What was found
ON FLIGHT 4477 THE CREW REPORTED THE MAIN PITCH TRIM WAS INOPERABLE DURING CLIMBOUT. BACKUP PITCH TRIM WORKED FINE. THE CREW DECLARED AN EMERGENCY AND FOLLOWED AOM-1 PROCEDURES. THE CREW REQUESTED FOR CFR TO STANDBY FOR LANDING AS A PRECAUTIONARY MEASURE. THE AIRCRAFT LANDED WITHOUT INCIDENT. THE AIRCRAFT WAS REMOVED FROM SERVICE. FOUND HSCU FAIL ON CMC. REMOVED AND REPLACED THE CONTROL UNIT HORIZONTAL STAB IAW 27-40-01. CONTROL UNIT HORIZONTAL STAB PART NUMBER 362100-1013. PROBLEM DID NOT FIX. FOUND FIRST OFFICER’S YOKE PITCH SWITCH FAULTY. REMOVED AND REPLACED THE FIRST OFFICER’S F/O YOKE PITCH SWITCH IAW 27-40-03. HARNESS W7044 PART NUMBER 145-63000-401. THE OPERATIONAL CHECK WAS GOOD. THE AIRCRAFT WAS RETURNED TO SERVICE.