Airbus's structural testing shows that forces on fin of American A300-600R exceeded design limits on attachment lugs

Structural testing conducted by Airbus for the US National Transportation Safety Board indicates the composite fin sheared off the American Airlines A300-600R that crashed in November 2001 because loads on the tail exceeded the design ultimate limit of the attachment lugs. The NTSB has examined the flight-control system and pilot/aircraft coupling, but has not concluded whether abnormal loads on the tail were a result of a rudder anomaly or pilot action.

In its latest update on the investigation into the crash of flight 587 into Belle Harbor, New York, which killed all 260 people on board, the NTSB says the structural test was conducted at the Airbus facility in Hamburg, Germany, in August. A rear main attachment lug from an A310-300 carbonfibre fin-box skin panel was subjected to a load condition derived from the accident aircraft's flight data recorder and subsequent structural finite-element analysis. The load was beyond the design ultimate limit, and the lug failed. The test failure appeared consistent with failure load analyses by both Airbus and NASA, says the NTSB.

For certification, design ultimate load must be at least 1.5 times the highest load expected to be encountered in service. The skin panel used for the test was originally produced as a manufacturing quality test article, and the test suggests the fin as designed has adequate strength margin under normal loads. The NTSB plans to test two other rear lugs removed from the fin of an American Airlines A300-600R that was involved in a loss-of-control incident in 1997. The first will be tested in December and the second in February next year.

The NTSB has completed examination of the flight-control cable routing for possible failure modes that could have led to the accident, and has also examined the design of the A300-600's rudder limiter. Other areas examined include the directional stability and control of the A300-600, pilot/aircraft coupling design issues, aircraft response to differing rudder designs and checking the service history of the Airbus aircraft for high tail-load events that might involve issues related to the accident.

Source: Flight International