What happened
On 9 April 2011, a BAe.ATP aircraft, registration G-MANH, was performing a scheduled night cargo flight from the East Midlands to Cardiff Airport. During the landing sequence on Runway 12, the crew experienced a sudden, intense lateral vibration as the aircraft decelerated through approximately 80 kt. The commander took control of the aircraft and brought it to a halt on the runway to investigate a suspected tyre burst.
Upon inspection, the crew and airport emergency services discovered that the right main landing gear had suffered extensive damage. Both tyres on the right side had deflated, and the sidewalls showed significant tearing and cutting. The incident also caused damage to hydraulic pipes, gear leg components, and the nacelle fairings. There were no injuries to the two crew members on board.
The investigation
AAIB investigators examined the aircraft and recovered metallic debris from the runway, including an apex pin and a castellated nut. The investigation focused on the right main landing gear assembly, specifically the torque link system. It was discovered that the right landing gear had been fitted with a temporary installation of an apex pin following the incident.
Detailed analysis of the recovered components revealed that the threads on both the pin and the nut had been severely weakened by corrosion. This degradation had reduced the effective engagement between the components. Furthermore, the investigation established that the locking bolt, which was intended to prevent the nut from rotating, had suffered a fatigue failure due to repeated mechanical stresses.
Findings
- The primary cause of the landing gear instability was the failure of the threaded joint between the apex pin and the castellated nut.
- Corrosion had significantly reduced the strength of the thread engagement, likely initiated during a period when the aircraft was parked at a saline-heavy environment in the Isle of Man.
- The failure of the locking bolt allowed the castellated nut to move axially along the pin.
- This axial movement resulted in the loss of angular restraint for the axle, causing it to oscillate or 'shimmy' in a horizontal plane.
- The resulting high lateral loads caused the axle to rotate and translate, leading to the destruction of the tyre sidewalls and the deflation of both right-side tyres.