Background
McDonnell Douglas conducted a flight test of an instrumented MD11 to investigate two previous in-service incidents involving failures of the center main body landing gear drag link. The test protocol was designed to replicate the known circumstances of those failures.
Test Flight
During the landing of the test flight, a failure of the drag link was induced. The failure allowed the center main body gear to fold aft, causing damage to the wheel well and adjacent skin panels.
Findings
Examination of the instrumentation data revealed that the drag link failure was the result of a dynamic instability of the center body gear. This instability was due to an unfavorable interaction between the center body landing gear and the brake control system, including the anti-skid and auto brake subsystems.
Corrective Action
As a corrective action, the manufacturer developed a modification to the anti-skid control unit.