What happened
On February 7, 2020, a Boeing 757-200, registration TF-FIA, was performing a scheduled passenger flight arriving at Keflavik Airport (BIKF). The flight encountered significant weather challenges, including high winds and turbulence, during its approach to runway 10. The flight crew utilized the ILS for the approach, manually flying the aircraft after the autopilot disengaged due to turbulence at 1,000 feet.
Upon touchdown, the aircraft initially landed on the right main landing gear, followed by the left main landing gear. Immediately after touchdown, an audible metal-fracturing sound was heard, and the right side of the aircraft sank. The right engine subsequently struck the runway. Although the pilot managed to maintain wing level for approximately 12 seconds using aileron and rudder inputs, the right wing eventually slumped again, and the right engine made a second impact with the runway before the aircraft came to a stop. There were no fatalities and no injuries among the 160 passengers and 6 crew members on board.
The investigation
The RNSA investigation focused on the mechanical failure of the right main landing gear. On-site inspections revealed that the attachment of the swivel to the shock strut had detached. Investigators located a missing nut and splined washer near the touchdown zone. Further examination of the landing gear assembly showed that the locking bolt had sheared, with the head and threaded section missing.
Technical analysis of the components revealed that the swivel threads had been undersized during a previous overhaul in November 2019. While the maintenance manual allowed for undersized threads provided a specific mating nut was fabricated, the investigation found that the nut used was too large for the 1/8 inch undersized threads of the swivel. This discrepancy likely prevented the nut from securing the assembly properly.
Findings
- The right main landing gear collapsed due to the failure of the swivel attachment to the main strut.
- The nut and splined washer required to secure the swivel to the shock strut were missing from the assembly.
- The nut used in the assembly was too large for the undersized threads of the swivel, which had been reduced in diameter during a 2019 overhaul.
- The shearing of the locking bolt contributed to the loss of the fastening components.