EMB145 FLT CREW LWOC AT IAD.

Narrative

THE EVENT OCCURRED DURING THE APCH AND LNDG TO RWY 19R AT IAD. THE POTOMAC APCH CTLR TURNED US TO A BASE LEG ON THE ILS TO RWY 19R AT APPROX 3000 FT. FLYING A HDG OF 090 DEGS; WE FLEW THROUGH THE LOC. BEFORE I COULD QUERY ATC; HE TURNED US BACK TO A HDG OF 240 DEGS AND WAS TOLD TO INTERCEPT THE LOC. AT NO POINT DID THE CTLR TELL US THAT WE WOULD BE FLYING THROUGH THE LOC. THE NEW INTERCEPT ANGLE WAS APPROX 50 DEGS AND WAS HAVING US ABOUT 8 MI FROM THE RWY. AT THIS POINT AT 3000 FT; WE WERE GIVEN THE CLRNC TO 'MAINTAIN 3000 FT UNTIL ESTABLISHED; CLRED FOR THE ILS RWY 19R.' MY FO DID A NICE JOB OF GETTING ON THE LOC AND ESTABLISHING OURSELVES INBOUND AFTER THE VERY POOR VECTORING. HAVING BEEN LEFT AT 3000 FT WITH ALL THE VECTORING AND NOW ONLY ABOUT 2 MI FROM FEMKO (THE OM); WE HAD TO HURRY DOWN TO REACH THE GS WHICH WAS SHOWING ALMOST A FULL DEFLECTION DOWN. UPON XING THE FAF; WE WERE GEAR DOWN; FLAPS 22 DEGS; AND FINALLY ON A STABILIZED APCH UPON XING FEMKO. THERE WAS NO OTHER COM BTWN US AND THE POTOMAC APCH CTLR AFTER HE CLRED US FOR THE APCH. THE WX WAS VERY MARGINAL WITH THE ATIS RPTING 1 1/4 SM; OVCST AT 005 DEGS AND RAIN. WE BROKE OUT OF THE CLOUDS AT DECISION HT AND MADE A SAFE LNDG ON RWY 19R. EXITING THE RWY ON THE HIGH SPD TXWY IS WHEN I REALIZED THAT WE WERE STILL ON THE APCH CTL FREQ. I FLIPPED UP THE TWR FREQ AND THE TWR CTLR TOLD US TO TAXI TO THE GATE. WE TAXIED AND THE FLT ENDED WITHOUT FURTHER INCIDENT OR ANY OTHER QUERY FROM ATC.