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.