WAKE ENCOUNTER -- ACR ON FINAL APCH HITS THE WAKE OF A PRECEDING B747 AND ROLLS TO 20-25 DEGS OF L BANK.

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PRIOR TO TURNING FINAL ORD RWY 9R; I WAS GIVEN A 'CAUTION WAKE TURB B747' BY THE APCH CTLR. I DO NOT RECALL THE CTLR ISSUING SPACING INFO. HOWEVER; I USED NORMAL WAKE TURB AVOIDANCE PROCS. ON FINAL; I ENCOUNTERED LIGHT SYMMETRICAL BUFFET FOLLOWED BY A ROLL. I KNEW IMMEDIATELY AND INSTINCTIVELY WHAT IT WAS AND RAISED THE ACFT PITCH TO GET ABOVE THE VORTEX. I WAS IMMEDIATELY OUT OF THE TURB AFTER THE PITCH CHANGE AND I REALIGNED THE ACFT TO THE RWY. THE ACFT WAS IN A SAFE POS TO LAND AND DID SO. THE LNDG AND ROLLOUT WAS NORMAL AND UNEVENTFUL. I PROCEEDED TO THE GATE DIRECTLY AND WAS UNABLE TO MAKE ANY ANNOUNCEMENTS. HOWEVER; I DID STAND AT THE DOOR AS I ALWAYS DO. I RECALL 1 PAX ASKING WHAT HAPPENED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR SAID THAT HE KNEW THAT THE PRECEDING ACFT WAS A B747 BECAUSE HE HAD SEEN THIS ACFT ON ITS FINAL APCH LEG WHILE HE WAS FLYING DOWNWIND IN HIS MD80; SUPER 80. HE STAYED 1 DOT HIGH ON THE GS AFTER HE TURNED FINAL UNTIL HE GOT CLOSE TO THE FINAL APCH FIX. AS THE RPTR NEARED THE GS; IN THE VICINITY OF THE FAF; HE FELT A LITTLE LIGHT TURB. AS HE INTERCEPTED THE GS THE MD80 ROLLED TO THE L TO A BANK ANGLE OF ABOUT 25 DEGS. THE PLT RECOVERED BY USING FULL R AILERON AND BY CLBING. HE WAS ABLE TO STOP THE ROLL AND START SLOWLY TO THE UPRIGHT; BUT THE REAL RECOVERY DID NOT BEGIN UNTIL HE HAD CLBED ABOVE THE WAKE. HE SAID THAT HE HAD READ AN ARTICLE FROM NASA ABOUT WAKE TURB AND FROM THIS HE KNEW THAT CLBING WAS THE BEST TECHNIQUE. THE CAPT SAID THAT SINCE THIS EVENT HE HAS HAD SEVERAL OTHER WAKE ENCOUNTERS. ONE; BEHIND A B757; WAS PARTICULARLY EXCITING WITH THE BANK ANGLE APCHING 90 DEGS.