YUMA, AZ, USA
N90187
McDonnell Douglas MD-11
MCDONNELL DOUGLAS INSTRUMENTED A FLIGHT TEST MD11 TO EXPLORE TWO PREVIOUS IN SERVICE INCIDENTS OF CENTER MAIN BODY LANDING GEAR DRAG LINK FAILURES. THE TEST PROTOCOL WAS DESIGNED TO REPLICATE THE KNOWN CIRCUMSTANCES OF THE TWO IN SERVICE FAILURES. DURING THE LANDING ON THE TEST FLIGHT, A FAILURE OF THE DRAG LINK WAS INDUCED, WHICH ALLOWED THE CENTER MAIN BODY GEAR TO FOLD AFT DAMAGING THE WHEEL WELL AND ADJACENT SKIN PANELS. EXAMINATION OF THE INSTRUMENTATION DATA REVEALED THAT THE DRAG LINK FAILURE WAS THE RESULT OF A DYNAMIC INSTABILITY OF THE CENTER BODY GEAR DUE TO AN UNFAVORABLE INTERACTION BETWEEN THE CENTER BODY LANDING GEAR AND THE BRAKE CONTROL SYSTEM (INCLUDING THE ANTI SKID AND AUTO BRAKE SUB SYSTEMS). AS A CORRECTIVE ACTION, THE MANUFACTURER DEVELOPED A MODIFICATION TO THE ANTI SKID CONTROL UNIT.
AN UNSTABLE INTERACTION BETWEEN THE CENTER BODY MAIN LANDING GEAR AND THE BRAKE SYSTEM.
Source: NTSB Aviation Accident Database
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