What happened
On 26 May 2011, a LOT Polish Airlines Boeing 737-45D, registration SP-LLB, arrived at Brussels Airport (EBBR) from Warsaw. Upon touchdown on Runway 25L, the pilot noted a smooth contact with the left main landing gear, followed by a much more violent impact on the right side.
As the aircraft continued its landing roll, the crew experienced steadily increasing vibrations that made the aircraft difficult to control. Simultaneously, air traffic control observed heavy smoke trailing from the aircraft and noted that the plane appeared to be leaning toward the right. The crew eventually brought the aircraft to a stop at taxiway C3. An inspection of the runway revealed debris, including tire chips, metallic fragments, and bolts.
The investigation
The AAIU(Be) investigation focused on the mechanical integrity of the right main landing gear. Examination of the wreckage and flight data revealed severe lateral acceleration of up to 0.6 G starting from the moment of touchdown.
Investigators analyzed the shimmy damper and torsion link assembly. The investigation found that the shimmy damper's upper body had separated from its lower body, with all attaching bolts having sheared off. Furthermore, the lower torsion link of the right main landing gear was found to be broken mid-length and bent downward. The investigation also identified that hydraulic fluid had escaped during the landing roll, coating the flaps and creating the smoke observed by the tower.
Findings
- The primary cause of the instability was the failure of the shimmy damper assembly, specifically the separation of the upper and lower bodies due to sheared bolts.
- The right main landing gear's lower torsion link suffered a structural break.
- The landing gear's vibration was accompanied by significant lateral forces acting on the airframe.
- The visible smoke was caused by hydraulic fluid leaking onto the flaps during the landing roll.