Hi!
The basic problem was that Boeing, the FAA, FAA officials, airline officials, airline policy, pilot trainers and pilots all assumed it was OK to make full and abrupt control movements when below a certain speed.
When the very old FAA certification requirements were studied in depth, it turned out that transport category aircraft were NOT certified to withstand a full rudder movment, followed by a complete reversal of the rudder. No one knew this (there might have been a couple of people, but none of the people that mattered) prior to the crash.
Basically, ALL US airline pilots (and I assume all airline pilots) were trained to use the rudder in high angle of attack situations to control the aircraft. At high angles of attack the ailerons become less effective, and the rudder moreso. This is what I learned in the US Air Force.
Emergency notifications were put out after the accident explaining the technical details of the control deflection problem, and pilots are now being trained differently in their simulator situations than they were before the accident.
Cliff
KGRB