What was found
ON APPROACH RECEIVED AMBER AP STAB TRIM & RETRIM NOSE DOWN CAS MESSAGES. CREW DISCONNECTED THE AUTOPILOT AND BEGAN TO NOTICE A HEAVINESS IN THE CONTROLS. THIS CONCERNED THEM AND PROMPTED THEM TO DECLARE AN EMERGENCY WITH ATC. CREW THEN ENGAGED THE SECONDARY TRIM SYSTEM AND THE CONTROLS RETURNED TO NORMAL CORRECTIVE ACTION; REPLACED HORIZONTAL STAB LINEAR ACTUATOR IN REF TO CESSNA MODEL 680A AMM 27-40-05. RIGGING AND OPERATIONAL CHECKS SATISFACTORY. ALL WORK DONE IN REF. TO CE-680A AMM 27-40-00.