Narrative:

We were being vectored to ord ILS runway 27L behind a B757. Although currently VMC, rain and mist had been a problem all day long. Chicago approach -- 128.45 -- gave us a final vector to join the localizer -- heading about 300 degrees, and at 5000 ft MSL. As I, the PNF, was responding to the clearance, the aircraft was suddenly and strongly rolled about 45 degrees angle of bank to the left, then 45 degrees angle of band right before we cleared the area of turbulence. The TCASII does not have a reliable scale for determining distance, but best guess is 5 NM or slightly closer.

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Original NASA ASRS Text

Title: E145 CREW HAD AN ENCOUNTER WITH SEVERE WAKE TURB FROM A PRECEDING B757-200 IN C-90 CLASS E.

Narrative: WE WERE BEING VECTORED TO ORD ILS RWY 27L BEHIND A B757. ALTHOUGH CURRENTLY VMC, RAIN AND MIST HAD BEEN A PROB ALL DAY LONG. CHICAGO APCH -- 128.45 -- GAVE US A FINAL VECTOR TO JOIN THE LOC -- HDG ABOUT 300 DEGS, AND AT 5000 FT MSL. AS I, THE PNF, WAS RESPONDING TO THE CLRNC, THE ACFT WAS SUDDENLY AND STRONGLY ROLLED ABOUT 45 DEGS ANGLE OF BANK TO THE L, THEN 45 DEGS ANGLE OF BAND R BEFORE WE CLRED THE AREA OF TURB. THE TCASII DOES NOT HAVE A RELIABLE SCALE FOR DETERMINING DISTANCE, BUT BEST GUESS IS 5 NM OR SLIGHTLY CLOSER.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.