What happened
On September 13, 2006, a Fokker F 28 MK 100 arrived at Frankfurt/Main from Paris, carrying 88 passengers and five crew members. The aircraft landed on runway 25L at approximately 19:41 local time. The landing was initially described by the crew as a smooth touchdown.
During the rollout, at a speed of approximately 100 kt, the crew noticed moderate vibrations. While the pilot initially suspected a tire burst, the vibrations quickly intensified, affecting the main landing gear. The pilot then utilized emergency reverse thrust to bring the aircraft to a halt. During the deceleration, an air traffic controller reported observing smoke near the main landing gear area. The aircraft eventually came to a stop on taxiway Hto. There were no fatalities and no injuries were reported, though the aircraft sustained heavy damage.
The investigation
Following the incident, investigators located four metal fragments from the left main landing gear on the runway. Upon inspection of the aircraft, the eye of the upper torque link connection on the left main gear was found to have suffered a forceful fracture. The hydraulic reservoir of the shimmy damper was also found to be coated in hydraulic fluid.
Detailed examination of the shimmy damper revealed several critical issues. The O-ring between the damper housing and the cap was improperly installed, partially pinched in the groove. Furthermore, the thread insert in the damper housing had been installed crookedly. The investigation also found that the torque required to loosen the mounting bolts was significantly higher than the prescribed limits, suggesting they had been over-tightened. Additionally, traces of a gel-like substance and a small metal chip were discovered inside the damper mechanism, which hindered its performance.
Findings
- The primary cause of the accident was the failure of the shimmy damper to provide adequate damping, which led to the structural failure of the torque link.
- The failure was caused by a combination of an improperly installed O-ring and internal contamination, including a metal chip and foreign substances.
- It is likely that these contaminants entered the unit during its recent overhaul.
- The maintenance facility's documentation indicated that while some tests were performed, the flow test results were not recorded, and the facility was using outdated testing criteria that did not meet the current manufacturer requirements.