Narrative:

On descent into orl we experienced a possible uncommanded left rudder movement. Callback conversation with reporter revealed the following information: crew was flying a B-737-200 aircraft. At 12000 ft and 250 KTS, with the autopilot engaged in heading select, the captain noticed the autopilot holding a substantial right wing down aileron input. The aircraft was cross controlled with noticeable left rudder. The captain disconnected the autopilot and got a large aircraft kick as the autopilot was no longer holding right aileron. The kick was large enough to dislodge most items in the aft galley. There were no injuries to the flight attendant or passenger as everyone was seated. The captain did not have time to notice the rudder indice or perform any emergency QRH checklists. As soon as the aircraft kick occurred everything returned to normal, and no further problems were noted. The captain did not know the status of the digital yaw damper ad, or what maintenance found. All appropriate parties were notified and the investigation is ongoing. Callback conversation with reporter acn 457611 revealed the following information: reporter 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.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.