AN ACR MD83 ON RADAR VECTORS TO THE FINAL APCH COURSE IS UNABLE TO COMMUNICATE WITH THE CTLR DUE TO FREQ CONGESTION AND CROSSES FINAL. A TCASII RA IS RECEIVED ON A DH8 MAKING A STRAIGHT-IN VISUAL APCH RESULTING IN A 200 FT CLB. AFTER XING FINAL APCH COURSE; THE MD83 RECEIVED APCH CLRNC.

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WE WERE ON A L DOWNWIND ON DSCNT FOR SEATAC WHEN THE PROB BEGAN. THE APCH CTLR ON FREQ 119.5 HANDED US TO FINAL APCH ON 133.65. IT WAS A BEAUTIFUL; CLR EVENING; AND WE HAD SEATAC MALL AND THE ARPT INSIGHT AND ANTICIPATED THE MALL VISUAL APCH TO RWY 34L/R (THE APCH IN PROGRESS). FROM THE FIRST CALL ON 133.65; THE CTLR WAS TOTALLY COVERED UP -- NONSTOP CHATTER. WE NORMALLY FLY FURTHER S TO COMMENCEMENT BAY BEFORE BEING TURNED IN OR CLRED FOR THE MALL VISUAL. THE CTLR TURNED US TO A 070 DEG HDG DOWN TO 3000 FT MSL JUST PRIOR TO THE MALL; TO FIT US IN HIS TFC FLOW. WE WERE SLOWED TO APPROX 190 KIAS TO MAKE THE 90 DEG TURN TO FINAL AT APPROX 7 DME FROM THE ARPT. THE CTLR WAS SO BUSY THAT HE FAILED TO ISSUE CLRNC FOR THE MALL VISUAL OR ANYTHING ELSE. THE FREQ WAS SO CONGESTED THAT I (FO WAS FLYING) COULD NOT CALL TO PROMPT HIM. A COMMUTER DASH 8 (ACR Y) HAD BEEN CLRED FOR THE MALL VISUAL TO RWY 34R WHEN 15 DME S OF SEATAC. WE SHOULD HAVE BEEN CLRED FOR VISUAL RWY 34L. THE AT OR ABOVE ALT OVER THE MALL IS 3000 FT -- EXACTLY WHERE ACR Y (90 DEGS TO US COMING FROM THE S) AND US WERE CLOSE TO MEETING. OVER THE MALL; WE GOT A TCASII RA WHICH COMMANDED A CLB WHICH WE FOLLOWED. ACR Y HAD US IN SIGHT. I WAS FINALLY ABLE TO ASK APCH FOR A CLRNC. WE WERE GIVEN RWY 34R AND ACR Y RWY 34L. WE HAD ALREADY OVERSHOT RWY 34R AND CLBED APPROX 200 FT; BUT THE FO DID AN EXCELLENT JOB GETTING THE ACFT IN THE SLOT AND STABILIZED FOR LNDG. THE SHORT TURN-IN ON BASE LEG WAS UNUSUAL; BUT WOULD HAVE WORKED IF WE HAD BEEN CLRED THE MALL VISUAL WHEN GIVEN THAT 070 DEG HDG. CAUSES: CTLR WORKLOAD; FREQ CONGESTION; NON ROUTINE SHORT TURN-IN TAKING HIM OUT OF HIS NORMAL TIMING AND PACING.