DURING A GAR BECAUSE OF TFC DEPARTING ON A XING RWY; A BA4100 CREW HAD A NEAR MISS WITH A DORNIER ACR ON THE W SIDE OF THE ARPT. AT LEAST ONE OPERROR OCCURRED.

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WHILE ON 1/2 MI FINAL FOR RWY 21 AT DCA; THE TWR CTLR CLRED AN ACFT TO DEPART RWY 18. THE SIT WAS TOO TIGHT SO WE MADE A GAR. WE FLEW RWY HDG TO 1600 FT MSL. THE TWR CTLR CLRED US TO MAKE R TFC FOR RWY 15 AT DCA. WE ENTERED A R DOWNWIND FOR RWY 15. AS WE BEGAN OUR TURN FOR R BASE; WE GOT A TCASII RA TO CLB. I SAW ANOTHER ACFT AT MY 1 O'CLOCK POS AND SLIGHTLY LOWER THAN OUR ALT. I TOOK THE ACFT CTLS FROM THE FO AND RESPONDED TO THE TCASII RA WITH A L CLBING TURN TO AVOID THE CONVERGING TFC. A L TURN WAS THE BEST COURSE OF ACTION AS THE OTHER ACFT PASSED OFF TO OUR R. SUPPLEMENTAL INFO FROM ACN 421166: CLRED VISUAL APCH TO RWY 21 DCA. CHKED IN WITH DCA TWR; CLRED TO LAND RWY 21 DCA. ON 1/2 MI FINAL (OVER WEST POTOMAC PARK) ACR Z MD80 CLRED FOR TKOF RWY 18. I DETERMINED A LNDG ON RWY 21 AT DCA WOULD RESULT IN A COLLISION BTWN THE ROLLING ACR Z MD80 AND OUR ACFT AT THE INTXN OF RWYS 21 AND 18. A GAR WAS EXECUTED ON RWY HDG AT APPROX 1/4 MI FROM THE END OF RWY 21. CAPT REQUESTED A VECTOR HDG FROM THE DCA TWR. TWR'S RESPONSE: ENTER R TFC FOR RWY 15. CLBING R TURN TO 1600 FT WAS MADE. MY (FO) ATTN WAS PRIMARILY DIRECTED AT PROPER ALIGNMENT WITH THE RWY COMPLEX TO ALIGN ACFT FOR LNDG ON RWY 15 AND KEEPING THE ACFT AT A LEVEL ALT AND PROPER AIRSPD. TWR CALLED JET TFC ON FINAL TO RWY 18 SBOUND OVER THE POTOMAC RIVER. WE MADE VISUAL CONTACT WITH THE TFC. SHORTLY THEREAFTER AN RA WAS GIVEN BY THE TCASII FOR TFC IMMEDIATELY TO THE L AND BELOW OUR ACFT. I DID NOT HAVE VISUAL CONTACT WITH THE RA ACFT. CAPT SIGHTED THE RA ACFT AND TOOK CTL MAKING A 45 DEG BANKED CLBING L TURN TO CLR THE AREA. TWR SUPVR (NOT ORIGINAL TWR CTLR) BROKE IN AND TOLD US TO MAKE AN IMMEDIATE L TURN TO 270 DEGS. TWR'S CALL WAS MADE AFTER EVASIVE ACTION WAS INITIATED BY THE CAPT. RA ACFT WAS ACR Y DORNIER ON A VISUAL APCH TO RWY 15 AT DCA. THIS ACFT HAD NOT YET SWITCHED TO THE TWR FREQ. POSTFLT TELEPHONE CONVERSATION WITH THE TWR CTLR CONFIRMED THAT THE DORNIER TFC WAS NOT CALLED TO OUR ATTN PRIOR TO THE RA. AFTER TFC CONFLICT WAS RESOLVED; TWR INSTRUCTED A TURN BACK TO THE ARPT TO LAND RWY 15. ACR A JET TFC ON FINAL TO RWY 18 CALLED BY TWR. VISUAL CONTACT MADE; NO FACTOR. UNEVENTFUL APCH AND LNDG MADE ON RWY 15 DCA. POSTFLT TELEPHONE CONVERSATION WITH TWR SUPVR. SUPVR CLRLY STATED FAULT WAS ON THE TWR CTLR AND OUR ACTIONS WERE AS DIRECTED AND WERE NOT BEING CALLED INTO QUESTION BY THE TWR.