THIS ACR B737-200 FLC EXPERIENCED AN UNCOMMANDED RUDDER DISPLACEMENT THAT CAUSED THE ACFT TO ROLL TO THE R. INITIALLY; THE FLC WAS UNABLE TO OVERPOWER THE UNCOMMANDED INPUT; BUT WERE ABLE TO MAINTAIN APPROX LEVEL FLT BY XCTLING THE ACFT.

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FLT FROM MCO TO BDL. 33000 FT .67+ MACH NORMAL CRUISE. EXPERIENCED UNCOMMANDED ROLL TO R. FIRST NOTED BY DISPLACEMENT OF CTL WHEEL TO L WITH NO PLT INPUT. TOOK CTL OF ACFT; NOTED THAT RUDDER PEDALS DISPLACED TO R; R RUDDER FORWARD AND UNABLE TO CTR. MAINTAINED CLOSE TO LEVEL FLT WITH CONSIDERABLE L AILERON INPUT. DECLARED EMER; COMPLIED WITH PROCS IN QRH; BOTH PLTS COULD NOT CORRECT RUDDER. WHEN 'B' SYS HYD SWITCH PLACED TO STANDBY RUDDER; RUDDERS CTRED AND CONTROLLABLE. DURING APCH NOTED VIBRATION IN RUDDER PEDALS AND SOME RUDDER 'KICKS.' UNEVENTFUL LNDG BWI; RWY 33L. MADE APPROPRIATE LOGBOOK ENTRY. SUPPLEMENTAL INFO FROM ACN 429548: I DECLARED AN EMER WITH ATC. IMMEDIATE ACTION ITEMS CONSISTING OF AUTOPLT; AUTOTHROTTLES AND YAW DAMPER WERE TURNED OFF. BOTH PLTS ATTEMPTED TO MOVE JAMMED RUDDER PEDALS. NO DESIRED MOVEMENT OBSERVED. QRH PROCS COMPLIED WITH. RUDDERS WERE FREED UP WHEN 'B' SYS HYD SYS FLT CTL SWITCH WAS PLACED TO STANDBY RUDDER POS. CALLBACK CONVERSATION WITH RPTR ON ACN 429547 REVEALED THE FOLLOWING INFO: THE RPTR SAID THAT THE CAPT WAS FLYING THE ACFT ON AUTOPLT AT THE TIME OF THE RUDDER DISPLACEMENT AND THE RPTR ATTEMPTED TO ASSIST WHEN THE R RUDDER PEDAL WENT; FULL TRAVEL; FORWARD. THEN AS THE FLC STARTED THROUGH THEIR UNCOMMANDED RUDDER INPUT CHKLIST THIS RPTR ASSUMED CTL OF THE ACFT. THIS RPTR HAS SPOKEN TO MAINT PERSONNEL AND THEY HAVE BEEN UNABLE TO DISCOVER THE CAUSE FOR THE RUDDER DISPLACEMENT. THE ACFT HAD ONE OF THE NEW RUDDER CTL VALVES INSTALLED AND IT WAS IN PROPER WORKING ORDER ACCORDING TO MAINT. CALLBACK CONVERSATION WITH RPTR ON ACN 429548 REVEALED THE FOLLOWING INFO: THIS RPTR SAID THAT WITH BOTH FLC PUSHING ON THE OPPOSITE RUDDER PEDAL THEY WERE UNABLE TO CORRECT THE R RUDDER DISPLACEMENT. HOWEVER; HE WAS ABLE TO MAINTAIN LEVEL FLT BY USING ALMOST FULL L AILERON INPUT. HE SAID THAT AS SOON AS HE PLACED THE 'B' SYS HYD SWITCH TO THE 'STANDBY RUDDER' POS THE RUDDER BECAME CONTROLLABLE AGAIN.