Fatigue Caused By Normal Cyclic Pre-Landing Tests

The failure of an automatic nosewheel centering system on a JetBlue Airways Airbus A320 led to the flight's 2005 emergency landing at Los Angeles International Airport, according to a National Transportation Safety Board report.

The flight, carrying six crew and 141 passengers, departed Burbank, CA on September 21, 2005 bound for JFK airport 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," the report said.

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.

As ANN reported, the flight crew elected to divert to LAX and flew for about two hours to burn off excess fuel. Although the landing shredded the nose gear tires and ground the wheel hubs down to the axle, the landing was otherwise uneventful. The plane tracked straight down the runway and no injuries were reported.

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 other two lugs contained cracks."

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."

Adding to the problem was the operation of the Brake Steering Control Unit which tried to re-center the nose gear, but shut the steering system down when a second fault was detected. "Also contributing was the lack of a procedure to attempt to reset the BSCU system under these conditions," the NTSB said.

Airbus has since issued an Operations 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.

FMI: www.ntsb.gov, www.airbus.com, www.jetblue.com