As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE AIRCRAFT WAS BEING TAXIED BACK FROM GATE BY A MECHANIC, NOTICED A RUNAWAY RUDDER TRIM REPORTED TO HAVE BEEN OBSERVED TWICE BY THE MECHANIC. THE ROTARY SWITCH WAS DETERMINED TO BE THE CAUSE AND WAS REPLACED. THIS AIRCRAFT WILL BE RETURNED TO SERVICE AFTER ALL SCHEDULED MAINTENANCE IS COMPLETED. REPLACED RUDDER TRIM SWITCH IAW Q400AMM 27-22-11. OPS CHECK OK.