What was found
DESCENDING WITH AUTOPILOT ON, GOT A NOSE DOWN MIS-TRIM MESSAGE ON 802 PANEL. TOUCHED TCS BUTTON AND HAD A STRONG NOSE UPTRIM, ELEVATOR MANUAL TRIM WOULD NOT WORK UP OR DOWN (FROZEN). SHUT AUTOPILOT OFF WITH STANDBY TRIM, ACFT COULD NOT BE TRIMMED DOWN. MAINTENANCE TROUBLESHOT SYSTEM, FOUND A DATA PLATE FROM THE APU SUSPECT. IT HAD FALLEN INTO THE ELEVATOR ACTUATING CHAIN TRAY, POSSIBLY CAUSING JAM. DATA PLATE WAS REMOVED, AND RETAINED FOR RE-INSTALL. ACFT RETURNED TO SERVICE. ACFT TC: 17,966. (X)