event, the Airport Fire and Rescue Service confirmed that the outer wheel and tyre had detached, causing substantial damage to the associated brake unit.
The investigation
The AAIB investigation focused on the mechanical failure of the landing gear components. Examination of the debris trail showed that the wheel detached approximately 1,800 m from the runway threshold. Physical inspection of the aircraft revealed that the inboard bearing cup had detached from the hub, which had become distorted into an elliptical shape. The damage to the brake pack was extensive, with the torque tube and reaction plate partially detached and the brake pistons fully extended.
Investigators examined the condition of the bearings and found that the inboard bearing had suffered much more severe damage than the outboard bearing. The remains of the rollers showed evidence of overheating and welding. The investigation also reviewed the maintenance history of the wheel assembly, which had been fitted to the aircraft in late November 2019. A review of the tools used during installation revealed that the torque wrench used to apply the preload torque was found to be under-reading by 11% to 12% during a subsequent calibration check.
Findings
- The right outer mainwheel separated from the axle due to the failure of the inboard wheel bearing, which subsequently caused the failure of the outer bearing.
- The severity of the damage to the inboard bearing suggests it may have been operating in a distressed state for some time, generating intense heat.
- The loss of wheel alignment caused the wheel to wobble, leading to the destruction of the bearing rollers and cages.
- The failure of the bearings resulted in excessive loads being transferred to the brake components, causing the torque tube and reaction plate to fail.
- While the torque wrench used during the wheel's installation was found to be out of calibration, the resulting reduction in clamping force was not considered sufficient on its own to cause the failure.