Incident Summary
On 22 March 2005 at 1140 UTC, a Fokker F27-500 Friendship, registration G-BVOB, operated as a cargo flight, landed uneventfully on Runway 27 at Guernsey Airport. The aircraft executed a 180-degree left turn to back-track the runway. As the commander applied taxi power, a violent shimmy and vibration emanated from the left landing gear. The commander reduced speed and the vibration ceased. Air traffic control reported that the tyres appeared intact but the wheel assembly was oscillating. The aircraft was stopped, the airfield fire service attended, and the engines were shut down. No injuries occurred to the two crew members.
Investigation Findings
Engineering inspection revealed that the torque link centre bolt on the left main landing gear had failed, allowing the torque links to separate. Consequently, the wheel assembly castored about a vertical axis, causing damage to the tyres, wheel rims, and brake components. The head and shank of the failed bolt, along with a castellated nut and debris, were found on the runway. The threaded tail of the bolt was not recovered. Metallurgical examination using a scanning electron microscope showed ductile dimples characteristic of ductile overload across the entire fracture surface. No evidence of fatigue or progressive crack growth was present. The failure was consistent with an axial tensile overload.
Maintenance and Previous Events
The operator's maintenance programme required periodic inspection of the torque link bolt torque loading every C check (550 flight hours or eight months). The last such check was performed on 8 August 2004. The aircraft manufacturer was aware of one previous similar incident in 1991, where corrosion of cadmium plating led to thread stripping and locking pin shear. The 1991 event prompted a recommendation for periodic bolt replacement in high-humidity environments. In the current incident, no corrosion was observed.
Discussion
The investigation was hampered by the non-recovery of the detached bolt tail, preventing confirmation of the locking pin's presence or damage. Despite the nut threads appearing not stripped, they were damaged enough to be ineffective. The overload failure likely occurred as a single event, possibly during the 180-degree turn imposing maximum stress, though earlier failure could not be ruled out. An examination of the brake units from the left landing gear revealed no defects.