JetBlue A320 Incident Due to Induced Fatigue

Air Safety Week, Dec 8, 2008

The failure of an automatic nosewheel centering system on a JetBlue Airways Airbus A320 (N536JB) led to the jetliner's 2005 emergency landing at Los Angeles International, according to a recently-released National Transportation Safety Board (NTSB) report.

The flight, carrying six crew and 141 passengers, had departed Burbank, CA on September 21, 2005 bound for Kennedy International in New York.

Upon retraction of the landing gear, the flight crew noted an error message on the Electric Centralized Aircraft Monitoring system listing a fault message for the nose landing gear shock absorber. Cycling the landing gear then produced an error message of a fault for the nose wheel steering and a subsequent fly-by confirmed suspicions that the nose gear was cocked sideways.

The flight crew diverted to LAX and flew for two hours to burn off excess fuel. The landing shredded the nose gear tires and ground the wheel hubs down to the axle.

Metallurgic analysis of the nose landing gear assembly revealed that two of the four anti-rotation lugs on the nose landing gear upper support assembly had fractured and separated from the upper support assembly. The failed lugs allowed the NLG to deviate from its 0-degree position in the landing gear bay upon gear retraction on takeoff. This resulted in the error message on the ECAM system.

The NTSB report attributed the damage to "induced fatigue from the steering system's programmed pre-landing dynamic steering tests that repeatedly cycles pressure to the steering cylinders."

The National Transportation Safety Board determined the probable cause of this incident to be: "The fatigue failure of two anti-rotation lugs due to repeated cyclic pre-landing tests, which allowed the nosewheels to deviate from the 0-degree position on landing gear retraction. A contributing factor was the design of the Brake Steering Control Unit (BSCU) system logic, which prevented the nosewheels from centering. Also contributing was the lack of a procedure to attempt to reset the BSCU system under these conditions."

Airbus has since issued an engineering bulletin providing a procedure for the flight crew to reset the BSCU in flight, made a design change to the upper support assembly, and provided specific inspection requirements at nose landing gear overhaul.

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