What happened
On 22 March 2005, a Fokker F27-500 Friendship, registration G-BVOB, completed a routine cargo landing on Runway 27 at Guernsey Airport. After landing, the crew began a 180-degree left turn to backtrack the runway. During this maneuver, the pilot experienced a violent vibration and shimmy originating from the left landing gear. Believing a tyre had burst, the pilot reduced speed, but air traffic control observed that while the tyres remained intact, the entire wheel assembly was oscillating.
The aircraft was brought to a halt and the airfield fire service was summoned. An inspection of the runway revealed debris from the wheels, including a part of the torque link bolt and a castellated nut. The failure of the gear components resulted in damage to the left landing gear, wheels, and brakes.
The investigation
Investigators examined the recovered portion of the torque link bolt and the castell and nut. Metallurgical analysis using a scanning electron microscope revealed that the bolt failure was a result of axial tensile overload, characterized by ductile dimples and an absence of fatigue or bending evidence.
While the investigation could not definitively confirm the presence of a locking pin at the time of the incident, the damage to the threads inside the nut was consistent with an axial load being applied away from the bolt head. The investigators also noted that the threads in the nut had been severely damaged, though they had not been stripped. The investigation was complicated by the fact that the threaded tail of the bolt and the locking pin were not recovered from the scene.
Findings
- The primary cause of the incident was the failure of the torque link centre bolt due to axial tensile overload.
- The failure allowed the torque links to separate, causing the wheel assembly to move vertically and create an oscillatory action.
- The failure likely occurred during the 180-degree turn, which imposed maximum stress on the component.
- The investigation could not rule out that the failure was triggered by a sudden impact, such as the wheel striking an obstruction, though no such event was recorded.
- The damage to the nut threads suggested that the nut may have moved relative to the bolt, potentially due to frictional forces during landing gear compression.