The National Transportation Safety Board determines that the probable cause of
this accident was the in-flight separation of the vertical stabilizer as a result of the loads beyond ultimate design that were created by the first officer’s unnecessary and excessive rudder pedal inputs. Contributing to these rudder pedal inputs were characteristics of the Airbus A300-600 rudder system design and elements of the American Airlines Advanced Aircraft Maneuvering Program."
I'm not sure if this has been covered before but a safety award was given for developing that program five days before the accident.
http://www.flightsafety.org/citation...burgh_cit.html