Narrative:

We were following an air carrier 747. TCASII placed the 747 about 5 1/2 - 6 mi in front of us. We appeared to be co-equal airspeed at about 130-135 KIAS. We did encounter some wake turbulence at about 10 mi out because we were intercepting the GS from a level altitude which put us below the 747's intercept and glide path. We expected this and then adjusted our glide path to stay above the wake turbulence zone. Approaching the 2.7 idgu fix we noted a series of ripples and 2 accompanying water spouts or water devils (in contrast to a dust devil). I will diagram this on the attachment. I feel the significant of this observation is to help confirm previous research. From position, speeds, etc, I estimate that it took the 747's vortices about 1 1/2 mins to descend 400 ft to the water surface. Callback conversation with reporter revealed the following information: reporter mainly wanted to state the observation he had with the water funnels rising along the B747 ground track. The flight crew did encounter some wake turbulence from the preceding aircraft but it was not strong. The same pattern is here as in other observation he encountered with wake, which is descending a heavy aircraft down to his altitude. Because he knew what could happen in such a situation, he slowed for greater separation and braced for a possible upset. However, the encounter that affected his aircraft was small, probably because of a light crosswind.

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Original NASA ASRS Text

Title: WAKE TURB ENCOUNTER AND OBSERVATION OF WAKE TURB EFFECTS ALONG GND TRACK.

Narrative: WE WERE FOLLOWING AN ACR 747. TCASII PLACED THE 747 ABOUT 5 1/2 - 6 MI IN FRONT OF US. WE APPEARED TO BE CO-EQUAL AIRSPD AT ABOUT 130-135 KIAS. WE DID ENCOUNTER SOME WAKE TURB AT ABOUT 10 MI OUT BECAUSE WE WERE INTERCEPTING THE GS FROM A LEVEL ALT WHICH PUT US BELOW THE 747'S INTERCEPT AND GLIDE PATH. WE EXPECTED THIS AND THEN ADJUSTED OUR GLIDE PATH TO STAY ABOVE THE WAKE TURB ZONE. APCHING THE 2.7 IDGU FIX WE NOTED A SERIES OF RIPPLES AND 2 ACCOMPANYING WATER SPOUTS OR WATER DEVILS (IN CONTRAST TO A DUST DEVIL). I WILL DIAGRAM THIS ON THE ATTACHMENT. I FEEL THE SIGNIFICANT OF THIS OBSERVATION IS TO HELP CONFIRM PREVIOUS RESEARCH. FROM POS, SPDS, ETC, I ESTIMATE THAT IT TOOK THE 747'S VORTICES ABOUT 1 1/2 MINS TO DSND 400 FT TO THE WATER SURFACE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR MAINLY WANTED TO STATE THE OBSERVATION HE HAD WITH THE WATER FUNNELS RISING ALONG THE B747 GND TRACK. THE FLC DID ENCOUNTER SOME WAKE TURB FROM THE PRECEDING ACFT BUT IT WAS NOT STRONG. THE SAME PATTERN IS HERE AS IN OTHER OBSERVATION HE ENCOUNTERED WITH WAKE, WHICH IS DSNDING A HVY ACFT DOWN TO HIS ALT. BECAUSE HE KNEW WHAT COULD HAPPEN IN SUCH A SIT, HE SLOWED FOR GREATER SEPARATION AND BRACED FOR A POSSIBLE UPSET. HOWEVER, THE ENCOUNTER THAT AFFECTED HIS ACFT WAS SMALL, PROBABLY BECAUSE OF A LIGHT XWIND.

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.