Narrative:

Positioned 6 mi behind B747-400. Wind, direct crosswind at 5 KTS. Based on reported wind, elected to fly the visual approach 1 DOT high on the GS. Briefed this and a touchdown beyond B747 touchdown. Got good visual on B747 tire smoke and had aim point approximately 1500 ft down the 1200 ft runway. At 200 ft AGL, encountered violent roll, which required almost full aileron to control, followed immediately by equally violent roll in opposite direction. Elected to discontinue landing. Executed missed approach and returned for normal landing. Separation and extra care won't always avoid the turbulence. Callback conversation with reporter revealed the following information: the captain stated that there may have been a quartering tailwind. That, he thought, might have raised the wake turbulence up into the aircraft's approach path instead of simply dissipating. He has followed B747-400's before and always exercised due caution. This incident was more of a random event, perhaps due to the surface wind. Supplemental information from acn 416859: tower reports 5 mi in trail of B747 after we asked when being handed off from approach. TCASII shows 6+ mi in trail as B747 is landing. Wind was 290 degrees at 4 KTS. At about 150 ft, aircraft rolled about 20 degrees one direction, then opposite. Suspect upwind vortex drifted into landing area.

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Original NASA ASRS Text

Title: A DC9-10 ON SHORT FINAL HAS TO EXECUTE A GAR WHEN ENCOUNTERING WAKE TURB FROM THE PRECEDING LNDG B747 ON RWY 21R AT DTW.

Narrative: POSITIONED 6 MI BEHIND B747-400. WIND, DIRECT XWIND AT 5 KTS. BASED ON RPTED WIND, ELECTED TO FLY THE VISUAL APCH 1 DOT HIGH ON THE GS. BRIEFED THIS AND A TOUCHDOWN BEYOND B747 TOUCHDOWN. GOT GOOD VISUAL ON B747 TIRE SMOKE AND HAD AIM POINT APPROX 1500 FT DOWN THE 1200 FT RWY. AT 200 FT AGL, ENCOUNTERED VIOLENT ROLL, WHICH REQUIRED ALMOST FULL AILERON TO CTL, FOLLOWED IMMEDIATELY BY EQUALLY VIOLENT ROLL IN OPPOSITE DIRECTION. ELECTED TO DISCONTINUE LNDG. EXECUTED MISSED APCH AND RETURNED FOR NORMAL LNDG. SEPARATION AND EXTRA CARE WON'T ALWAYS AVOID THE TURB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CAPT STATED THAT THERE MAY HAVE BEEN A QUARTERING TAILWIND. THAT, HE THOUGHT, MIGHT HAVE RAISED THE WAKE TURB UP INTO THE ACFT'S APCH PATH INSTEAD OF SIMPLY DISSIPATING. HE HAS FOLLOWED B747-400'S BEFORE AND ALWAYS EXERCISED DUE CAUTION. THIS INCIDENT WAS MORE OF A RANDOM EVENT, PERHAPS DUE TO THE SURFACE WIND. SUPPLEMENTAL INFO FROM ACN 416859: TWR RPTS 5 MI IN TRAIL OF B747 AFTER WE ASKED WHEN BEING HANDED OFF FROM APCH. TCASII SHOWS 6+ MI IN TRAIL AS B747 IS LNDG. WIND WAS 290 DEGS AT 4 KTS. AT ABOUT 150 FT, ACFT ROLLED ABOUT 20 DEGS ONE DIRECTION, THEN OPPOSITE. SUSPECT UPWIND VORTEX DRIFTED INTO LNDG AREA.

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.