11.   Pilots should be trained that such a breakup can occur even at the low speeds that rudder movements had previously been considered safe, the investigators added.

12.   Safety investigators suspect that a sharp rudder movement could explain the Pittsburgh crash but they have not been able to determine what caused the airplane to suddenly roll.

13.   Sudden rudder movement, which could cause the plane to roll and dive toward the ground, is a possibility in both the Pittsburgh and Colorado crashes.

14.   The board instead recommended today that Boeing work with airlines to develop steps that pilots can take to respond to unexpected rudder movements.

15.   The flight data recorder would have picked up any unusual rudder movements.

16.   The investigation might not have taken nearly as long had the flight data recorder measured rudder movement.

17.   The flight data recorders on the USAir, United, Eastwind and Metrojet planes were too primitive to measure rudder movement.

18.   The inquiry panel believes the unwanted rudder movement caused the violent roll.

19.   The NTSB could not say whether the pilots caused the rudder movements or they happened because of a mechanical failure.

20.   The NTSB, meanwhile, also urged the FAA to require additional training for flight crews in dealing with sudden rolls caused by unexpected rudder movement on the airliners.