What happened
On 20 June 2020, a Tecnam P2002-JF, registration EC-MOH, operated by FlyBai, was conducting a local dual flight training mission at Burgos Airport. The flight, consisting of an instructor and a student pilot, proceeded normally through various maneuvers before returning to the airport for landing on runway 22. The instructor performed the landing as the student was still in the early stages of training.
During the landing roll, as the aircraft was decelerating, the left main landing gear leg began to fail. The instructor noted intense vibrations and initially believed the issue originated from the nose gear. However, the left landing gear leg eventually detached from the airframe. This caused the left wing and the horizontal stabilizer tip to make contact with the runway. The instructor immediately secured the engine, notified other traffic via radio that the runway was occupied, and ordered an evacuation. Both occupants were uninjured and exited the aircraft without assistance. \n## The investigation
The CIAIAC investigation focused on the structural failure of the landing gear mounting elements. Examination of the wreckage revealed that the left main landing gear had separated from the fuselage. The investigation analyzed the condition of the mounting bolts and nuts, specifically the inner bolt and the two outer bolts.
Technical analysis of the components showed a sequential failure of three elements: the front outer bolt nut, the inner bolt, and the inner bolt nut. The inspection of the front outer bolt nut revealed circumferential scratch marks, which are characteristic of excessive torque being applied during the tightening process. This over-tightening had weakened the nut, leading to the shearing of its threads under axial load. Once this nut failed, the landing gear assembly lost its rigidity, causing an uneven load distribution that subsequently snapped the inner bolt and sheared its corresponding nut.
Findings
- The primary cause of the accident was the detachment of the left main landing gear due to the failure of its mounting assemblies.
- A significant contributing factor was the application of excessive tightening torque on the outer mounting nuts of the left main landing gear.
- The investigation found that while maintenance records indicated torque checks were performed according to the required 50-hour intervals, the physical evidence on the nuts indicated they had been over-tightened, possibly by mistakenly applying the higher torque value required for the inner bolts (25 Nm) to the outer bolts (which require only 15 Nm).
- The aircraft's left main landing gear was found to be more open than the right, suggesting a potential hard landing may have further stressed the already compromised mounting components.