Narrative:

Descending from 7000 ft to 5000 ft and 200 ft from 6000 ft when we were told to stop the descent at 6000 ft MSL, and we were slowing from 210 KIAS to 170 KIAS in trail of a B737 about 4 mi and also told to intercept the localizer. Simultaneous ILS approachs to runway 27R were in use. Numerous large aircraft in the area as well. We were given a turn to intercept runway 27L localizer while starting to level at 6000 ft, with autoplt engaged when we encountered a severe wake turbulence, rolling the aircraft hard right causing the autoplt to disengage. Captain took control of the airplane and required a left 90 degree roll input to level, followed by a severe wake to the left causing similar input to the right. It was all we could do to keep the aircraft level. This lasted about 15-20 seconds. Upon rollout, approach barked, 'I need a hard left turn now!' it took a moment to register that during this wake encounter, we continued on or near our heading through the ILS runway 27L localizer and into the path of the runway 27R approachs. Realizing what was going on, we turned left as instructed and were advised of traffic on the runway 27R approach and had visual contact on the airplane. We could not get a word in with ZAU. Finally, captain barked back at ATC regarding our inability to communicate with channel congestion. We told ATC what happened and their response was,' you are in trail a B737,' to which we replied that it did not matter what we were in trail of -- we were in a wake turbulence upset! We intercepted the runway 27L localizer and made an uneventful landing. Before handing us off to the tower controller, the approach controller did apologize. Upon landing, the flight attendants knew something had happened and numerous passenger deplaning asked us what the abrupt turning was all about.

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Original NASA ASRS Text

Title: AN MD80 APCHING ORD RWY 27L ILS 4 MI IN TRAIL OF A B737 ENCOUNTERED SEVERE WAKE TURB AND DEVIATED FROM ITS ASSIGNED APCH COURSE DURING THE RECOVERY.

Narrative: DSNDING FROM 7000 FT TO 5000 FT AND 200 FT FROM 6000 FT WHEN WE WERE TOLD TO STOP THE DSCNT AT 6000 FT MSL, AND WE WERE SLOWING FROM 210 KIAS TO 170 KIAS IN TRAIL OF A B737 ABOUT 4 MI AND ALSO TOLD TO INTERCEPT THE LOC. SIMULTANEOUS ILS APCHS TO RWY 27R WERE IN USE. NUMEROUS LARGE ACFT IN THE AREA AS WELL. WE WERE GIVEN A TURN TO INTERCEPT RWY 27L LOC WHILE STARTING TO LEVEL AT 6000 FT, WITH AUTOPLT ENGAGED WHEN WE ENCOUNTERED A SEVERE WAKE TURB, ROLLING THE ACFT HARD R CAUSING THE AUTOPLT TO DISENGAGE. CAPT TOOK CTL OF THE AIRPLANE AND REQUIRED A L 90 DEG ROLL INPUT TO LEVEL, FOLLOWED BY A SEVERE WAKE TO THE L CAUSING SIMILAR INPUT TO THE R. IT WAS ALL WE COULD DO TO KEEP THE ACFT LEVEL. THIS LASTED ABOUT 15-20 SECONDS. UPON ROLLOUT, APCH BARKED, 'I NEED A HARD L TURN NOW!' IT TOOK A MOMENT TO REGISTER THAT DURING THIS WAKE ENCOUNTER, WE CONTINUED ON OR NEAR OUR HDG THROUGH THE ILS RWY 27L LOC AND INTO THE PATH OF THE RWY 27R APCHS. REALIZING WHAT WAS GOING ON, WE TURNED L AS INSTRUCTED AND WERE ADVISED OF TFC ON THE RWY 27R APCH AND HAD VISUAL CONTACT ON THE AIRPLANE. WE COULD NOT GET A WORD IN WITH ZAU. FINALLY, CAPT BARKED BACK AT ATC REGARDING OUR INABILITY TO COMMUNICATE WITH CHANNEL CONGESTION. WE TOLD ATC WHAT HAPPENED AND THEIR RESPONSE WAS,' YOU ARE IN TRAIL A B737,' TO WHICH WE REPLIED THAT IT DID NOT MATTER WHAT WE WERE IN TRAIL OF -- WE WERE IN A WAKE TURB UPSET! WE INTERCEPTED THE RWY 27L LOC AND MADE AN UNEVENTFUL LNDG. BEFORE HANDING US OFF TO THE TWR CTLR, THE APCH CTLR DID APOLOGIZE. UPON LNDG, THE FLT ATTENDANTS KNEW SOMETHING HAD HAPPENED AND NUMEROUS PAX DEPLANING ASKED US WHAT THE ABRUPT TURNING WAS ALL ABOUT.

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.