ACR FLT CREW REPORTS NIDUQ FIX ON THE BTV ILS RWY 33 IS MISPLACED IN THE FMC DATABASE. FMC HAS IT AT 20 DME SHOULD BE AT 15 DME.

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WE REQUESTED DIRECT NIDUQ FROM ZBW AND GRANTED. BEGAN DSCNT FROM ALT AND HANDED OFF TO BURLINGTON APCH. CLRED DOWN TO 6000 FT MSL. UPON ARRIVING AT 6000 FT; BURLINGTON APCH TURNED US TO A 360 DEG HDG AND TOLD US '3 FROM NIDUQ MAINTAIN 5400 FT UNTIL NIDUQ AND CLRED FOR THE ILS DME 33 APCH.' MY FO NOTICED THAT NIDUQ ON OUR FMS NAV DISPLAY WAS BEHIND US AND QUERIED APCH CTL. APCH CTL SAID THAT ANOTHER ACFT (DIFFERENT OPERATOR) HAD THE SAME PROB AND THAT HE WOULD CALL OUT THE NIDUQ FIX FOR US. HE CALLED NIDUQ AT 15 DME I-VOE WHICH WAS THE CORRECT DISTANCE PER THE ILS DME 33 COMMERCIAL CHART APCH PLATE; BUT ON OUR ACFT FMS NAV DISPLAY NIDUQ WAS DISPLAYED ON THE 5 MI RING BEHIND US (AT 20 DME). WE DID NOT DSND UNTIL WE INTERCEPTED THE GS. THE GPWS DID NOT ACTIVATE. I TOLD THE TWR CTLR THAT THERE WAS A PROB WITH THE DATABASE POS OF NIDUQ AND THAT I WOULD FILE PAPERWORK. AFTER PARKING; I NOTIFIED THE COMPANY OF THE PROB. NIDUQ IS SUPPOSED TO BE ON TOP OF MOUNT MANSFIELD; ELEVATION 4088 FT. WITH FMS POS 5 MI FARTHER OUT ON THE LOC COURSE; THERE IS A CHANCE THAT A CREW COULD CROSS AN ERRONEOUS FIX AT 20 DME ON THE LOC COURSE AT 5400 FT AND THEN STEP DOWN THE NEXT FIX ALT (4800 FT AT 13 DME) LEAVING ONLY 712 FT OF TERRAIN SEPARATION WITH THE MOUNTAIN.