NMAC.

Narrative

WE WERE CLRED TO DSND TO 3000 FT HDG 180 DEGS AND 180 KTS WHILE ON A 4-5 MI DOWNWIND FOR 36L IN TPA. APCH CTLR WAS EXTREMELY BUSY AND INVOLVED IN NON-STOP RADIO COMS. TCASII ALERTED US TO 'TFC' AT OUR 12 O'CLOCK POS AND 2 MI WITH LESS THAN 1000 FT VERT SEPARATION AS WE WERE LEAVING 3800 FT FOR 3000 FT. I WAS FLYING AND IMMEDIATELY REDUCED MY RATE OF DSCNT TO LESS THAN 500 FPM. AT THIS TIME THE FO ATTEMPTED TO ADVISE THE CTLR THAT WE WERE RESPONDING TO AN RA AS I STOPPED THE DSCNT AND BEGAN A CLB; PICKING UP THE ACFT VISUALLY. THE BONANZA WAS 200 FT BELOW US AND 300-400 FT BEHIND US; SLIGHTLY L; ON THE SAME HDG. TCASII WAS DIRECTING A 'CLB' AT 200-300 FPM. I BELIEVE THAT SOME XMISSIONS WERE BLOCKED ABOUT THIS TIME AS THE CTLR GAVE US A L TURN FOR THE BASE LEG AND THE BEECHCRAFT PASSED BEHIND US. HE LATER STATED THAT THE BONANZA WAS ASSIGNED 2500 FT AND THAT HE HAD CHANGED OUR ALT TO 3500 FT. WE NEVER RECEIVED THAT CLRNC. THE REMAINDER OF THE APCH AND LNDG WAS UNEVENTFUL. THE TWR SUPVR TOLD ME THAT HE HAD RELIEVED THE CTLR AND WAS GOING TO REVIEW THE TAPES. WE CONTINUE TO HAVE CLOSE CALLS IN THE TERMINAL AREA WITH TRANSITING VFR ACFT. CTLR WORKLOAD IS VERY HVY AND 'BLOCKED' XMISSIONS ARE COMMON. WE WERE NEVER ADVISED OF THE VFR TFC AND HAD IT NOT BEEN FOR THE TCASII THE INCIDENT COULD VERY EASILY HAVE BEEN AN ACCIDENT. ALLOWING VFR ACFT TO TRANSIT AN AIR CARRIER ARR CORRIDOR ON A BUSY DAY WITH ONLY 500 FT VERT SEPARATION IS A DISASTER WAITING TO HAPPEN.