AN LTT ACR HAD AN ENCOUNTER WITH SEVERE WAKE TURB REQUIRING A GAR.

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WE HAD BEEN CLRED FOR AN ILS TO 27L IN ATL. WE JOINED THE FINAL AT 3500 FT AND; AS THE GS STARTED TO MOVE; WE GOT HIT BY WAKE TURB THAT BANKED THE ACFT ABOUT 45 DEGS TO THE R. WE RECOVERED AND CONTINUED. WE ASKED APCH FOR THE TYPE OF ACFT WE WERE FOLLOWING. HE STATED THAT WE WERE 3 1/2 MI BEHIND AN LGT. WE INTERCEPTED THE GS AND GOT HIT AGAIN BY WAKE TURB ALTHOUGH NOT AS BAD. WE HAD THE ARPT IN SIGHT AND DECIDED TO STAY ABOVE THE GS TO AVOID THE WAKE. WE WERE ABOUT 1 1/2 DOTS HIGH; ABOVE THE GS WHEN WE HIT EXTREME WAKE TURB; THE ACFT VIOLENTLY ROLLED INTO A 90 DEG BANK TO THE R; PITCHED 10 TO 12 DEGS DOWN; AND THE IAS WENT TO ZERO IN LESS THAN 5 SECONDS. IT TOOK BTWN 130-140 PERCENT TORQUE TO RECOVER AND START FLYING AGAIN. WE INITIATED A GAR AND ADVISED THE TWR. WE RETURNED FOR A NORMAL LNDG. AFTER LNDG; WE LEARNED FROM ANOTHER COMPANY PLT THAT; BEFORE WE SWITCHED TO THE TWR FREQ; THE LGT HAD RPTED TO THE TWR THAT HE WAS FULL DEFLECTION ABOVE THE GS BECAUSE OF WAKE TURB FROM A WDB. THE TWR CLRED THE LGT FOR A VISUAL APCH AFTER THE LGT SAID HE SAW THE ARPT. THE LGT MADE A QUICK DSCNT AND LANDED. BECAUSE OF THIS; OUR NORMAL PROC OF STAYING ABOVE THE GS TO STAY OUT OF HARM'S WAY DID NOT WORK. THE TWR SHOULD HAVE TOLD US THAT THE LGT WENT HIGH. I WOULD HAVE ABANDONED THE APCH. IN ATL; WE FOLLOW MANY DIFFERENT TYPES OF LARGE ACFT AND THE LGT HAS THE WORST WAKE TURB. I THINK THAT THE LGT SHOULD BE CLASSIFIED AS A HEAVY SO WE COULD GET HVY SEPARATION. 3 MI BEHIND AN LGT IS TOO CLOSE.