A B737-800; ON VISUAL AT IAD; OVERSHOT TURN TO FINAL; RECEIVING A TCASII RA FROM TFC ON THE PARALLEL.

Narrative

ATC ASSIGNED AN AIRSPD OF 210 KIAS ON THE DOWNWIND LEG TO RWY 1L FOR A VISUAL APCH. ATC GAVE US A VECTOR TO BASE; INFORMED US OF TFC TO FOLLOW. WE RPTED THAT THE TFC WAS NOT IN SIGHT. JUST PRIOR TO XING THE EXTENDED CTRLINE; WE WERE CLRED FOR THE VISUAL APCH AND WE IMMEDIATELY BEGAN SLOWING FROM ASSIGNED SPD OF 210 KIAS. THE AUTOPLT WAS ENGAGED IN HDG MODE. BOTH THE CAPT AND MYSELF WERE LOOKING OUTSIDE FOR THE TFC AND FLEW THREW THE LOC. THE SIC MISTAKENLY TOOK TFC ON FINAL FOR THE PARALLEL TO BE THE TFC WE WERE TO FOLLOW. THE CAPT CALLED THE OVERSHOOT OF FINAL AND TURNED THE AIRPLANE TO A HDG TO CORRECT BACK TO FINAL FOR RWY 1L. DURING THE OVERSHOOT OF FINAL A TA THEN AN RA WAS RECEIVED FROM TFC ON RWY 1R. AFTER THE INCIDENT; WE INTERCEPTED FINAL TO RWY 1L AND A NORMAL APCH AND LNDG TOOK PLACE. CONTRIBUTING FACTORS: THE RWY WAS ON THE CAPT'S SIDE OF THE PLANE ON THE BASE LEG MAKING IT DIFFICULT FOR THE SIC TO VISUALLY SEE THE RWY. I WAS NEW TO THE AIRPLANE; GETTING IOE. NIGHT AT AN UNFAMILIAR ARPT. APCH ASSIGNING THE SPD OF 210 KIAS UNTIL JUST PRIOR TO LOC INTERCEPT. RADIO CONGESTION RESULTED IN US NOT BEING ABLE TO REQUEST A SLOWER SPD. PERFORMANCE WAS AFFECTED BY A NEW PLT TO THE ACFT. TO PREVENT THIS PROB FROM OCCURRING AGAIN: PLT ACTION -- THE LOC INTERCEPT SHOULD HAVE BEEN ARMED IMMEDIATELY AFTER APCH CLRNC WAS GIVEN. ATC ACTION -- WHEN ATC HAS ASSIGNED A SPECIFIC SPD AND THE ACFT IS ON A CLOSE IN BASE LEG VECTOR TO FINAL; ATC SHOULD ISSUE 'SPD YOUR DISCRETION' OR CLR THE ACFT FOR A 'VISUAL APCH' SOONER THAN JUST PRIOR TO LOC INTERCEPT; THUS RELIEVING PLTS FROM HIGHER THAN NORMAL AIRSPDS IN THE ATA.