A CL65 ENCOUNTERS WAKE TURB BEHIND A B757 DURING APCH AT ORD.

Narrative

THE CTLR PUT US 2 1/2 - 3 MI BEHIND A B757 WITHOUT CAUTIONING US. WE ASKED HIS ACFT TYPE AND CTLR SAID 'ACR X B727.' THE ACR X REPLIED 'B757.' THEN OUR ACFT BEGAN AN UNCTLED L ROLL TO APPROX 45-60 DEGS. THE AUTOPLT DISENGAGED AND WE RECOVERED TO STRAIGHT AND LEVEL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN THE WAKE TURB CALLBACK STUDY. RPTR WAS CLOSE TO THE PRECEDING ACFT. HE THOUGHT IT WAS A B727 UNTIL THE PLT OF THE ACFT RPTED IT TO BE A B757. AT THAT TIME HE WAS ONLY 2 1/2 - 3 MI BEHIND. WHEN HE ENCOUNTERED THE WAKE HE DESCRIBED IT AS THE MOST FRIGHTENING EXPERIENCE HE HAS EVER HAD FLYING ANYTHING. THE BANK ROLL WENT TO 45 DEGS; DISENGAGING THE AUTOPLT. HE HAD PARTIAL CTL AND WAS ABLE TO RIGHT THE ACFT. A GAR WAS PERFORMED TO GET OUT OF THE WAKE. DURING FLC/ATC REVIEW; SUPVR STATED THE CTLR WOULD RECEIVE ADDITIONAL TRAINING. SUPPLEMENTAL INFO FROM ACN 427256: THE CAPT MADE VISUAL CONTACT WITH THE PRECEDING ACFT AND THIS PROMPTED HIM TO HAVE ME ASK APCH WHAT TYPE OF ACFT WE WERE FOLLOWING. THE APCH CTLR REPLIED; 'ACR X B727.' SHORTLY AFTER; A VOICE WITH A SPANISH ACCENT RESPONDED; 'B757.' WITHIN A FEW SECONDS; THE ACFT; WHICH WAS ON AUTOPLT AND COUPLED TO THE LOC; BEGAN AN UNCOMMANDED L BANK EXCEEDING 45-50 DEGS OF BANK. THE AUTOPLT DISENGAGED AND THE CAPT RECOVERED HDG 250 DEGS AND CLBING TO 5000 FT WHILE EXECUTING A GAR/MISSED APCH. THE CTLR NOTICED THIS AND CONFIRMED OUR GAR; ASSIGNING US A NEW HDG. I THEN QUESTIONED ATC TO VERIFY WHAT WE WERE FOLLOWING AND HE SAID 'B757.' WE THEN LANDED WITH NO FURTHER INCIDENT.