Narrative:

Wake turbulence encounter. Location: prior to GS on runway 22R ILS approach. We were IMC on ILS final to runway 22R at ord at 5000 ft and cleared for the approach. We had been slowed down to 160 KTS and advised to use caution for wake turbulence as we were following a B757. Spacing was approximately 4.5 mi on our TCASII scope. The B757 ahead of us was flying 500 ft high according to our TCASII altitude indication. The first officer and I commented that we were going to hit his wake, and that we would be ready for it. I believe that the B757 was following another B757 and was probably flying high to avoid its wake. When we hit the wake, it exceeded the ability of our autoplt to control the aircraft. The autoplt disconnected and I hand flew as the aircraft rolled approximately 25 degrees left and right -- certainly enough to concern our passenger. I informed approach control that we were going to climb 200 ft and told him why. He said ok, but commented that the spacing was good. I responded that I was not complaining about the spacing but that we were being 'beat up' by the wake. I was prepared to fly 1/2 DOT high on the GS if necessary to avoid his wake, but once on the GS, the wake was not a problem. Upon landing, I called the approach facility on the hotline in ord to explain what had happened. The person I spoke to said he would pass it to the controller. The purpose of this report is not to criticize the controller, but to point out the affect of a B757 on an MD80 in that situation.

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Original NASA ASRS Text

Title: MD80 CREW ENCOUNTERED WAKE TURB BEHIND A B757-200 WHICH ALMOST EXCEEDED THE CTL CAPABILITY OF THE ACFT.

Narrative: WAKE TURB ENCOUNTER. LOCATION: PRIOR TO GS ON RWY 22R ILS APCH. WE WERE IMC ON ILS FINAL TO RWY 22R AT ORD AT 5000 FT AND CLRED FOR THE APCH. WE HAD BEEN SLOWED DOWN TO 160 KTS AND ADVISED TO USE CAUTION FOR WAKE TURB AS WE WERE FOLLOWING A B757. SPACING WAS APPROX 4.5 MI ON OUR TCASII SCOPE. THE B757 AHEAD OF US WAS FLYING 500 FT HIGH ACCORDING TO OUR TCASII ALT INDICATION. THE FO AND I COMMENTED THAT WE WERE GOING TO HIT HIS WAKE, AND THAT WE WOULD BE READY FOR IT. I BELIEVE THAT THE B757 WAS FOLLOWING ANOTHER B757 AND WAS PROBABLY FLYING HIGH TO AVOID ITS WAKE. WHEN WE HIT THE WAKE, IT EXCEEDED THE ABILITY OF OUR AUTOPLT TO CTL THE ACFT. THE AUTOPLT DISCONNECTED AND I HAND FLEW AS THE ACFT ROLLED APPROX 25 DEGS L AND R -- CERTAINLY ENOUGH TO CONCERN OUR PAX. I INFORMED APCH CTL THAT WE WERE GOING TO CLB 200 FT AND TOLD HIM WHY. HE SAID OK, BUT COMMENTED THAT THE SPACING WAS GOOD. I RESPONDED THAT I WAS NOT COMPLAINING ABOUT THE SPACING BUT THAT WE WERE BEING 'BEAT UP' BY THE WAKE. I WAS PREPARED TO FLY 1/2 DOT HIGH ON THE GS IF NECESSARY TO AVOID HIS WAKE, BUT ONCE ON THE GS, THE WAKE WAS NOT A PROB. UPON LNDG, I CALLED THE APCH FACILITY ON THE HOTLINE IN ORD TO EXPLAIN WHAT HAD HAPPENED. THE PERSON I SPOKE TO SAID HE WOULD PASS IT TO THE CTLR. THE PURPOSE OF THIS RPT IS NOT TO CRITICIZE THE CTLR, BUT TO POINT OUT THE AFFECT OF A B757 ON AN MD80 IN THAT SIT.

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.