The National Transportation Safety Board (NTSB) is studying whether the rudder deflections following the aircraft's passage through the second wake vortex were produced by pilot input or by another cause. Manufacturing industry experts say that the deflections on their own were not enough to cause the fin to separate unless other factors were involved. The vortices themselves did not produce any lateral loading greater than 0.1g, says the NTSB.

Sources indicate that the acclaimed American Airlines recovery from extreme attitudes training programmes will be studied for a possible tendency to persuade pilots to use too much rudder to counter a wing-drop or accelerate roll. In 1996, Boeing and Airbus published a guide to pilots taking unusual attitudes training which warned of the possibility of overloading an aircraft's structure by using controls as if a large aircraft with a lot of inertia and a tendency to flex were a fighter or trainer.

In 1997, an American A300-600R crew stalled the aircraft by letting the speed decay on entering a holding pattern. A wing dropped and the maximum recorded bank was 56í. The crew's attempts at recovery - eventually achieved - were said by the NTSB to have induced oscillations in pitch, yaw and roll due to a wrong recovery technique.

In 1999, an American A300-600R suffered violent, uncommanded rudder inputs during an approach to Miami. The aircraft later landed safely, but the problem was found to have been a maintenance error involving crossed connections to the autopilot yaw actuator which left the autopilot still engaged to the rudder when disconnect had been selected.


Source: Flight International