SAAB 340 FLT CREW HAS DEICING EQUIP MALFUNCTION.

Narrative

ON DSCNT INTO SAW WE BEGAN TO ACCRETE CLR ICE. DUE TO THIN CLOUD DECK AND GND TEMPS; '1 CYCLE' WAS SELECTED ON THE DEICE BOOTS. I WATCHED THE OUTBOARD DEICE BOOT INFLATE AND NOTICED THAT ONLY THE INNER HALF OF THE BOOT INFLATED. I POINTED THIS OUT AND WE RESELECTED THE 1-CYCLE DEICE AGAIN. I AGAIN NOTICED THAT ICE WAS NOT BEING BROKEN OFF THE OUTER MOST SECTION OF THE DEICE BOOT. HP VALVES WERE ON FOR ALL DEICE ATTEMPTS. THE INNER BOOT ON THE OUTER SECTION OPERATED NORMALLY. FO NOTED THAT THE BOOTS ON HER SIDE WERE TOTALLY NORMAL. WE RECEIVED NO COCKPIT INDICATION THAT OUR BOOTS WERE NOT WORKING PROPERLY. SEVERAL ATTEMPTS WERE MADE ONCE ON THE GND TO SEE IF WE STILL HAD THE SAME PROB. AGAIN ONLY HALF OF THE OUTER BOOT INFLATED. MAINT WAS CONTACTED ONCE WE UNLOADED ALL THE PAX AT THE GATE. WHAT WAS MOST ALARMING; WAS THAT WE HAD AN UNPROTECTED AIRFOIL SURFACE WITH NO INDICATION TO US. WE FELT LUCKY THAT WE WERE ABLE TO SEE THE SURFACE VISUALLY. HAD IT BEEN ANY OTHER SURFACE; WE NEVER WOULD HAVE NOTICED IT UNTIL WE HAD TOO MUCH ICE AND HAD A CONTROLLABILITY ISSUE.