What happened
On 9 February 1998, a Hawker Siddeley Aviation HS748 Series 2A, registration G-BPDA, was operating a night cargo flight from Liverpool to Belfast. The aircraft was transporting newspapers when, during the takeoff roll at Liverpool Airport, the left nose landing gear wheel became detached from the aircraft. The wheel was later recovered near the start of Runway 2/27 at the departure airfield.
During the subsequent flight to Belfast, the crew noticed that the 'In-Transit' light for the nose landing gear was slow to extinguish upon gear extension. While the landing gear appeared locked down, the crew sensed a vibration during the landing ground roll, suggesting a possible tyre burst. Upon arrival in Belfast, the absence of the left nose wheel was confirmed. There were no fatalities and no injuries to the two crew members on board.
The investigation
The investigation focused on the components of the nose landing gear axle assembly. Examination of the recovered left hub, axle nut, and outboard bush revealed significant damage. The threads on the axle and the axle nut had been worn away, which allowed the assembly to separate. The investigation also found evidence of severe deformation and wear on the mating faces of the axle nut and the outboard bush, consistent with repetitive hammering and contact.
Furthermore, the investigation identified damage to the edges of the castellation slots on both the axle nut and the bearing adjustment nut. This damage was consistent with the use of incorrect tools, specifically the use of a hook spanner instead of the required tubular spanner and torquemeter. Maintenance records showed that two days prior to the accident, the operator had noted excessive end float and a loose axle nut. Because the correct specialized tools were unavailable, line maintenance personnel had tightened the nut using a hook spanner.
Findings
- The separation of the left wheel was caused by the failure of the axle nut threads due to extreme wear.
- This wear resulted from improper assembly of the axle components, where the bearing adjustment nut was likely not backed off sufficiently before tightening the axle nut, leading to internal hammering and fretting.
- The use of incorrect tools (a hook spanner) during recent maintenance contributed to the degradation of the component edges and prevented the application of the required torque.
- The operator's line maintenance personnel performed an unrecorded adjustment to the axle assembly shortly before the accident.