What was found
RECEIVED A 'PITCH MISTRIM' MESSAGE ON ADU IN FLIGHT ATL-TRI. PILOT DISCONNECTED THE AUTOPILOT AND ATTEMPTED TO TRIM MANUALLY AS WELL AS USING THE STANDBY SYSTEM. NO TRIM LESS THAN 1/4 NOSE DOWN TRIM WAS AVAILABLE. AIRCRAFT RETURNED TO ATL WHERE LANDING WAS MADE SAFELY AND WITHOUT FURTHER INCIDENT. REMOVED AND REPLACED THE LEFT ELEVATOR TRIM TAB ACTUATOR IAW MM. OPERATIONAL CHECKS WERE GOOD ON GROUND RUN AND AIRCRAFT WAS RELEASED FOR FURTHER SERVICE. (M)