What was found
AIRCRAFT LANDED UNDER AMBER ALERT AFTER REPORTING UNCOMMANDED RUDDER MOVEMENT ON TAKEOFF. A UPDATE FROM THE FDR DATA, IT DOES NOT APPEAR THAT ANY FLIGHT CONTROL SYSTEM INITIATED THE EVENT. THE DATA DOES SUGGEST THAT THE INITIAL UPSET COULD HAVE BEEN INDUCED BY AN ATMOSPHERIC DISTURBANCE. THE RUDDER PCU AND THE YAW DAMPER COUPLER WERE REPLACED. THERE WERE NO FAULTS FOUND WITH THE RUDDER PCU. THE YAW DAMPER COUPLER IS STILL BEING CHECKED.