B-737 CREW HAD UNCOMMANDED L RUDDER INPUT.

Narrative

ON DESCENT INTO ORL WE EXPERIENCED A POSSIBLE UNCOMMANDED L RUDDER MOVEMENT. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING INFO: CREW WAS FLYING A B-737-200 ACFT. AT 12000 FT AND 250 KTS; WITH THE AUTOPILOT ENGAGED IN HDG SELECT; THE CAPT NOTICED THE AUTOPILOT HOLDING A SUBSTANTIAL R WING DOWN AILERON INPUT. THE ACFT WAS CROSS CONTROLLED WITH NOTICEABLE L RUDDER. THE CAPT DISCONNECTED THE AUTOPILOT AND GOT A LARGE ACFT KICK AS THE AUTOPILOT WAS NO LONGER HOLDING R AILERON. THE KICK WAS LARGE ENOUGH TO DISLODGE MOST ITEMS IN THE AFT GALLEY. THERE WERE NO INJURIES TO THE FA OR PAX AS EVERYONE WAS SEATED. THE CAPT DID NOT HAVE TIME TO NOTICE THE RUDDER INDICE OR PERFORM ANY EMERGENCY QRH CHECKLISTS. AS SOON AS THE ACFT KICK OCCURRED EVERYTHING RETURNED TO NORMAL; AND NO FURTHER PROBLEMS WERE NOTED. THE CAPT DID NOT KNOW THE STATUS OF THE DIGITAL YAW DAMPER AD; OR WHAT MAINT FOUND. ALL APPROPRIATE PARTIES WERE NOTIFIED AND THE INVESTIGATION IS ONGOING. CALLBACK CONVERSATION WITH REPORTER ACN 457611 REVEALED THE FOLLOWING INFO: RPTR STATED THAT FUEL BALANCE BEFORE; DURING AND AFTER THE AUTOPILOT WAS ENGAGED APPEARED TO BE MATCHED; INDICATING THERE WAS NO NEED FOR A HEAVY WING TRIM. HE FURTHER STATED THAT BASED ON HIS BELIEF AND THE FLYING CAPTAIN'S COMMENTS; THE SUDDEN YAW ACTION COULD HAVE BEEN CAUSED BY A FAULTY YAW DAMPER. HE ALSO STATED THAT THE CLOSEST AIRCRAFT TO THEM AT THE TIME WAS A B737-200; 8.3 MILES AHEAD AND 2600 FT BELOW. THIS INDICATED THE SUDDEN YAW WAS PROBABLY NOT CAUSED BY WAKE TURBULENCE.