What happened
On March 5, 2013, an ATR 72-212 A, registration F-GVZL, operated by Airlinair, was taxiing after landing on runway 14 left at Toulouse-Blagnac. During the taxi phase, the crew heard a noise accompanied by vibrations originating from the nose gear. As the pilot attempted to turn left toward the parking apron, the nose gear steering became non-functional. The aircraft continued braking until a second noise was heard, at which point the aircraft came to a halt on the runway centerline.
The investigation
The investigation focused on the structural integrity of the nose gear assembly. Investigators found that the two halves of the nose gear linkage (the torque links) had become separated because the connecting pin was missing. This failure caused the nose gear to pivot sharply to the right, resulting in the tires pulling out of their rims. The proximity switch housing was also detached and hanging by its wiring, with visible impact damage to the nose gear strut from repeated strikes.
While some components, including a washer and part of the mounting hardware, were recovered approximately 1,000 meters from the runway threshold, several other parts of the linkage assembly could not be located. Metallurgical analysis of the remaining parts revealed advanced corrosion on the threaded portion of the connecting pin, with corrosion depths reaching approximately 0.3mm. The analysis also noted significant damage to the threads, suggesting the nut or other assembly elements had receded or shifted.
Findings
- The primary cause of the separation was the loss of the connecting pin during taxiing.
- Severe corrosion on the threaded section of the pin likely weakened the mechanical integrity of the bolt and nut assembly.
- The degradation of the threads and corrosion deposits may have prevented the proper installation or secure tightening of the nut.
- Maintenance records indicated that the same pin had been in service since 1998 and had accumulated over 26,000 flight hours and 34,000 cycles.
- Previous maintenance tasks, including a shock absorber replacement in April 2012, did not require the replacement of the pin or the inspection of its condition, and the components were likely reinstalled in their existing state.