What happened
On 10 February 2003, a BAe 146-RJ100, registration G-BZAT, was operating a passenger flight from Glasgow to Birmingham Airport. During the takeoff from Glasgow, the crew noted a slight shimmy in the nose wheel, though it did not cause immediate concern. The flight proceeded normally, and due to low visibility at the destination, the crew performed a CAT IIIB autoland at Birmingham.
After the aircraft arrived at its stand and parked, the crew and ground staff discovered that the left nose wheel was missing. The component was later located on the grass approximately 150 metres from the side of Runway 15. There were no fatalities and no injuries to the 5 crew members or 94 passengers on board.
The investigation
The investigation focused on the assembly of the nose landing gear. While the right wheel remained attached, the left wheel had detached from the axle. Examination of the gear revealed that an abutment ring (spacer) had been installed with its chamfered edge facing outward rather than inward.
This incorrect orientation created a gap between the ring and the axle flange. While the wheel retaining nut could still be torqued, the error prevented the two locking bolts from properly engaging with the slots in the axle. Consequently, the nut was not secured. Over time, the rotational forces of the wheel caused the nut to unscrew, allowing the wheel to migrate off the axle.
Maintenance records showed that both nose wheels had been replaced on 4 February 2003, during an outdoor task performed at night in cold, snowy conditions. The engineer involved noted that the abutment ring was already on the axle when the task began, leading them to believe no check of its orientation was necessary.
Findings
- The primary cause of the detachment was the incorrect installation of the abutment ring on the nose landing gear axle.
- The improper placement of the ring prevented the locking bolts from securing the wheel retaining nut.
- Frictional forces during operation caused the unsecured nut to unscrew, leading to the loss of the wheel.
- Environmental factors, including night-time maintenance in cold and snowy conditions, likely contributed to the error.
- The design of the component allowed for incorrect orientation without being immediately apparent during the locking process.