AN AVRO RJ85 (BA146) ENCOUNTERS WAKE TURB WHILE MAKING A PARALLEL APCH INTO MSP RWY 12R.

Narrative

FLYING INBOUND TO MSP; ATC CLRED THE FLT FOR THE ILS RWY 12R AND THE APCH MODE WAS SELECTED AND THE MISSED APCH ALT WAS SET FOR 5000 FT. AROUND 9-10 NM FROM THE RWY; THE TCASII DISPLAYED POP-UP TFC 2-3 MI DIRECTLY IN FRONT OF US (200 FT LOWER). I HAD POINTED THIS OUT TO THE FO AND WAS ABOUT TO QUESTION ATC; BUT THE ACFT HAD EXPERIENCED A LIGHT BUZZ TURB FOLLOWED BY A SHARP R ROLL. I DISCONNECTED THE AUTOPLT AND WAS ABLE TO RECOVER; BUT THIS WAS FOLLOWED BY A VERY STRONG L ROLL. THIS L ROLL COULD ONLY BE SLOWED WITH THE FULL R APPLICATION OF THE AILERONS. IT SEEMED LIKE THE ACFT WAS CAUGHT IN WAKE TURB AND IT MAY ROLL OVER. IN AN ATTEMPT TO STRENGTHEN LATERAL CTL; I CAUTIOUSLY ADDED R RUDDER TO PICK UP THE L WING; BUT THIS FAILED TO RETURN THE WINGS TO A LEVEL ATTITUDE. THE ONLY POSSIBLE ESCAPE FROM THIS WAKE TURB SEEMED TO BE THROUGH THE VERT PLANE. I SLAMMED THE THRUST LEVERS FORWARD AND CLBED. THIS WORKED AND NORMAL FLT CTL WAS REGAINED. I ANNOUNCED TO ATC A GAR FOR WAKE TURB; AND DEMANDED 5000 FT. AFTER ENGAGING THE AUTOPLT; I FOUND OUT THAT THE POP-UP TFC WAS A B747 ON AN APCH TO RWY 12L. I TOLD THE CTLR THAT WE HAD EXPERIENCED UNCOMMANDED ROLLS DUE TO WAKE TURB AND THAT THE WINDS AT 4000 FT WERE FROM NE AT 45 KTS. THE FLT WAS REVECTORED FOR ANOTHER APCH AND LANDED WITHOUT FURTHER INCIDENT. I THINK THIS WAKE TURB ORIGINATED FROM THE B747'S TAIL PLANE -- WHICH WOULD ASCEND ABOVE ITS ALT AND CAUSE A R ROLL FIRST; FOLLOWED BY THE L ROLL. IF MY ASSUMPTION IS CORRECT; THE STRENGTH FROM A B747'S WING VORTEX WOULD BE A VERY DANGEROUS MATTER. I WOULD LIKE TO RESTATE: THIS ACFT COULD ONLY IMPEDE THIS L ROLL AND A VERT ESCAPE WAS REQUIRED TO REGAIN CTL OF THE ACFT. IN THE LAST 11 YRS OF FLYING AT THIS AIRLINE; I HAD ENCOUNTERED MANY TYPES OF WAKE TURB FROM VARIOUS ACFT; BUT NONE OF THIS PWR. ATC IS BRINGING ACFT CLOSER AND CLOSER THESE DAYS; PLACING CREWS AT MORE RISK FOR WAKE TURB ENCOUNTERS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN THE WAKE TURB STRUCTURED CALLBACK PROGRAM. THE PRECEDING B747 DID NOT SHOW ON TCASII UNTIL SHORTLY BEFORE THE OCCURRENCE. WHEN IT DID SHOW; IT WAS ONLY 2-3 MI AWAY. RPTR ACFT WAS ABOUT 200 FT ABOVE THE B747 GLIDE PATH. RPTR THINKS THE WAKE WENT UPWARD AS A RESULT OF THE HORIZ STABILIZER FORCES OF THE B747. RPTR ACFT HAD 50 DEG ROLL TO THE R FOLLOWED BY A 60 DEG ROLL TO THE L. AILERON AND RUDDER WERE USED TO UPRIGHT THE ACFT. ONLY PARTIAL CTL WAS AVAILABLE. FLC EXECUTED A GAR AND PERFORMED ANOTHER ILS APCH. WHEN PARKED AT THE GATE; THE FO WAS STILL SHAKING. IT WAS A STRESSFUL INCIDENT.