LEVEL ENRTE DHC8 MAKES EVASIVE TCASII MANEUVER FROM DSNDING LJ45 AS ZTL APPLIES VISUAL SEPARATION CRITERION.

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OUR ACFT WAS AT 17000 FT MSL. CTR CTLR ASKED US IF WE HAD OUR TFC IN SIGHT; APPROX 2 O'CLOCK POS LOW. I VISUALLY ACQUIRED TFC AND INFORMED CTLR. PF ASKED ME IF I HAD THE TFC. I POINTED TO THE OTHER ACFT AND REPLIED YES. WE NEEDED LOWER FOR XING RESTR ON THE BROOK 2 ARR. CTLR ASKED IF WE COULD MAINTAIN VISUAL SEPARATION FROM OTHER TFC. I REPLIED YES. CTLR TOLD OTHER ACFT 'LEAR HAS YOU IN SIGHT; WILL BE DSNDING THROUGH YOUR ALT.' HE THEN CLRED US TO DSND TO 15000 FT AND MAINTAINED VISIBILITY SEPARATION WITH THE DASH 8 AT 16000 FT. THE DASH 8 CREW REPLIED THAT THEY DID NOT HAVE US. WE BEGAN A STEEP DSCNT TO QUICKLY PASS THROUGH THE DASH 8'S ALT. THE SPACING LOOKED GOOD. ALL SEEMED NORMAL; THE DASH 8 CREW TOLD THE CTLR THEY WERE GETTING AN RA AND ASKED WHERE IS THE TFC? THE CTLR RESPONDED THAT YES THE LEAR IS DSNDING WITH YOU IN SIGHT. AT THIS POINT; WE GOT A CLB RA; BUT WE WERE DSNDING RAPIDLY TO GET BELOW THE DASH 8. I SAW 2500 FPM ON THE VSI. THIS IS WHEN THE DASH 8 CREW SAID THEY WERE GETTING A DSND RA AND WERE FOLLOWING IT; THEY COULD NOT SEE THEIR TFC. THE CTLR SAID A THIRD TIME -- 'THE LEAR HAS YOU IN SIGHT AND IS DSNDING THROUGH YOUR ALT.' WE BEGAN A L TURN AWAY FROM THE DASH 8. I BELIEVE THEY THEN SAW US; AS THEY BEGAN A DIVERGENT L TURN. I WAS PUZZLED AS TO WHY HE (DASH 8) CONTINUED (APPARENTLY) TO DSND TOWARDS US. IT JUST SEEMED THE WRONG THING TO DO. I HAVE SINCE LEARNED THAT AT SOME/ALL (?) AIRLINES; THE COMPANY RULE IS ALWAYS FOLLOW RA'S NO MATTER WHAT. IN THE VAST MAJORITY OF CASES; THAT IS PROBABLY THE CORRECT THING. IN THIS INSTANCE; WITH 3 CTLR CONFIRMATION OF OUR DSCNT CLRNC; SITUATIONAL AWARENESS WAS SACRIFICED FOR COMPANY POLICY. I BELIEVE THAT HAD WE CHANGED OUR ACTIONS; IE; FOLLOWED THE RA INTO A CLB; WE MAY HAVE BEEN PUTTING BOTH ACFT IN MORE DANGER OF A MIDAIR. WE ARE CURRENTLY CONSIDERING CAREFULLY IF THIS INCIDENT WILL FORCE US TO REFUSE SUCH CLRNCS IN THE FUTURE; ACCEPT THEM DAY ONLY; OR WHAT CHANGES WILL COME TO OUR COMPANY'S POLICIES AS A RESULT OF THIS.