As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON FLIGHT 3955 THE CREW REPORTED THE PITCH TRIM MAIN INOPERABLE. REPORTED THE BACKUP TRIM WORKED IF AUTO PILOT LEFT ON. GOT AP MIS TRIM ALL LANDING PARAMETERS NORMAL. THE CREW DECLARED AN EMERGENCY AND RETURNED TO ORD. THE AIRCRAFT LANDED WITHOUT INCIDENT. THE AIRCRAFT WAS REMOVED FROM SERVICE. REMOVED AND REPLACED HORIZONTAL STABILIZER ACTUATOR IAW 140 AMM 27-40-01. THE OPERATIONAL CHECK WAS GOOD. THE AIRCRAFT WAS RETURNED TO SERVICE.