Narrative:

We were approximately 6 mi south of atl heading west on radar vectors on a downwind leg to land on runway 9R at atl. We were descending from 11000 ft to 3500 ft. Approach control advised us that we were behind a heavy L1011 on the downwind. We were IMC, between layers, and our TCASII was inoperative, so I had no idea just where the L1011 was. We encountered the wake turbulence at approximately 5200 ft MSL. The aircraft encountered light turbulence then a roll to the left of approximately 20 degrees then a roll back to the right at 30 degrees along with a slight pitch up tendency. I then asked the controller for vectors away from the L1011's flight path. As I mentioned, I could not see the traffic, for when I can see preceding traffic, I will make slight heading changes to stay clear of a 'wake path' ahead. In this case also, I thought that the winds aloft were stronger than they apparently were and that the wind would 'break up' the wake. Atl is ripe for these sits, as the jets are on initial downwind leg at 12000 ft and propellers are at 11000 ft, so at some point there is an altitude 'crossover.' callback conversation with reporter revealed the following information: this reporter was flying an EMB120 and hit the wake of an L1011. The flight conditions were IMC with layered clouds at the time of the event. He said that he would have offset his route if he had been able to see the L1011 ahead of him. He was not aware of its location until after he reported hitting the wake to the approach controller. The reporter said that he was already disturbed that the TCASII was inoperative, but he now believes that it may have assisted him in avoiding the wake if he could have used it to, at least, see that an aircraft was just ahead of him. He further said that the normal practice of bringing all aircraft over the same ground tracks with the heavier aircraft descending through the altitudes of the lighter aircraft made the likelihood of an encounter quite high. Once he had realized the situation, the reporter stayed high and offset to avoid the wake.

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Original NASA ASRS Text

Title: THIS EMB120 FLC HIT THE WAKE OF AN L1011 WHILE BEING VECTORED ON DOWNWIND AND DSNDING FOR RWY 9R AT ATL. THE FLC WAS AWARE OF THE L1011, BUT NOT ITS EXACT LOCATION BECAUSE THEIR TCASII WAS INOP.

Narrative: WE WERE APPROX 6 MI S OF ATL HEADING W ON RADAR VECTORS ON A DOWNWIND LEG TO LAND ON RWY 9R AT ATL. WE WERE DSNDING FROM 11000 FT TO 3500 FT. APCH CTL ADVISED US THAT WE WERE BEHIND A HVY L1011 ON THE DOWNWIND. WE WERE IMC, BTWN LAYERS, AND OUR TCASII WAS INOP, SO I HAD NO IDEA JUST WHERE THE L1011 WAS. WE ENCOUNTERED THE WAKE TURB AT APPROX 5200 FT MSL. THE ACFT ENCOUNTERED LIGHT TURB THEN A ROLL TO THE L OF APPROX 20 DEGS THEN A ROLL BACK TO THE R AT 30 DEGS ALONG WITH A SLIGHT PITCH UP TENDENCY. I THEN ASKED THE CTLR FOR VECTORS AWAY FROM THE L1011'S FLT PATH. AS I MENTIONED, I COULD NOT SEE THE TFC, FOR WHEN I CAN SEE PRECEDING TFC, I WILL MAKE SLIGHT HDG CHANGES TO STAY CLR OF A 'WAKE PATH' AHEAD. IN THIS CASE ALSO, I THOUGHT THAT THE WINDS ALOFT WERE STRONGER THAN THEY APPARENTLY WERE AND THAT THE WIND WOULD 'BREAK UP' THE WAKE. ATL IS RIPE FOR THESE SITS, AS THE JETS ARE ON INITIAL DOWNWIND LEG AT 12000 FT AND PROPS ARE AT 11000 FT, SO AT SOME POINT THERE IS AN ALT 'CROSSOVER.' CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THIS RPTR WAS FLYING AN EMB120 AND HIT THE WAKE OF AN L1011. THE FLT CONDITIONS WERE IMC WITH LAYERED CLOUDS AT THE TIME OF THE EVENT. HE SAID THAT HE WOULD HAVE OFFSET HIS RTE IF HE HAD BEEN ABLE TO SEE THE L1011 AHEAD OF HIM. HE WAS NOT AWARE OF ITS LOCATION UNTIL AFTER HE RPTED HITTING THE WAKE TO THE APCH CTLR. THE RPTR SAID THAT HE WAS ALREADY DISTURBED THAT THE TCASII WAS INOP, BUT HE NOW BELIEVES THAT IT MAY HAVE ASSISTED HIM IN AVOIDING THE WAKE IF HE COULD HAVE USED IT TO, AT LEAST, SEE THAT AN ACFT WAS JUST AHEAD OF HIM. HE FURTHER SAID THAT THE NORMAL PRACTICE OF BRINGING ALL ACFT OVER THE SAME GND TRACKS WITH THE HEAVIER ACFT DSNDING THROUGH THE ALTS OF THE LIGHTER ACFT MADE THE LIKELIHOOD OF AN ENCOUNTER QUITE HIGH. ONCE HE HAD REALIZED THE SIT, THE RPTR STAYED HIGH AND OFFSET TO AVOID THE WAKE.

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.