CARJ FLT CREW ON APCH TO IAD IS UNCERTAIN AS TO WHICH RWY THEY HAVE BEEN CLRED TO LAND. CONGESTED APCH FREQUENCY DELAYS CORRECTION UNTIL LATE IN APCH.

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UPON DSCNT TO IAD WE WERE TOLD TO EXPECT RWY 19L. WE WERE TOLD BY POTOMAC APCH TO LOOK FOR TFC AT 10 O'CLOCK POS. WE WERE JUST TO THE NW OF IAD ON THE BARIN ARR. WE WERE TOLD TO FOLLOW TFC AND WERE CLRED FOR THE VISUAL. AS WE TURNED TOWARD THE FIELD WE NOTICED THE ACFT IN FRONT OF US WAS LNDG RWY 19R. WE MADE 3 ATTEMPTS TO CONTACT APCH TO CLARIFY THAT WE WERE CLRED FOR THE VISUAL RWY 19L. ALL 3 ATTEMPTS WERE BLOCKED OUT BY OTHER ACFT. I KEPT MY TURN TO THE FIELD SHALLOW AS WE WERE IN LIMBO. WE SWITCHED TO TWR FREQ WHERE WE WERE TOLD THAT WE LOOKED L OF COURSE AND THAT WE WERE CLRED TO LAND RWY 19R. WE WERE L OF COURSE BECAUSE OF THE SHALLOW TURN (NOT SURE OF WHICH RWY WE WERE LNDG ON). WE LINED UP WITH RWY 19R AND LANDED. NOTHING ELSE WAS MENTIONED. WE WERE NEVER TOLD BY POTOMAC TO EXPECT A CHANGE IN RWYS. BEING BLOCKED OUT 3 TIMES ON APCH FREQ MADE IT WORSE. THE ONLY TIME WE COULD HAVE BEEN TOLD ABOUT RWY 19R WAS WHEN APCH TOLD US TO FOLLOW TFC AND CLRED US FOR THE VISUAL. APCH MAY HAVE MENTIONED RWY 19R AT THAT TIME. IF HE DID; THEN BOTH OF US MISSED IT AND THE ONLY EXCUSE I HAVE IS THAT WE WERE SO ENGROSSED IN LOOKING FOR OUR TFC THAT WE MISSED THE RWY ASSIGNMENT. AGAIN; THAT IS THE ONLY TIME WE WOULD HAVE BEEN TOLD ABOUT RWY 19R. IF THAT WAS THE CASE THEN WE NEED TO DO A BETTER JOB MULTI-TASKING.