What was found
(CAN) DURING CLIMB OUT WITH THE AUTOPILOT (AP) ENGAGED, THE PILOT DID A SMALL RUDDER TRIM INPUT AND IT WENT STEADILY OVER TO THE RT. THE AP WAS DISENGAGED AND CREW COULD IMMEDIATELY FEEL THE RUDDER IN A HARDOVER POSITION. BOTH PILOT AND COPILOT INPUTS WERE REQUIRED TO CONTROL THE RUDDER. AIR TRAFFIC CONTROLLER WAS ADVISED AND THE ACFT RETURNED/LANDED WITHOUT FURTHER INCIDENT. A MAINTENANCE TEAM TRAVELLED ON A AOG TRIP AND FOUND THE RUDDER TRIM SWITCH STUCK. THE AILERON/RUDDER TRIM PANEL WAS REPLACED, TESTED AND THE ACFT RELEASED FOR SERVICE.