What happened
On 17 November 1999, a BAe ATP, registration G-MANH, was performing a public transport flight at Manchester Airport. Following a standard pushback and engine start, the aircraft taxied toward the holding point of Runway 06. Upon receiving clearance from Air Traffic Control to line up on the runway, the pilot attempted to turn the aircraft onto the centreline. During this maneuver, the aircraft began to oscillate violently from side to side.
The pilot immediately halted the aircraft to inspect the main landing gear. Although no obvious external damage was visible through the windows, the crew requested to taxi clear of the runway and contacted company engineers for assistance. During subsequent taxiing, it was noted that the oscillations only occurred during turns and ceased when traveling straight ahead. The passengers were disembarked via buses, and engineers inspected the aircraft on the taxiway.
The investigation
Engineers discovered that the apex pin from the right main landing gear torque links had separated from the assembly. The pin was located on the runway near the centreline, while the nut was found between the runway and the holding point. The locking bolt and its associated nut were missing.
Detailed examination of the recovered pin revealed that the threads were severely worn and distorted in shear at the free end. This distortion indicated that the nut had been stripped from the threads. The investigation established that this was the second such incident for this operator. Previous fleet-wide inspections had already identified several other apex pins with unacceptable levels of wear.
Findings
- The primary cause of the instability was the separation of the right main landing gear torque links apex pin.
- The failure was driven by extreme thread wear and distortion on the pin, which allowed the nut to strip off.
- At the time of the incident, a standardized procedure and specialized tooling for measuring thread wear had not yet been finalized by the manufacturer.
- The operator was operating under interim inspection intervals while awaiting a formal Service Bulletin from the manufacturer.