Event Description
The Boeing 737-300 touched down under the control of the first officer. Immediately after touchdown, the pilots felt a vibration or shimmy. The captain then took control of the airplane and brought it to a stop on the runway.
Examination Findings
Post-event inspection of the right main landing gear revealed that the lower torsion link had failed, allowing the wheels to rotate 45 degrees outboard. A metallurgical examination of the failed torsion link determined that the failure was due to overstress. Additionally, the shaft on the shimmy damper was found bent approximately 20 degrees rearward. The apex nut, which secures the upper and lower torsion links together, was loose on the shaft. The extent of the damage prevented a check of the apex nut for proper torque.
Historical Context
According to a Boeing 737 Service Letter, similar failures of the lower torsion link have occurred previously. These incidents were traced to excessive play at the torsion link apex joint, which rendered the shimmy dampers ineffective. The presence of a loose apex nut and a bent shimmy damper shaft in this event are consistent with that mechanism.