AN EQUIP MALFUNCTION AND A LOW ALTIMETER SETTING WITH AN ALT ASSIGNMENT AT THE LOWEST USABLE FLT LEVEL CONTRIBUTED TO A DHC8 FLC'S FAILURE TO LEVEL AT FL190. ALTDEV ALT OVERSHOT.

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WE WERE CLBING W OUT OF ALBANY; NY; AND HAD FILED FOR 16000 FT AS A FINAL. A DEEP SURFACE LOW WAS JUST PASSING NEW YORK STATE AT THE TIME WITH ALTIMETER SETTINGS OF 29.20 INCHES IN SYRACUSE AND 29.18 INCHES IN BUFFALO. 16000 FT PUT US NEAR THE TOPS OF THE CLOUDS WITH LIGHT TO MODERATE RIME ICING. A B737 JUST S OF OUR POS HAD RPTED SEVERE ICING AT 15000 FT SO WE ASKED FOR FL180 TO GET ABOVE THE CLOUDS. ZBW GAVE US 17000 FT FOR STARTERS; BUT WE WERE STILL IN THE TOPS; IN THE ICING. LEVEL AT 17000 FT I RAN THE DEICE BOOT CYCLE AND FOUND THAT THE R OUTER SEGMENT WOULD NOT INFLATE -- LEAVING THE 1/2 INCH OF ACCUMULATED ICE ON THAT SECTION. BOSTON THEN GAVE US 19000 FT FOR AN ALT. I SET 19000 FT IN THE ALT SELECT WINDOW OF THE AUTOMATIC FLT CTL SYS (AFCS AUTOPLT). THE TEMP WAS -30 DEGS C AND WE WERE FAIRLY LIGHT; SO THE CLB PERFORMANCE WAS STILL VERY GOOD AT 1200-1500 FPM. DURING THIS CLB I WAS ATTEMPTING TO GET THE OUTER R BOOT TO INFLATE MANUALLY; WHILE ALSO RECHKING THE OTHER SEGMENTS. PASSING FL180 FOR FL190; I CALLED '18 FOR 19; ALTIMETERS 29.92.' HOWEVER; BEING TIED UP WITH THE DEICE PANEL; I DID NOT IMMEDIATELY RESET THE ALTIMETER. WE WERE THROUGH FL183 WHEN I BEGAN TO SLOWLY RESET MY ALTIMETER; ALTHOUGH THE FO WAS THE PF THE AFCS WAS TIED TO MY INSTS (ONLY INSTS INTEGRATED WITH THE RNAV SYS). DUE TO THE EXTRAORDINARILY LOW ALTIMETER SETTING OF 29.18 INCHES; RESETTING TO 29.92 INCHES MADE NEARLY AN 800 FT INCREASE IN THE INDICATED ALT. WE ALSO CLBED SEVERAL HUNDRED FT DURING MY RESETTING; SO BY THE TIME I WAS NEARING 29.92 INCHES; I RECOGNIZED THAT WE WOULD PROBABLY INDICATE ABOVE FL190 BY THE TIME THE ALTIMETER WAS RESET. SO I INSTRUCTED THE FO TO LEVEL OFF AND START A SLOW DSCNT; REALIZING WE NEEDED TO ADJUST TO INDICATE FL190. (THE LEVELOFF PROBABLY TOOK 100 OR 200 FT ALSO; DUE TO THE RATE OF CLB.) INDEED; WE INDICATED FL194 BY THAT TIME; BUT ALREADY IN A SLOW DSCNT BY THE TIME MY ALTIMETER WAS FULLY SET. ZBW QUERIED US ON OUR ASSIGNED ALT. I RESPONDED FL190. HE SAID HE INDICATED 500 FT HIGH. I RESPONDED THAT WE WERE CORRECTING. I DID NOT EXPLAIN THE UNUSUAL CIRCUMSTANCES TO HIM. FLT LEVELS ABOVE FL180 ARE NOT A FREQUENT OCCURRENCE WITH US; PROBABLY ONLY 5 OR 6 TIMES IN THE LAST YR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THIS RPTR STATES THAT THE DH8 DEICE BOOT PROB WAS LIKELY JUST A RESULT OF A FROZEN PNEUMATIC LINE FOR THAT BOOT SEGMENT (THERE ARE ABOUT 5 SEGMENTS PER WING); AND THAT HE JUST DIDN'T THINK ABOUT THE SIGNIFICANCE OF THE LOW ALTIMETER UNTIL AFTER THE FACT.