What was found
INVESTIGATED FLIGHT CREW REPORT OF REPEATED MACH TRIM AND ELEVATOR TRIM FAIL ANNUNCIATOR INDICATIONS DURING DESCENT. DURING TROUBLESHOOTING FOUND ELEVATOR TRIM WOULD STOP IN SAME POSITION EACH TIME DURING OPERATION. NOTED AUTOPILOT TRIM INPUTS WOULD STOP JUST BEFORE FAILURE. FOUND DUAL SYNCHRO TRANSDUCER FAILED INTERNALLY. REPLACED THE DUAL SYNCHRO TRANSDUCER WITH A SERVICEABLE UNIT, NO FAULTS NOTED DURING POST-INSTALLATION CHECKS. RECOMMEND MANUFACTURER CHECK FAILURE RATE ON THIS COMPONENT TO VERIFY AN ISOLATED CONDITION TO THIS UNIT OR A FLEET PROBLEM.