DEHAVILLAND DHC8 FLC ADVISED APCH CTLR OUTSIDE THE OM THAT THEY WERE NOT LEGAL TO CONTINUE THE ILS APCH SINCE THE RPTED VISIBILITY WAS BELOW PUBLISHED MINIMUMS. THEY WERE VECTORED TO ANOTHER RWY ILS FOR THE APCH.

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WE WERE ON A FLT FROM DCA TO PHL. WHEN WE GOT WITHIN 40 MI OF ARPT; I GOT THE ATIS AT PHL. THE WINDS WERE LIGHT AND VARIABLE; VISIBILITY 1 3/4 MI; CEILING WAS 1500 FT BROKEN WITH A SCATTERED LAYER AT 300 FT. THE CTLR TOLD US TO EXPECT ILS RWY 9R. AS WE WERE BEING VECTORED; WE WERE SWITCHED TO ANOTHER CTLR WHO THEN TOLD US TO EXPECT THE CONVERGING ILS RWY 17. BY THIS TIME WE WERE ON DOWNWIND TO RWY 9R; APPROX 10 MI FROM THE LOC TO RWY 17. I TOLD THE PIC; WHO WAS PF; THAT THERE MUST BE A NEW ATIS (BECAUSE VISIBILITY MINIMUMS FOR CONVERGING ILS RWY 17 IS 2 MI). WE WERE VMC ON TOP OF LAYERS. THE VISIBILITY WAS AT LEAST 10 MI. BEFORE I COULD GET OFF TO SEE ABOUT NEW ATIS; THEY STARTED TO GIVE NEW VECTORS AND THEY CLRED US FOR THE APCH ABOUT 4 MI FROM OM. WE ACCEPTED THE APCH CLRNC AND WE WENT ANOTHER 2 MI BEFORE ANOTHER ACFT ASKED IF THE VISIBILITY HAD CHANGED AND THE CTLR SAID IT WAS 1 3/4 MI. WE IMMEDIATELY TOLD THE CTLR WE COULD NOT SHOOT THE APCH. AT THIS TIME WE WERE AT 2700 FT AND WERE STILL OUTSIDE THE OM. HE SOUNDED SURPRISED AND GAVE US A CLB TO 3000 FT AND VECTORS FOR ILS RWY 9L. I THINK THE CONTRIBUTING FACTORS FOR THIS WERE THE FACT THAT THE PIC AND I HAD WORKED 3 13-HR DAYS IN A ROW; MY LACK OF GETTING A NEW ATIS TO VERIFY MINIMUMS BEFORE ACCEPTING APCH CLRNC; THE HIGH WORKLOAD AT THE TIME CTLR SWITCHED RWYS; AND THE CTLR ASSIGNING US A NEW APCH FOR WHICH WE DID NOT HAVE MINIMUMS.