NTSB Identification: NYC00LA005.
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Nonscheduled 14 CFR operation of FEDEX
Accident occurred Tuesday, October 05, 1999 in NEWARK, NJ
Probable Cause Approval Date: 07/17/2001
Aircraft: McDonnell Douglas MD-11F, registration: N606FE
Injuries: 2 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

During the landing roll, the center landing gear (CLG) on the MD-11 failed in a rearward direction. The lugs on the upper attach point of the lower drag brace on the CLG failed, the landing gear retraction cylinder was pulled apart, and hydraulic fluid was lost in the #3 hydraulic system. Metallurgical examination of the failed lug found evidence of overload. The DFDR recorded a momentary peak in vertical and longitudinal accelerations, about 5.75 seconds after main landing gear touchdown, and 2.5 seconds after nose wheel touchdown. The vertical acceleration momentarily reduced, and the longitudinal acceleration momentarily increased. According to McDonnell-Douglas, the CLG was capable of entering a divergent, longitudinal oscillation, which could fail the lower drag brace lugs. There were five prior documented events that were identical. After the first three events, McDonnell-Douglas duplicated it twice again, using instrumented airplanes. They subsequently issued a service bulletin for modifications to the CLG brakes and anti-skid system. The accident airplane had these modifications. Additional testing by the operator to determine the loads on the CLG during landing did not find any high loads, and the cause of the CLG oscillation was not determined.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

A divergent, longitudinal oscillation of undetermined origin on the center landing gear, which caused a failure of the center landing gear lower drag brace during landing roll.

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