Narrative:

Flying inbound to msp, ATC cleared the flight for the ILS runway 12R and the approach mode was selected and the missed approach altitude was set for 5000 ft. Around 9-10 NM from the runway, the TCASII displayed pop-up traffic 2-3 mi directly in front of us (200 ft lower). I had pointed this out to the first officer and was about to question ATC, but the aircraft had experienced a light buzz turbulence followed by a sharp right roll. I disconnected the autoplt and was able to recover, but this was followed by a very strong left roll. This left roll could only be slowed with the full right application of the ailerons. It seemed like the aircraft was caught in wake turbulence and it may roll over. In an attempt to strengthen lateral control, I cautiously added right rudder to pick up the left wing, but this failed to return the wings to a level attitude. The only possible escape from this wake turbulence seemed to be through the vertical plane. I slammed the thrust levers forward and climbed. This worked and normal flight control was regained. I announced to ATC a go around for wake turbulence, and demanded 5000 ft. After engaging the autoplt, I found out that the pop-up traffic was a B747 on an approach to runway 12L. I told the controller that we had experienced uncommanded rolls due to wake turbulence and that the winds at 4000 ft were from northeast at 45 KTS. The flight was revectored for another approach and landed without further incident. I think this wake turbulence originated from the B747's tail plane -- which would ascend above its altitude and cause a right roll first, followed by the left 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 aircraft could only impede this left roll and a vertical escape was required to regain control of the aircraft. In the last 11 yrs of flying at this airline, I had encountered many types of wake turbulence from various aircraft, but none of this power. ATC is bringing aircraft closer and closer these days, placing crews at more risk for wake turbulence encounters. Callback conversation with reporter revealed the following information: reporter participated in the wake turbulence 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. Reporter aircraft was about 200 ft above the B747 glide path. Reporter thinks the wake went upward as a result of the horizontal stabilizer forces of the B747. Reporter aircraft had 50 degree roll to the right followed by a 60 degree roll to the left. Aileron and rudder were used to upright the aircraft. Only partial control was available. Flight crew executed a go around and performed another ILS approach. When parked at the gate, the first officer was still shaking. It was a stressful incident.

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Original NASA ASRS Text

Title: 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.

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.