A CANADAIR CL-65 DURING A MAINT FERRY TO CORRECT RUDDER OSCILLATIONS WHEN ON A 6 MI FINAL APCH EXPERIENCED AN UNCOMMANDED YAW AND ROLL 40 DEGS TO THE LEFT THEN A BANK TO THE R 25 DEGS. LANDED WITHOUT FURTHER INCIDENT.

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WE WERE FLYING A SCHEDULED FLT FROM ZZZ TO ZZZ1 AND STARTED TO NOTICE A YAWING MOTION WITH THE AUTOPLT. WE WERE AT FL310 AT 0.74 MACH. I BROUGHT UP THE FLT CTL PAGE TO SEE IF THE RUDDER WAS OSCILLATING. IT WAS. I TURNED OFF THE AUTOPLT TO SEE IF THE YAWING CONTINUED. IT DID. I CALLED MAINT TO DISCUSS THE PROBLEMS SINCE THERE WAS NO APPROVED CHKLIST. IT TOOK A WHILE TO GET THE INFO WE NEEDED FROM THEM. BY THE TIME THAT WE CAME BACK INTO CONTACT WITH THEM WE WERE STARTING OUR DSCNT IN TO ZZZ1. WHEN ON THE GND IN ZZZ1 I CALLED MAINT. WE DISCUSSED THE PROB. THEY HAD ME GO TO THE ACFT AND POWER UP THE HYDRAULIC SYSTEMS AND ENGAGE THE YAW DAMPER AND SEE IF THE RUDDER OSCILLATIONS CONTINUED TO OCCUR. THEY DID NOT DUPLICATE. I TOLD MAINT THAT I AS WELL AS MY FO WERE COMFORTABLE FERRYING THE ACFT TO A MAINT BASE. WE GOT ALL OF THE REQUIRED PAPERWORK COMPLETED AND TOOK OFF TO ZZZ2 MAINT BASE. ONCE AGAIN WE EXPERIENCED THE SAME YAWING. WE EXPECTED THIS. THE FLT WAS NORMAL FOR THE CLB; CRUISE; AND DSCNT. ON APCH TO RWY AT ZZZ2 IN VMC CONDITIONS THE YAWING INCREASED. I WAS HAND FLYING THE ACFT. ABOUT 2500 MSL ON THE DSCNT TO THE RWY WE EXPERIENCED SOME LIGHT TURBULENCE. WITH THIS TURB WE EXPERIENCED AN UNCOMMANDED YAW AND ROLL TO THE L. WHEN I LOOKED DOWN I SAW THE BANK ON THE PRIMARY FLT DISPLAY AT OR ABOVE 40 DEG TO THE L. I COUNTERACTED THIS WITH RIGHT AILERON. WE THEN GOT A BANK TO THE RIGHT. THIS I COUNTERACTED WITH LEFT AILERON. I ESTIMATE THE BANK TO THE RIGHT AT ABOUT 20-25 DEG. THIS WAS THE ONLY UPSET WE EXPERIENCED. WHEN LOOKING AT THE INSTRUMENTS I SAW THE BRICK; LIKE A BALL GO FULL OUT TO THE LEFT 3/4 AND OUT TO THE R. WE LANDED WITHOUT FURTHER INCIDENT. I FILLED OUT THE REQUIRED COMPANY PAPERWORK AND TURNED IT IN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT DURING THE MAINT FERRY HE EXPERIENCED THE YAW OSCILLATIONS AS EXPECTED. THE RPTR SAID ON THE SIX MI FINAL APCH AT 2500 FT ON DSCNT HE ENCOUNTERED LIGHT TURB AND AN UNCOMMANDED YAW AND ROLL TO THE LEFT AT OR ABOVE 40 DEGS AND COUNTER ACTED WITH R AILERON. THE RPTR STATED HE THEN GOT A BANK TO THE R 25 DEGS AND USED L AILERON TO CORRECT AND THE AIRPLANE THEN FLEW OK TO A NORMAL LNDG. THE RPTR SAID THE MAINT ACTION WAS TO ADJUST THE RUDDER SECONDARY FEEL UNIT SPRING TENSION DUE TO BEING FOUND OUT OF LIMITS. THE RPTR SAID THE AIRPLANE WAS TEST FLOWN AND OSCILLATIONS WERE STILL PRESENT. THE RPTR STATED THE CORRECTIVE ACTION WAS REPLACEMENT OF THE LIGHTENING/HIGH INTENSITY RADIATED FIELD PROTECTION CIRCUIT CARD IN THE INTEGRATED AVIONICS PROCESSOR. THE RPTR SAID THIS CIRCUIT CARD WAS FOUND 'FRIED' AND REPLACED. THE RPTR SAID NO FURTHER RUDDER OSCILLATIONS WERE RPTED ON THE AIRPLANE WHEN BACK IN SVC.