What happened
On 4 May 2018, a Cessna 525C – CJ4, registration EC-MOQ, operated by Aluminios Cortizo, was performing a private flight from Zagreb to Santiago de Compostela. The landing on runway 35 was initially uneventful, with the aircraft touching down at a slightly nose-down attitude.
As the crew began a left turn to vacate the runway via taxiway E3, the aircraft leaned to the left. The crew initially suspected a flat tire, but the left main landing gear leg subsequently collapsed, causing the left wing to dip and the aircraft to come to a stop on the runway. There were no injuries among the two crew members and four passengers on board.
The investigation
The CIAIAC investigation focused on the mechanical failure of the landing gear assembly. Examination of the wreckage and components revealed that the left main gear leg had moved outside its extension-retention axis.
Investigators analyzed the trunnion pins and bolts of both the left and right landing gear legs. The inspection of the left leg showed that the bolt attaching the aft trunnion pin to the trunnion had been installed incorrectly. This error allowed the trunnion pin to shift toward the rear, eventually decoupling from the trunnion and causing the leg to collapse. Interestingly, the investigation found that the right landing gear leg also had an incorrectly installed bolt, though the pin remained in position and did not fail during this event.
Findings
- The primary cause of the collapse was the improper installation of the bolt in the aft trunnion pin, which permitted the pin to move within the trunnion fitting.
- The incorrect installation had persisted for approximately 414 flight hours and 193 landing cycles.
- Evidence suggested that the components had been correctly installed at some point in the past, implying the error occurred during a subsequent maintenance task.
- The investigation identified several other maintenance non-conformities, including the use of an incorrect part number for a forward trunnion pin on the left side.
- The maintenance facilities involved lacked sufficiently standardized procedures or oversight to ensure the correct application of installation tasks for critical landing gear components.