A SOCATA TBM700 RUDDER TRIM RAN AWAY CAUSING SEVERE FLT CONTROL PROBLEMS. THE PILOT HAD HEADING AND ALT DEVIATIONS.

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THE CTR CTLR INSTRUCTED ME TO DSND TO 10000 FT. AT THIS TIME WE WERE 80 NM FROM ZZZ VOR; I PROCEEDED TO DSND BUT AT APPROX XA30Z; 40 NM FROM ZZZ VOR I ADJUSTED THE RUDDER TRIM. THE TRIM SWITCH RESPONDED NORMAL AND RETURNED TO ITS NEUTRAL POS BUT THE RUDDER TRIM MOTOR CONTINUED RUNNING; THIS CAUSED THE LOSS OF THE ASSIGNED HDG. THE DEV WAS SEVERE TOWARDS THE R (S). I DISCONNECTED THE AUTOPLT AND USING PEDALS AND L AILERON; AND I REDUCED PWR AT THE SAME TIME. I NOTIFIED THE CTLR ABOUT THE PROB AND ASKED FOR TIME TO TRY TO SOLVE THE PROB AND TO TAKE CORRECTIVE ACTIONS. I DISCONNECTED THE BREAKERS RELATIVE TO THE AUTOPLT AND TRIMS; WHILE AT THE SAME TIME TRYING TO CTL AND FLY THE PLANE TO RETURN TO THE CORRECT ASSIGNED HDG. AT THE MOMENT THAT MY ALT WAS 8900 FT THE CTLR ASKED ME IF I WANTED TO DECLARE AN EMER. I TOLD HIM THAT NOT AT THAT TIME; THAT I WAS TRYING TO REGAIN CTL OF THE RUDDER TRIM RESETTING THE CIRCUIT BREAKERS. THE CTLR INDICATED THAT I NEEDED TO GET BACK TO 9200 FT AND I HAD THE OPTION TO LAND IN ZZZ OR ZZZ1. I INDICATED THAT I WANTED TO LAND AT RWY XX IN ZZZ BECAUSE OF ITS SIZE AND EMER EQUIP IN CASE IT WAS NEEDED. I COULD NOT GET BACK TO THE INDICATED ALT. I WAS ONLY ABLE TO CLB BACK TO 9100 FT; BECAUSE IT WAS VERY DIFFICULT TO CTL THE PLANE AND TRY TO RESOLVE THE PROB WITH THE RUDDER TRIM. THE CTLR INDICATED THAT I SHOULD DECLARE AN EMER; AND THAT IS WHAT I DID. 2 MINS AFTER DECLARING THE EMER AND AT APPROX 20 NM W OF ZZZ ARPT I WAS ABLE TO GET THE TRIM SWITCH UNSTUCK AND GET FULL CTL OF THE RUDDER. I ADVISED THE CTLR THAT I HAD SOLVED THE PROB AND CANCELED THE EMER. THE CTLR VERIFIED THAT I WAS CANCELING THE EMER AND TOLD ME TO CONTACT ZZZ APCH. THE CTLR AT ZZZ GAVE ME A CLR TO VISUAL APCH RWY XX; AND I LANDED WITHOUT ANY PROBS.