A CAMERON A120 BALLOON PLT MAKES AN UNPLANNED HARD LNDG INTO A GROVE OF TREES DURING AN ENCOUNTER WITH A LOW ALT WINDSHEAR; SLIGHTLY INJURING OR SHOCKING SEVERAL OF HIS PAX NEAR PAE; WA.

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ON 07/FRI/02; I CHKED WX USING BOTH A DUAT BRIEFING AND ADDITIONAL WX INFO VIA THE INTERNET. WITHIN 45 MINS PRIOR TO FLT; I CONFIRMED THE NEAREST RPTING STATIONS SURFACE WINDS AND LAUNCHED SEVERAL HELIUM FILLED BALLOONS TO TEST THE UPPER LEVEL WINDS. ALL HELIUM BALLOONS INDICATED GENTLE; LESS THAN 10 MPH WINDS AT ALTS ESTIMATED THROUGH 5000 FT AGL. ABOVE 1000 FT THERE WAS A TURN TO THE R (S) OF ABOUT 60 DEGS. THE RPTED AND OBSERVED DATA APPEARED TO BE NORMAL FOR THE TIME OF DAY AND ATMOSPHERIC CONDITIONS. THE BALLOON; A 120000 CUBIC FT; DOUBLE BURNERS; COMMERCIAL RIDE OP WITH 6 PAX AND PLT; WAS PREPARED FOR LAUNCH. PRIOR TO TKOF; PAX WERE GIVEN A NORMAL PREFLT BRIEFING OF WHAT TO EXPECT DURING THE FLT AND ON LNDG. BOTH A CALM; EXPECTED; AND WINDY LNDG BRIEFING WAS GIVEN TO THE PAX. PRIOR TO LAUNCH THERE WAS SOME SLIGHT INCREASE IN SURFACE WIND SPD WHICH IS NOT UNCOMMON FOR THE LOCATION AND TIME OF DAY. ON LAUNCH THE BALLOON ASCENDED RAPIDLY TO ALT FOR VIEWING THE SURROUNDING AREA. MAX HT DURING THE FLT WAS 4300 FT AGL. WIND AT ALT WAS LESS THAN 10 MPH. HOWEVER; IT WAS OBSERVED THAT THE SURFACE WINDS HAD INCREASED SIGNIFICANTLY. FORECASTED SURFACE WINDS WERE FOR 6 KTS THROUGHOUT THE FLT PERIOD. AS THE BALLOON APCHED THE ANTICIPATED LNDG AREA A DSCNT WAS INITIATED AND ONCE BELOW 1000 FT AGL; THE FORWARD SPD INCREASED TO 10-15 MPH. THE BALLOON CONTINUED ON COURSE FOR A LNDG FIELD FREQUENTLY USED. THE FLT DIRECTION WOULD REQUIRE XING A RIVER; A STAND OF WOODS; THEN THE INTENDED FIELD FOR LNDG. BECAUSE OF THE INCREASED WIND SPD; IT WAS ANTICIPATED THAT POTENTIAL TURB AND/OR WINDSHEAR MIGHT BE PRESENT NEAR THE SURFACE; AND ESPECIALLY ONCE CLRING THE LAST TREES AND DSNDING INTO THE FIELD. ALSO BASED ON PREVIOUS EXPERIENCE A L TURN MIGHT BE PRESENT VERY NEAR THE TOPS OF THE TREES. WITH THESE CONSIDERATIONS IN MIND; A LONG; SLOW DSCNT RATE APCH WAS ESTABLISHED. THIS WAS DONE BECAUSE A SHORT STEEP APCH WOULD REQUIRE A HIGH RATE OF DSCNT AND WOULD NOT ALLOW ADEQUATE TIME TO RECOVER FROM SUDDEN WIND CHANGES CAUSED BY WINDSHEARS. AS THE BALLOON CROSSED THE RIVER; APPROX 350 FT ABOVE IT DSNDING AT 100-200 FPM; IT ENTERED THE AREA OF THE WOODS BTWN THE RIVER AND THE INTENDED LNDG FIELD; APPROX 500 FT IN WIDTH. THE BALLOON WAS ON COURSE AND ON GS. SUDDENLY THE BALLOON ENCOUNTERED A WINDSHEAR. I RECOGNIZED IT AND IMMEDIATELY TOOK CORRECTIVE ACTION BY TURNING ON BOTH BURNERS. IN LOOKING UP TO ENSURE THAT THE HEAT WAS GOING UP; I OBSERVED THAT BOTH FLAMES WERE BENT AT A 90 DEG ANGLE FROM THE FORCE OF THE WINDSHEAR. AS A RESULT OF THE SHEAR; THE BALLOON LOST SOME LIFT AND TURNED APPROX 30 DEGS TO THE L. IT WAS NOW ON A COURSE WITH A STAND OF COTTONWOOD TREES. CONTACT WAS MADE RESULTING IN FABRIC; BUT NOT STRUCTURAL DAMAGE. THE BALLOON WAS LANDED IMMEDIATELY IN THE VICINITY; IN PART BECAUSE OF THE LOSS OF LIFT. THE LNDG WAS GENTLE AND THE BALLOON WAS AT EQUILIBRIUM. IT WAS DETERMINED THAT THE LNDG SITE WAS A SAFE AND STABLE LOCATION AND THE BALLOON WAS DEFLATED. PAX WERE CHKED FOR INJURIES; ONLY 2 MINOR BUMPS AND 1 SKINNED HAND; EVACED FROM THE BASKET AND TREATED FOR SHOCK. IN POSTFLT ANALYSIS; THE CAUSE OF THE MISHAP IS RELATED TO THE WINDSHEAR. THE QUESTION IS: COULD THIS SHEAR AND/OR ITS STRENGTH HAVE BEEN ANTICIPATED? 2 DAYS EARLIER; THE PLT MADE AN ALMOST IDENTICAL APCH UNDER SIMILAR METEOROLOGICAL CONDITIONS TO THE SAME FIELD WITH THE SAME FLT PROFILE AND DIRECTION. THAT LNDG WAS WITHOUT INCIDENT AND ONCE BEHIND THE TREE LINE; A CALM LNDG. THE SURFACE WIND ON THIS FLT WAS STRONGER THAN ANY PREVIOUS LNDGS TO THIS FIELD OVER THIS FLT RTE. WHILE SOME WINDSHEAR COULD BE; AND WAS; ANTICIPATED; THE STRENGTH OF IT WAS NOT. IN REVIEWING THE FLT AND WIND CONDITIONS WITH OTHER PLTS WE HAVE RE-EXAMINED AND DETERMINED THAT WIND SPDS BEYOND A CERTAIN AMOUNT MAKE THIS AREA LESS SUITABLE FOR ATTEMPTING A LNDG. THUS; WE HAVE ISSUED NEW GUIDELINES FOR PLTS FLYING IN THE AREA THAT IF THE SURFACE WINDS ARE MORE THAN 10 MPH NOT TO ATTEMPT A LNDG IN THIS FIELD BECAUSE OF THE POTENTIAL SEVERITY OF WINDSHEAR.