The foundation of American’s claims is a phenomenon called aircraft pilot coupling, which is “an unwanted, unexpected and abnormal interaction between the airplane and pilot causing the motion of the aircraft to be out of sync with the pilot’s control inputs.” The airline cites a study done for the NTSB by Dr. Ronald Hess, of the University of California, Davis, which showed the A300-600 rudder-control system to be so sensitive that three pilots, including an Airbus test pilot, were unable to adjust their control movements to deliver a half-travel rudder position during a ground test. According to American, Hess described the rudder-control system on the aircraft as “essentially an ‘on-off’ system, meaning either full rudder deflection or none.” According to The Washington Post, Airbus blamed the pilots for using too much rudder. An A300-600, relative to other aircraft, requires less pressure to move the controls further as airspeed increases. Airbus claims the pilots overstressed the airframe and they further blamed American for not providing proper training in the use of the rudder. American has countered that the rudder on the A300-600 is so sensitive (7.32 times as sensitive as on a Boeing 767 flying at the same speed) that there was no way the pilots could have modulated the rudder action appropriately to prevent the apparent whipsaw effect that may be responsible for loss of the vertical fin and rudder. The APA generally agrees with the airline’s assessment but it also agrees with Airbus that better training could have been provided.
