LJ45 OVERTAKING A DHC8 RPTS THE ACFT IN SIGHT AND IS INSTRUCTED BY A ZTL CTLR TO MAINTAIN VISUAL SEPARATION WHILE DSNDING TO A LOWER ALT.

Narrative

SIT DEVELOPED AS MY ACFT WAS ASKED TO IDENT A DASH 8 10-12 MI S OF OUR POS. MYSELF (PF) AND THE PNF BOTH EASILY IDENTED THE ACFT'S POS AND STROBE LIGHTS. AT THIS TIME; THIS CTLR TOLD US THE DASH 8 WAS LEVEL 1000 FT BELOW US (AT 16000 FT) AND CLRED US TO 'MAINTAIN VISUAL SEPARATION WITH THAT TFC; DSND AND MAINTAIN 11000 FT.' I INITIATED A 2000 FPM RATE OF DSCNT IN VERT SPD MODE ON THE AUTOPLT. APPROX 20 SECONDS INTO THE MANEUVER; A CREW MEMBER ON THE DASH 8 NOTIFIED ATC 'HE WAS GETTING AN RA;' BUT DID NOT SAY HE WAS FOLLOWING IT. THE CTLR RESPONDED THAT WE HAD THE DASH 8 IN SIGHT; AND WE WERE VISUALLY DSNDING THROUGH HIS ALT. THOUGH I RECEIVED A CLB RA AT THIS TIME; I WAS WELL BELOW THE DASH 8'S ASSIGNED ALT OF 16000 FT AND BELIEVED AN INCREASED RATE OF DSCNT WOULD BE THE BEST THING TO DO. OUT OF ABOUT 14000 FT; IT BECAME APPARENT THE DASH 8 WAS RAPIDLY DSNDING ON A COLLISION COURSE WITH US. I DISCONNECTED THE AUTOPLT INITIATED A 45 DEG BANK TO THE L AS THE DASH 8 PASSED BY 3 O'CLOCK HIGH -- WE WILL NOT BE ACCEPTING NIGHT-TIME VISUAL SEPARATION CLRNCS IN THE FUTURE.