Narrative:

On approach 20 mi out we were told to slow, that we would be following a heavy. We complied, were descended and were told to capture the localizer, then cleared for the approach. We were 6 mi in trail of a heavy. WX conditions at the time were a broken ceiling at 800 ft, 6 mi. We were switched to tower and then cleared to land. We could see the preceding traffic at all times, and the runway intermittently. At about 1500 ft, we saw the heavy in front of us start a go around. We hit his wake at about 1200 ft AGL as we were entering the cloud tops. We later found out that it was a B747-400 and it rolled the aircraft 20 degrees in either direction as we passed through its wake. Tower never said a word about the preceding traffic making a miss. After we landed, I called tower, talked to a supervisor who told me that the B747 was unable to maintain the spacing required on the B757 in front of it, and was instructed by ATC to go around. When I asked why we weren't told of the go around, the supervisor said that the controllers were 'too busy' with the spacing issue to issue any further advisories. I would bet that any controller that has sat in a cockpit of an aircraft that has been hit with B747-400 wake turbulence would understand the importance of these advisories. The aim devotes 7 pages to wake turbulence. Nowhere in there does it reference this situation. If there is any situation guaranteed to establish a wake turbulence encounter, this would be it, and maybe some guidelines could be established, or thought given to some. The new 'heavy' transports have particularly nasty wake, and I don't see that improving any time soon. Callback conversation with reporter revealed the following information: reporter states that he feels ATC was remiss in not advising him of the go around of the B747. He could have at least been aware of the change of flight path and adjusted his own approach accordingly. At least he might have been prepared for the resulting wake activity. Reporter has reviewed the aim and there is no requirement to advise the trailing aircraft in such a situation. He feels there should be such a requirement. Reporter also feels the newer boeing wings develop much greater wake than previous ones.

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Original NASA ASRS Text

Title: FLC OF MD87 ENCOUNTERS WAKE FROM B747-400 ON APCH WHEN THE B747 IS INSTRUCTED TO MAKE A GAR BY TWR FOR SPACING.

Narrative: ON APCH 20 MI OUT WE WERE TOLD TO SLOW, THAT WE WOULD BE FOLLOWING A HVY. WE COMPLIED, WERE DSNDED AND WERE TOLD TO CAPTURE THE LOC, THEN CLRED FOR THE APCH. WE WERE 6 MI IN TRAIL OF A HVY. WX CONDITIONS AT THE TIME WERE A BROKEN CEILING AT 800 FT, 6 MI. WE WERE SWITCHED TO TWR AND THEN CLRED TO LAND. WE COULD SEE THE PRECEDING TFC AT ALL TIMES, AND THE RWY INTERMITTENTLY. AT ABOUT 1500 FT, WE SAW THE HVY IN FRONT OF US START A GAR. WE HIT HIS WAKE AT ABOUT 1200 FT AGL AS WE WERE ENTERING THE CLOUD TOPS. WE LATER FOUND OUT THAT IT WAS A B747-400 AND IT ROLLED THE ACFT 20 DEGS IN EITHER DIRECTION AS WE PASSED THROUGH ITS WAKE. TWR NEVER SAID A WORD ABOUT THE PRECEDING TFC MAKING A MISS. AFTER WE LANDED, I CALLED TWR, TALKED TO A SUPVR WHO TOLD ME THAT THE B747 WAS UNABLE TO MAINTAIN THE SPACING REQUIRED ON THE B757 IN FRONT OF IT, AND WAS INSTRUCTED BY ATC TO GAR. WHEN I ASKED WHY WE WEREN'T TOLD OF THE GAR, THE SUPVR SAID THAT THE CTLRS WERE 'TOO BUSY' WITH THE SPACING ISSUE TO ISSUE ANY FURTHER ADVISORIES. I WOULD BET THAT ANY CTLR THAT HAS SAT IN A COCKPIT OF AN ACFT THAT HAS BEEN HIT WITH B747-400 WAKE TURB WOULD UNDERSTAND THE IMPORTANCE OF THESE ADVISORIES. THE AIM DEVOTES 7 PAGES TO WAKE TURB. NOWHERE IN THERE DOES IT REF THIS SIT. IF THERE IS ANY SIT GUARANTEED TO ESTABLISH A WAKE TURB ENCOUNTER, THIS WOULD BE IT, AND MAYBE SOME GUIDELINES COULD BE ESTABLISHED, OR THOUGHT GIVEN TO SOME. THE NEW 'HVY' TRANSPORTS HAVE PARTICULARLY NASTY WAKE, AND I DON'T SEE THAT IMPROVING ANY TIME SOON. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT HE FEELS ATC WAS REMISS IN NOT ADVISING HIM OF THE GAR OF THE B747. HE COULD HAVE AT LEAST BEEN AWARE OF THE CHANGE OF FLT PATH AND ADJUSTED HIS OWN APCH ACCORDINGLY. AT LEAST HE MIGHT HAVE BEEN PREPARED FOR THE RESULTING WAKE ACTIVITY. RPTR HAS REVIEWED THE AIM AND THERE IS NO REQUIREMENT TO ADVISE THE TRAILING ACFT IN SUCH A SIT. HE FEELS THERE SHOULD BE SUCH A REQUIREMENT. RPTR ALSO FEELS THE NEWER BOEING WINGS DEVELOP MUCH GREATER WAKE THAN PREVIOUS ONES.

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.