INFLT MICROBURST ENCOUNTER. RPTR PLT; TOWING A BANNER AND FLYING AT 1300 FT AGL HIT STRONG DOWNDRAFT; LOST 1000 FT. PLT FLEW OUT OF IT AND REGAINED ALT; BUT DIVERTED AROUND OTHER MICROBURSTS TO RETURN TO HIS HOME ARPT. WX FACTORS STRONG DOWNDRAFT; MICROBURST.

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BTWN XA35 AND XA53 PM; BTWN APA AND DOWNTOWN DENVER I ENCOUNTERED A STRONG DOWNDRAFT. I WAS PULLING A BANNER AT 6500 FT MSL WHEN IT STARTED. IT TOOK ME DOWN VERY STRONGLY (500 FPM PLUS) AND I WAS LOOKING FOR AN EMPTY AREA IN WHICH TO DROP THE BANNER. I FOUND AN UNUSED BASEBALL COMPLEX AND BEGAN CIRCLING IT PREPARATORY TO DROPPING THE BANNER AND/OR LNDG IF NECESSARY. I HAD BEEN FLYING FOR OVER 2 HRS SO I WAS LIGHTER BECAUSE OF THE FUEL USED (APPROX 96 LBS). I WOULD ESTIMATE THAT I WAS AT ABOUT 300 FT AGL AT TIMES AS I CIRCLED AT FULL PWR. I FINALLY BEGAN TO REGAIN ALT AND WAS AT ABOUT 500 FT AGL WHEN I MOVED N ABOUT 1/4 MI TO A LARGER OPEN AREA. AFTER ABOUT 10 MINS OF THIS; I HAD REGAINED 6500 FT AND CONTINUED MY FLT. I WAS TALKING TO ANOTHER BANNER TOW PLANE ON 122.75 AT THE TIME OF THIS OP AND HE TOLD ME THAT A BIG DOWNBURST HAD HIT HIM AT MILE HIGH STADIUM (NW OF ME) AND HE HAD TO LEAVE TO GET OUT OF IT. HE SAID THAT IT WAS COMING MY WAY. I WAS ALREADY IN IT WHEN HE TOLD ME THIS. THERE WERE SEVERAL DOWNBURSTS (MICROBURSTS) IN THE DENVER AREA THAT AFTERNOON. I HAD TO FLY W TO BJC IN ORDER TO RETURN FROM DOWNTOWN DENVER TO 48V (TRI- COUNTY/ERIE) TO AVOID A PARTICULARLY LARGE ONE. I DON'T KNOW WHAT I COULD HAVE DONE DIFFERENTLY TO PREVENT THIS.