What was found
DURING DESCENT, HAD NR 3 ENGINE HP DUCT OVERHEAT WHEN USING AIRFOIL AND ENGINE ANTI-ICE. FOLLWED PROCEDURE PER PDM AND OVERHEAT REOCCURED. SHUTOFF BOTH ENGINE ISOLATION AND HIGH PRESSURE VALVE FOR NR 3 ENGINE, OVERHEAT WENT OUT THEN ENTIRE CABIN FILLED WITH SMOKE. LANDED SLC WITHOUT INCIDENT. TROUBLESHOOTING FOUND NR 3 AIR EJECTOR AIR TEMP SENSOR FAULTY. REPLACED SENSOR OPERATION NORMAL.