Narrative:

At about XX35 ut we were handed off from chicago center to ord approach, on V84, about 35 DME obk VOR 270 degree heading. We checked on frequency at 8000' with the ATIS. We were then told to maintain 7000' and intercept the runway 22R localizer. We were advised by approach that we would be flown through the localizer for spacing behind a heavy widebody transport and to descend and maintain 5000'. At this time I had the F/a prepare for landing. We had the widebody transport in sight at our 9:30 position and at about 8000'. We were given a turn to 180 degrees and intercept the localizer, maintain 5000', cleared for the approach, caution wake turbulence, 170 KIAS speed till ridge (OM), tower 126.90 at ridge. We acknowledged and the first officer called ready for landing. We intercepted the localizer and G/south at nolen intersection. About 30 seconds later we felt a few light bumps. Knowing that we were following a heavy, we increased to 1 DOT above the G/south in an effort to avoid any further turbulence. Approximately 5 seconds later we entered the wake of the hve and it rolled the aircraft to 60 degree bank left before the captain could recover to wings level. The occurrence lasted about 5 seconds. Approximately 10 seconds later we again entered the turbulence. Even though we had further increased our G/south deviation to 1 1/2 dots up. This was a more violent encounter, rolling the aircraft to 110 degree bank left. Full scale deflection of the controls (aileron and rudder) to the right was applied until the roll stopped, and then the captain rolled to wings level. No significant loss of altitude or heading occurred. He recovered slightly above G/south and on the localizer, the occurrence lasted approximately 8 seconds. Aircraft stabilized, we decided to continue to landing and to fly 2 dots high for the remainder of the approach. The fact that the widebody transport was above G/south till inside nolen intersection and used a high rate of descent to get down to G/south intercept was the major cause. It was inevitable that we would cross through his wake turbulence. Had we maintained G/south from the time we intercepted, we would have only delayed the fact that we were in a position of certain encounter; it would have only occurred at a lower altitude. Suggestions: had the widebody transport been on the G/south at nolen intersection we would have never had the encounter. The controller seemed to use standard vectors and altitudes. All turns and dscnts were anticipated. They should be made aware, however, that we rely on the fact that the aircraft we are following is on the G/south VFR and IFR alike. Our knowledge of the fact that wake turbulence sinks at 400 FPM is useless if the preceding aircraft is above our flight path. Not only must we use caution for wake turbulence, but the controller needs to plan by allowing the aircraft following the heavy to get above his approach path. Spacing is not the only answer, planning is. Flight altitudes and spacing, we need a chance.

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Original NASA ASRS Text

Title: AN LTT VECTORED BY TRACON APCH CTLR TO INTERCEPT ILS FINAL APCH COURSE BEHIND A WDB ENCOUNTERED WAKE TURBULENCE AND ACFT ROLLED 60 DEGREES LEFT. A FEW SECONDS LATER ACFT ENCOUNTERED WAKE TURBULENCE AGAIN, BUT MORE SEVERE.

Narrative: AT ABOUT XX35 UT WE WERE HANDED OFF FROM CHICAGO CENTER TO ORD APCH, ON V84, ABOUT 35 DME OBK VOR 270 DEG HDG. WE CHKED ON FREQ AT 8000' WITH THE ATIS. WE WERE THEN TOLD TO MAINTAIN 7000' AND INTERCEPT THE RWY 22R LOC. WE WERE ADVISED BY APCH THAT WE WOULD BE FLOWN THROUGH THE LOC FOR SPACING BEHIND A HVY WDB AND TO DSND AND MAINTAIN 5000'. AT THIS TIME I HAD THE F/A PREPARE FOR LNDG. WE HAD THE WDB IN SIGHT AT OUR 9:30 POS AND AT ABOUT 8000'. WE WERE GIVEN A TURN TO 180 DEGS AND INTERCEPT THE LOC, MAINTAIN 5000', CLRED FOR THE APCH, CAUTION WAKE TURB, 170 KIAS SPD TILL RIDGE (OM), TWR 126.90 AT RIDGE. WE ACKNOWLEDGED AND THE F/O CALLED READY FOR LNDG. WE INTERCEPTED THE LOC AND G/S AT NOLEN INTXN. ABOUT 30 SECS LATER WE FELT A FEW LIGHT BUMPS. KNOWING THAT WE WERE FOLLOWING A HVY, WE INCREASED TO 1 DOT ABOVE THE G/S IN AN EFFORT TO AVOID ANY FURTHER TURB. APPROX 5 SECS LATER WE ENTERED THE WAKE OF THE HVE AND IT ROLLED THE ACFT TO 60 DEG BANK LEFT BEFORE THE CAPT COULD RECOVER TO WINGS LEVEL. THE OCCURRENCE LASTED ABOUT 5 SECS. APPROX 10 SECS LATER WE AGAIN ENTERED THE TURB. EVEN THOUGH WE HAD FURTHER INCREASED OUR G/S DEVIATION TO 1 1/2 DOTS UP. THIS WAS A MORE VIOLENT ENCOUNTER, ROLLING THE ACFT TO 110 DEG BANK LEFT. FULL SCALE DEFLECTION OF THE CONTROLS (AILERON AND RUDDER) TO THE RIGHT WAS APPLIED UNTIL THE ROLL STOPPED, AND THEN THE CAPT ROLLED TO WINGS LEVEL. NO SIGNIFICANT LOSS OF ALT OR HDG OCCURRED. HE RECOVERED SLIGHTLY ABOVE G/S AND ON THE LOC, THE OCCURRENCE LASTED APPROX 8 SECS. ACFT STABILIZED, WE DECIDED TO CONTINUE TO LNDG AND TO FLY 2 DOTS HIGH FOR THE REMAINDER OF THE APCH. THE FACT THAT THE WDB WAS ABOVE G/S TILL INSIDE NOLEN INTXN AND USED A HIGH RATE OF DSNT TO GET DOWN TO G/S INTERCEPT WAS THE MAJOR CAUSE. IT WAS INEVITABLE THAT WE WOULD CROSS THROUGH HIS WAKE TURB. HAD WE MAINTAINED G/S FROM THE TIME WE INTERCEPTED, WE WOULD HAVE ONLY DELAYED THE FACT THAT WE WERE IN A POS OF CERTAIN ENCOUNTER; IT WOULD HAVE ONLY OCCURRED AT A LOWER ALT. SUGGESTIONS: HAD THE WDB BEEN ON THE G/S AT NOLEN INTXN WE WOULD HAVE NEVER HAD THE ENCOUNTER. THE CTLR SEEMED TO USE STANDARD VECTORS AND ALTS. ALL TURNS AND DSCNTS WERE ANTICIPATED. THEY SHOULD BE MADE AWARE, HOWEVER, THAT WE RELY ON THE FACT THAT THE ACFT WE ARE FOLLOWING IS ON THE G/S VFR AND IFR ALIKE. OUR KNOWLEDGE OF THE FACT THAT WAKE TURB SINKS AT 400 FPM IS USELESS IF THE PRECEDING ACFT IS ABOVE OUR FLT PATH. NOT ONLY MUST WE USE CAUTION FOR WAKE TURB, BUT THE CTLR NEEDS TO PLAN BY ALLOWING THE ACFT FOLLOWING THE HVY TO GET ABOVE HIS APCH PATH. SPACING IS NOT THE ONLY ANSWER, PLANNING IS. FLT ALTS AND SPACING, WE NEED A CHANCE.

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.