As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PDX - ON FIIGHT 2359, ON APPROACH THE RUDDER TRIM QUIT WORKING. ON THE SECOND ATTEMPT RIGHT RUDDER TRIM MOVED THE TRIM RAPIDLY TO THE RIGHT. LEFT RUDDER TRIM MOVED THE TRIM FURTHER AND RAPIDLY TO THE RIGHT AS WELL. CIRCUIT BREAKER PULLED PER RUNAWAY CHECKLIST. MAINTENANCE REMOVED AND REPLACED RUDDER TRIM/AILERON TRIM CONTROL PANEL. RESET CIRCUIT BREAKER. OPERATIONAL CHECK GOOD. AIRCRAFT RETURNED TO SERVICE.