IN TRAIL SEPARATION CRITERION NOT MET BEHIND A B-757. TEMPORARY LOSS OF ACFT CTL.

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ACR B737-100 ARR AT DTW. SUNNY AFTERNOON; 6 MI VISIBILITY IN HAZE. SIMULTANEOUS ILS APCHS TO RWY 21L AND 21R. VECTORED FOR EXTENDED DOWNWIND DUE TO OTHER ARR TFC. TURNED FINAL RWY 21L ABOUT 20 MI OUT. REQUESTED BY APCH TO SLOW FROM 210 KTS TO 190 KTS. 2 PARALLEL ACFT SHOWED UP ON TCASII 3 1/2 MI AHEAD ON FINAL. APCH REQUESTED US TO SLOW TO 170 KTS. FO FLYING; SLOWED. APCH CLRED US FOR ILS; ASKED US TO MAINTAIN 150 KTS TO OM AND TURNED US OVER TO TWR. OTHER ACFT ON FREQ AHEAD OF US HAD BEEN GIVEN SIMILAR SPDS AND CLRNCS. OP APPEARED NORMAL; TIGHT SPACING FOR ARR TFC. HAZE PREVENTED SEEING OTHER ACFT. TCASII GAVE US A HEADS UP ON HOW TIGHT THEY WERE SPACING US. 'WE WERE IN THE HANDS OF THE CTLR.' WE WERE SPACED 3 1/2 MI BEHIND TFC ON FINAL FOR ABOUT 10 MI. WE STARTED DOWN ILS RWY 21L GS; PUT THE FLAPS TO 15 DEGS WITH FINAL SLOW DOWN AND PULLED THROTTLES TO IDLE. ENCOUNTERED HVY WAKE TURB UNCTLABLE ROLL; 30 DEG BANK L; ACCOMPANIED WITH BRIEF STALL SHAKER WARNING; STAYED IN WAKE TURB. WE ASKED TWR 'WHAT KIND OF ACFT IN FRONT OF US' TWR'S ANSWER; 'B757.' WE SAID 'THANKS FOR THE WARNING; WE JUST GOT TWISTED IN HIS WAKE.' HE TURNED US OUT ON A GAR. WE SAID WE'D GIVE HIM A CALL ON THE TELEPHONE. I TALKED TO THE ATC APCH AREA SUPVR AND TOLD HIM WHAT HAPPENED AND THAT IF WE HAD BEEN JUST 'INFORMED' WE WERE BEHIND A B757 WE COULD HAVE CONFIGURED EARLIER; KEPT OUR ENGS SPOOLED UP AND FLOWN HIGH ON THE GS AND STAYED OUT OF HIS WAKE. FIX: ATC SUGGESTION HAVE ALL B757 COMPUTER CODED ON THE RADAR SCOPE WITH AN 'H' JUST LIKE THE HVY'S SO CTLRS WILL AUTOMATICALLY PROVIDE SEPARATION. HE SAID 4 MI IS REQUIRED BEHIND B757'S. MAKE IT MANDATORY FOR CTLRS TO INFORM ACFT FOLLOWING B757'S. PLTS SHOULD ALWAYS ASK WHAT KIND OF ACFT THEY ARE FOLLOWING WHEN THEY ARE NOT TOLD AND THE SPACING IS TIGHT.