ACR EXPERIENCES LESS THAN REQUIRED WAKE TURB SEPARATION BEHIND A B757.

Narrative

WE WERE GIVEN RADAR VECTORS FROM THE MACEY ARR TO THE APCH FOR RWY 26R ATL. SINCE TFC WAS HVY WE WERE ENTERED INTO A DOWNWIND AT 160 KIAS. IT APPEARED THAT WE INSERTED INTO FINAL AROUND FREAL AND AHEAD OF ANOTHER PLANE ON DOWNWIND/BASE. WE WERE AT 5000 FT MSL DURING THIS TIME. WE WERE TOLD TO INTERCEPT THE RWY 26R LOC. WE NOTICED ANOTHER PLANE (Y) JOINING FINAL AHEAD OF US IN A DSNDING INTERCEPT TO THE LOC RWY 26R. WE QUERIED APCH ABOUT CLRNC FOR A VISUAL SINCE WE WERE ABOUT TO INTERCEPT GS. WE SAID WE HAD THE FIELD AND APCH CLRED US TO DO THE VISUAL RWY 26R MAINTAIN 160 KIAS TO AJAAY. OUR SEPARATION FROM THE ACFT (Y) AHEAD WAS NEVER ANY MORE THAN 3 NM AS IT APPEARED ON TCASII AND VISUALLY. A COUPLE OF MI OUT OF AJAAY I SLOWED TO 155 KTS TO MAINTAIN 3 NM SEPARATION. AT AJAAY WE CONTACTED TWR AND THEY SAID WE WERE CLRED TO LAND #2 BEHIND A B757 (Y). WE WERE SURPRISED SINCE THAT WAS THE FIRST MENTION OF THAT ACFT TYPE AND OUR INITIAL SEPARATION OF 3 NM. I CONFIGURED AND SLOWED TO APCH AND LANDED ABOUT 10-15 SECONDS AFTER THE B757 (Y) CLRED. THE APCH AND LNDG WERE UNEVENTFUL BUT I WAS PRIMED FOR AN IMMEDIATE GAR THROUGHOUT. IF I HAD KNOWN THE ACFT TYPE EARLY IN THE APCH I WOULD HAVE REQUESTED AN IMMEDIATE SLOWDOWN TO AFFORD MORE SEPARATION. APCH DID NOT PROVIDE PROPER IN-TRAIL SEPARATION.