21.   The most controversial proposal involved whether Boeing should have to develop operational or design changes to reduce the possibility of unexpected rudder movements.

22.   The power control unit, which operates similarly to power steering in a car, converts rudder pedal movement from the cockpit into hydraulic power to move the rudder.

23.   The safety panel heard separate testimony Wednesday that contaminated hydraulic fluid and wake turbulence created by another aircraft could have contributed to the inadvertent rudder movement.

24.   The swings corresponded to rudder pedal movements in the cockpit, investigators said.

25.   There is not supposed to be any rudder movement a pilot can command that will rip off the tail.

26.   Use of that technique might explain the sudden large rudder movements that were recorded in the last seconds that the flight data recorder operated, according to aviation experts.

27.   WASHINGTON--Sharp rudder movements on an airplane during flight may damage the tail enough to cause an accident, officials from the National Transportation Safety Board said Friday.

28.   The Airbus twice hit wake turbulence before it started veering from side to side with sharp rudder movements.

29.   The board is investigating the rudder movements.

30.   The National Transportation Safety Board also urged additional training for flight crews in dealing with sudden rolls caused by unexpected rudder movement on the airliners.