As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WITH AUTOPILOT SELECTED TO THE CAPTAINS SIDE AND AUTOPILOT ENGAGED, AIRCRAFT STARTED A SHALLOW CLIMB AND THEN AN ABRUPT DESCENT ACCOMPANIED BY A TRIM FAIL WARNING. AFTER THE AUTOPILOT WAS DISCONNECTED NORMAL FLIGHT RESUMED. (FLT 5474) REPLACED ELEVATOR AUTOPILOT SERVO. P/N 622-5734-002 S/N ON-3622 S/N OFF-9595.