What was found
AUTO PILOT OUT OFF TRIM L/OFF ILLUMINATED APPROACHING TOC. ALL NECESSARY CHECK LIST PERFORMED. OBSERVED AUTO PILOT DISENGAGE USING CTL WHEEL PITCH TRIM, ALT TRIM AND MANUAL TRIM HANDLES COULD NOT MOVE STAB TRIM INDICATOR AT ALL. DUMPED FUEL TO GET BELOW MAX LANDING WEIGHT AND RETURNED BACK TO MIAMI. REMOVED AND REPLACED HORIZONTAL STABILIZER CHAIN DRIVE UNIT ASSY IAW MM 27-44-05. INSPECTED JACK SCREW & CHAIN HORIZONTAL STAB FOR ANY DEFECTS WERE NOTED AT THIS TIME; ALSO LUBED SYSTEM IAW MM 12-21-03; OPERATION CHECKED FOUND NORMAL IAW MM 27-44-00.