What happened
During a flight test involving an instrumented McDonnell Douglas MD11, engineers attempted to replicate the specific circumstances of two previous in-service incidents involving center main body landing gear drag link failures. During the landing phase of this test flight, a failure of the drag link was induced. This failure caused the center main body gear to fold aft, resulting in damage to the wheel well and adjacent skin panels.
The investigation
Following the incident, investigators examined instrumentation data from the aircraft. The analysis determined that the drag link failure originated from a dynamic instability of the center body gear. This instability was caused by an unfavorable interaction between the center body landing gear and the brake control system, which included both the anti-skid and auto-brake subsystems.