TCASII RA PREVENTS A POTENTIAL CONFLICT FROM GETTING TO BE ANY MORE THAN THAT.

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THE FLT WAS BEING CTLED BY CRW APCH. APCH REQUESTED A REDUCTION TO FINAL APCH SPD AND A DSCNT TO 3000 FT. A FEW SECONDS LATER; THEY (APCH) GAVE A TURN TO 250 DEGS AND SAID TO RESUME NORMAL SPD. THE ACFT HAD SLATS WITH 15 DEGS FLAPS IN ORDER TO CONFIGURE FOR THE APCH AND REDUCE THE AIRSPD PER ATC'S REQUEST. THE ACFT WAS DSNDING AT 2000 FPM (AT 5500 MSL) WHEN TCASII GAVE A TA AND RAPIDLY CHANGED TO AN RA. TCASII CALLED 'CLB; CLB' AND THE VSI SHOWED GREEN COMMAND LIGHTS REQUIRING A CLB OF 1500 FPM OR GREATER. DUE TO THE CONFIGN OF THE ACFT (I.E.; SLATS AND FLAPS 15 DEGS; 2000 FPM DSCNT; AND UNSPOOLED ENGS); THE ACFT CONTINUED TO DSND TO 4500 FT MSL. IT TOOK MAX PWR AND THE CAPT'S ASSISTANCE TO THE FO IN ORDER TO ARREST THE DSCNT AND BEGIN CLBING. ATC SAID THAT WE TURNED INTO THE VFR ACFT; EVEN THOUGH THEY GAVE A TURN FROM 210 DEGS TO 250 DEGS. THERE WAS NO MENTION (FROM ATC) ABOUT THE VFR ACFT UNTIL AFTER THE EVASIVE ACTION WAS PERFORMED. BOTH PLTS HAD 250 DEGS ON THEIR HDG BUGS AND 3000 FT. THE CLB COMMAND WAS CANCELLED AT ABOUT 5000 FT. ATC GAVE A L TURN TO 190 DEGS AT WHICH TIME THE ARPT WAS SIGHTED AND A VISUAL APCH CLRNC WAS ISSUED. SUPPLEMENTAL INFO FROM ACN 221506: MY LAST SCAN OF THE TCASII UNIT SHOWED 0 FT VERT SEPARATION AT 4500 FT. ATC MADE CALLS; HOWEVER; WE WERE UNABLE TO RESPOND AS WE HAD NO FREE HANDS. ONCE IN THE CLR; I ADVISED ATC WHAT HAPPENED. HE SAID HE WAS 'AWARE OF TFC' BUT HE POINTED TFC OUT TO US. HE ALSO SAID 'WE TURNED INTO TFC;' ALL THE WHILE WE WERE ON A 250 DEG ASSIGNED HDG. VISUAL CONTACT WITH INTRUDING ACFT WAS NEVER MADE. A BRIEF PAX ANNOUNCEMENT WAS MADE TO ALLEVIATE ANY CONCERNS DUE TO THE ABRUPTNESS OF THE MANEUVERS. DURING DEPLANING MOST PAX APPEARED RELIEVED AND THANKFUL THAT ACR UTILIZES TCASII EQUIP. THIS CAPT IS ALSO THANKFUL.