A CANADAIR CL 440 ON DSCNT AT 12000 FT DECLARED AN EMER DUE TO LOSS OF AIRFOIL ANTI-ICING WITH ANTI-ICE DUCT WARNING ILLUMINATED. CAUSED BY A FAILED SENSOR.

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I WAS THE CAPT ON FLT XXX FROM ERI TO ZZZ ON 1/THU/02 AT 12000 FT WE GOT A TRIPLE CHIME; MASTER WARNING AND AN ANTIICE DUCT MSG WHICH LED ME TO THE EMER PROCS CHKLIST IN OUR QRH. AFTER COMPLETING THE CHKLIST WE WERE LEFT WITH NO ICE PROTECTION ON OUR WINGS AND ENGINE COWLING. I THEN DECLARED AN EMER WITH APCH CTL; ADVISED HIM OF OUR SIT AND TOLD HIM WE CAN'T HAVE ANY DELAYS GETTING TO THE ILS APCH. I THEN CALLED OUR DISPATCH AND ASKED TO SPEAK TO OUR DISPATCHER AND MAINT. THEY HANDED ME TO MAINT CTL AND I ADVISED HIM OF OUR SIT; I DID NOT SPEAK TO OUR DISPATCHER BUT I ASSUMED MAINT WOULD HAVE FORWARDED THAT INFO TO HIM. BECAUSE OF OUR TIME CONSTRAINT I DID NOT HAVE TIME TO SPEAK TO OUR DISPATCHER AFTER MAINT. I THEN NOTIFIED OUR FA THAT I DECLARED AN EMER AND THAT WE PROBABLY WON'T NEED TO EVACUATE AND THAT IF WE NEEDED TO EVAC I WOULD COMMAND THAT ACTION. ALSO THAT THE CRASH/FIRE RESCUE VEHICLES WOULD BE FOLLOWING US DOWN THE RWY IN CASE THE PASSENGERS SEE THEM. AGAIN BECAUSE OF TIME I DID NOT PERSONALLY TELL THE PASSENGERS WE WERE AN EMER SIT. WE CONFIGURED FOR THE APCH PER OUR QRH EMER PROCS AND THE LNDG WAS UNEVENTFUL THE CRASH/FIRE VEHICLES WERE WAITING FOR US AS I REQUESTED FROM ATC. WE PULLED OFF THE RWY AND I ASKED THE FIRE CHIEF TO VISUALLY INSPECT OUR LEFT WING FOR SIGNS OF SMOKE OR ANYTHING ABNORMAL HE SAID EVERYTHING LOOKS OK. I THEN TOLD ATC WE CAN TAXI TO THE GATE. NO EVAC NECESSARY. PASSENGERS DEPLANED WITHOUT INCIDENT. I BELIEVE I FOLLOWED ALL PRECAUTIONS AND ACTED IN ACCORDANCE WITH COMPANY PROCS FOR THE EMER WITH THE WAY I HAVE BEEN TRAINED AND TOOK THE NECESSARY STEPS TO SEE TO IT THAT ATC WAS FULLY AWARE OF OUR SIT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE PROB WAS A FALSE WARNING ISOLATED TO THE LEFT WING LEADING EDGE ANTI-ICE DUCT SENSOR. THE RPTR SAID THIS WARNING WAS AT THE TIME THE ACFT WAS PICKING UP ICING AND THE FLT OPS MANUAL REQUIRES SWITCHING OFF THE AIRFOIL ANTI-ICING. THE RPTR STATED THE DUCT FAILURE PROB OCCURRED TO ANOTHER CREW ON THIS CANADAIR 440 BUT NOT IN ICING CONDITIONS.