Narrative:

We were on a 180 degree heading at 190 KTS, 8000 ft. All rates of descent were normal. Approach was from northwest our jvl VOR. We could see ord area traffic heavy to the east of airport. Now cleared down to 7000 ft, 180 degree heading and 190 KTS. Approximately 15 DME north of ord we were cleared to 5000 ft 'caution wake turbulence, in- trail with a B747' was advised by ord approach. I had the traffic at the 7 mi range on TCASII. At approximately 6000 ft we encountered strong wake turbulence and a 20 degree roll to the left. I was hand flying the aircraft and held the roll to 20 degrees. I stopped the descent and began to climb out of it when a pronounced roll right occurred. I held opposition to the roll and held it to a 45-50 degree right bank. I recovered and departed to the west, heading 220 degrees at 6300 ft. We advised ord of the encounter and deviation to the west. We were reclred for the runway 9R ILS. I could sense the B747 wake below us on the GS and I maintained 3/4 DOT high to accommodate a safe and smooth approach. All else normal. B747 landed ord on runway 9R and used all of the runway for landing. I believe he was high during ord arrival and approach. No conflict with other traffic. We knew the east was busy, the west was the best route to take. I know how busy ATC can get. Perhaps if an aircraft is known to be higher than usual, it can be advertised as 'in- trail with heavy XXX high.' callback conversation with reporter revealed the following information: reporter participated in the wake turbulence incident callback questionnaire. Reporter was amazed at the strength of the wake even though he was 15 mi behind. The first encounter wasn't too severe, but the second encounter moved his aircraft several hundred ft, had no aileron control and the aircraft was not responding the rudder input. It lasted for 7 seconds while the reporter found his elevator controls effective and slowly climbed out of the wake. Reporter has a good suggestion in having aircraft who are having problems following a wake producing aircraft, notify ATC that they will be flying slightly to upwind side of localizer.

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Original NASA ASRS Text

Title: WAKE TURB ENCOUNTER.

Narrative: WE WERE ON A 180 DEG HDG AT 190 KTS, 8000 FT. ALL RATES OF DSCNT WERE NORMAL. APCH WAS FROM NW OUR JVL VOR. WE COULD SEE ORD AREA TFC HVY TO THE E OF ARPT. NOW CLRED DOWN TO 7000 FT, 180 DEG HDG AND 190 KTS. APPROX 15 DME N OF ORD WE WERE CLRED TO 5000 FT 'CAUTION WAKE TURB, IN- TRAIL WITH A B747' WAS ADVISED BY ORD APCH. I HAD THE TFC AT THE 7 MI RANGE ON TCASII. AT APPROX 6000 FT WE ENCOUNTERED STRONG WAKE TURB AND A 20 DEG ROLL TO THE L. I WAS HAND FLYING THE ACFT AND HELD THE ROLL TO 20 DEGS. I STOPPED THE DSCNT AND BEGAN TO CLB OUT OF IT WHEN A PRONOUNCED ROLL R OCCURRED. I HELD OPPOSITION TO THE ROLL AND HELD IT TO A 45-50 DEG R BANK. I RECOVERED AND DEPARTED TO THE W, HDG 220 DEGS AT 6300 FT. WE ADVISED ORD OF THE ENCOUNTER AND DEV TO THE W. WE WERE RECLRED FOR THE RWY 9R ILS. I COULD SENSE THE B747 WAKE BELOW US ON THE GS AND I MAINTAINED 3/4 DOT HIGH TO ACCOMMODATE A SAFE AND SMOOTH APCH. ALL ELSE NORMAL. B747 LANDED ORD ON RWY 9R AND USED ALL OF THE RWY FOR LNDG. I BELIEVE HE WAS HIGH DURING ORD ARR AND APCH. NO CONFLICT WITH OTHER TFC. WE KNEW THE E WAS BUSY, THE W WAS THE BEST RTE TO TAKE. I KNOW HOW BUSY ATC CAN GET. PERHAPS IF AN ACFT IS KNOWN TO BE HIGHER THAN USUAL, IT CAN BE ADVERTISED AS 'IN- TRAIL WITH HVY XXX HIGH.' CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN THE WAKE TURB INCIDENT CALLBACK QUESTIONNAIRE. RPTR WAS AMAZED AT THE STRENGTH OF THE WAKE EVEN THOUGH HE WAS 15 MI BEHIND. THE FIRST ENCOUNTER WASN'T TOO SEVERE, BUT THE SECOND ENCOUNTER MOVED HIS ACFT SEVERAL HUNDRED FT, HAD NO AILERON CTL AND THE ACFT WAS NOT RESPONDING THE RUDDER INPUT. IT LASTED FOR 7 SECONDS WHILE THE RPTR FOUND HIS ELEVATOR CTLS EFFECTIVE AND SLOWLY CLBED OUT OF THE WAKE. RPTR HAS A GOOD SUGGESTION IN HAVING ACFT WHO ARE HAVING PROBS FOLLOWING A WAKE PRODUCING ACFT, NOTIFY ATC THAT THEY WILL BE FLYING SLIGHTLY TO UPWIND SIDE OF LOC.

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.