WAKE TURB ENCOUNTER.

Narrative

AT ORD ON R DOWNWIND FOR RWY 4R ABEAM MIDFIELD AUTOPLT ENGAGED. WHEN WE CHKED IN WITH OUR FINAL APCH CTLR HE ADVISED WE WERE FOLLOWING A MD11 CAUTION WAKE TURB. WE WERE CLRED TO DSND FROM 7000 FT TO 4000 FT. AS I STARTED DOWN IT BECAME OBVIOUS THAT WE WERE ENTERING THE WAKE OF THE MD11. THE RIDE WAS SIMILAR TO LIGHT TURB. JUST AS I BEGAN TO SHALLOW THE DSCNT IN ORDER TO REMAIN ABOVE THE WAKE OUR ACFT ROLLED AT A RAPID RATE TO THE L. I DISENGAGED THE AUTOPLT AT APPROX 30 DEGS OF BANK AND APPLIED FULL R AILERON TO STOP THE ROLL. THE ACFT WAS SLOW IN RESPONDING AND EXCEEDED 40 DEGS OF BANK BEFORE STARTING TO ROLL BACK TO LEVEL. THE CAPT REQUESTED GREATER SEPARATION FROM THE MD11 AND ATC RESPONDED BY GIVING US 5 MI IN TRAIL. THE REMAINDER OF THE FLT WAS UNEVENTFUL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN THE WAKE TURB STRUCTURED CALLBACK PROGRAM. DURING CALLBACK THE RPTR FELT THE BEGINNING OF THE WAKE ENCOUNTER DESCRIBING IT AS LIGHT TURB. THEN THE SHARP JOLT OCCURRED AND ROLLED THE ACFT INTO A 40 DEG BANK. THERE WAS NOT MUCH FLT PATH DISPLACEMENT BUT THE ROLL WAS ACCOMPANIED WITH AN INCREASE IN 'G' FORCES AND SOME YAW. THE ACFT WAS TAKEN OFF OF AUTOPLT AND MANUAL CTL FORCES WERE USED FOR THE RECOVERY. RPTR FELT THAT FULL CTL DEFLECTION COULD NOT STOP THE ROLL. THE AUTOPLT WAS LEFT ON AS THE BANK INCREASED TO 30 DEGS; THEN DISCONNECTED; MANUAL INPUT COULD NOT STOP THE ROLL FROM INCREASING TO 40 DEGS OF BANK. RPTR FELT THAT THE UNUSUAL ATTITUDE TRAINING OFFERED BY HIS ACR WAS MOST HELPFUL IN THE RECOVERY PROCESS. WHAT HE WOULD DO DIFFERENTLY DURING RECOVERY NEXT TIME; IS ADD MORE RUDDER INTO THE DIRECTION OF THE DESIRED ROLL. ENCOUNTER WAS A BIG SURPRISE TO ALL OF THE FLC. RPTR WOULD ASK CTLR FOR MORE SPACING THE NEXT TIME HE IS FOLLOWING A HVY JET.