B737 CREW HAD UNCOMMANDED RUDDER INPUT IN CRUISE. TURNING YAW DAMPER OFF MADE NO DIFFERENCE.

Narrative

AT FL230 CRUISE; ACFT YAWED ABRUPTLY TO L; THEN STAYED IN 'OUT OF TRIM POS' FOR A MIN OR TWO; THEN YAWED ABRUPTLY TO THE R. WE SHUT OFF YAW DAMPER IN ACCORDANCE WITH COMPANY PROCS. UNCOMMANDED RUDDER INPUTS CONTINUED PERIODICALLY FOR REMAINDER OF THE FLT. DECLARED EMER AND LANDED UNEVENTFULLY IN GSO. ENTIRE CREW DID AN OUTSTANDING JOB COORDINATING AND HANDLING THE PAX. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT AFTER LNDG; THE ACFT WAS IMPOUNDED BY THE FAA AND NTSB. IN CONJUNCTION WITH BOEING; ALL APPLICABLE ITEMS ON THE ACFT THAT COULD AFFECT THE INCIDENT WERE REPLACED. THESE ITEMS WERE GIVEN EXHAUSTIVE TESTING; AND NO PROBS WERE FOUND. THE ACFT HAS SINCE FLOWN FOR ABOUT 2 WKS WITH NO FURTHER RUDDER DISCREPANCY NOTED. BOEING HAS TAKEN THE FLT RECORDER FOR ANALYSIS. AT THIS TIME; IT IS NOT YET COMPLETE. THE CAPT FURTHER STATED THAT THE ACFT WAS IN CRUISE AT MACH .76 AT FL230 WHEN THE EVENT OCCURRED. THERE WAS NO MOVEMENT OF THE RUDDER PEDALS. IT TOOK APPROX 50 DEGS OF CTL WHEEL MOVEMENT TO OVERCOME THE RUDDER INPUT. HE DID NOT ATTEMPT ANY FURTHER RUDDER INPUT WITH THE RUDDER PEDALS BECAUSE HE WAS SUCCESSFULLY CTLING THE PROB WITH THE CTL WHEEL. HE DID NOT KNOW WHAT WOULD HAPPEN IF HE TRIED TO USE THE RUDDER. TURNING OFF THE YAW DAMPER MADE NO DIFFERENCE; THE INPUT CONTINUED. THE SKID BALL WAS ALMOST TO THE EDGE OF ITS HOUSING. THE INPUT WAS TO THE L. THE CAPT DID NOT GO TO STANDBY RUDDER; THEREBY SHUTTING OFF EITHER A OR B RUDDER SYS. AFTER A PERIOD OF TIME THE INPUT STOPPED. IN HIS NARRATIVE THE CAPT SAID HE THEN HAD R INPUT. HE NOW FEELS THAT THE RUDDER JUST RETURNED TO NEUTRAL. FOR THE REMAINDER OF THE FLT; THE CAPT COULD FEEL A SLIGHT PULSING IN THE RUDDER PEDALS. THIS PULSING CONTINUED THROUGH LNDG. THERE WAS NO CONVECTIVE ACTIVITY AROUND; NOR WERE THERE ANY OTHER ACFT IN THE VICINITY THAT COULD HAVE UPSET THE ACFT. THE AUTOTHROTTLES WERE OFF; AND THE AUTOPLT WAS OFF AFTER THE INITIAL EVENT. THE CAPT HAS BEEN EXTENSIVELY DEBRIEFED BY THE FAA; NTSB; BOEING AND HIS COMPANY'S FLT AND ENGINEERING PERSONNEL. THE CAPT'S AIRLINE IS ONE WHO IS WIDELY RECOGNIZED AS HAVING AN OUTSTANDING MAINT PROGRAM. THE CAPT HAS OVER 6 YRS EXPERIENCE ON THE B737-200.