LOSS OF ACFT CTL WHEN ACR MLG PERFORMS TKOF IN PROX OF TSTM ACTIVITY.

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DEP WAS FROM MCI; ACTIVE RWY HAD BEEN 19 WITH SOUTHERLY WIND FLOW. CREW WAS ATTENTIVE TO FAST MOVING TSTM APCHING FROM THE NW -- A SINGLE BUT LARGE CELL CONTOURING ON RADAR WHEN CREW ARRIVED AT ARPT; DISTANCE APPROX 15-20 MI FROM ARPT. TURN TIME WAS ONLY 15 MINS OR SO AND ACFT PUSHED BACK FOR DEP. THE CELL WAS NOW 5-7 MI FROM ARPT AND WINDS HAD SHIFTED TO WNW AND RWY 27 WAS ACTIVE. CREW REQUESTED AND RECEIVED CLRNC FOR IMMEDIATE L TURN TO 180 DEG HDG AFTER TKOF. WINDS WERE LIGHT AND STEADY AND TKOF WAS INTO CLR AIR; NO RAIN; WITH CLOUDS OUTCROPPING FROM CELL AT APPROX 2000 FT AGL. SKY WAS CLR TO S. NORMAL TKOF WAS MADE BUT ADVERSE CONDITION PROFILE WAS USED AS PRECAUTION WITH FLAPS RAISED EARLIER THAN NORMAL PROFILE AND INITIAL CLB SPD OF 210 KTS ESTABLISHED. CAPT FLYING WAS ATTEMPTING TO MAKE L TURN AS ASSIGNED WITH SIGNIFICANT FORCES APPLIED TO YOKE BUT NO ROLL RESPONSE; EVEN TO THE POINT FO STATED 'YOU BETTER START THE L TURN' AND CAPT REPLIED 'I'M TRYING.' SEVERAL SECONDS PASSED BEFORE ROLL RESPONSE ALLOWED THE L TURN. PASSING APPROX 220 TO 230 DEG HDG; MODERATE TURB WAS ENCOUNTERED AND ACFT WAS ACCELERATED TO 230 KTS AND ROLL RATE/TURN RATE DECREASED TO ALLOW FOR AIRSPD INCREASE. SOME GUSTS WERE ENCOUNTERED AT THIS POINT AND WE WERE PROBABLY 1000-1200 FT AGL. SOMEWHERE AROUND 200 DEG HDG; WITH CONSTANT PITCH ANGLE; AIRSPD INCREASED TO OVER 300 KTS INSTANTANEOUSLY AND VERT SPD BECAME INDETERMINABLE AS IVSI'S WERE COMPLETELY PEGGED AT 6000 FPM RATE OF CLB. AT THIS POINT RIDE WAS FAIRLY SMOOTH AND COORD EXISTED TO SOME 3000 FT AGL OR MORE. ASTONISHED CREW TRIED TO ANALYZE THE EVENTS AND DECIDED THAT IMMEDIATELY AFTER TKOF THE R WING MUST HAVE BEEN CAUGHT IN A SEVERE DOWNDRAFT PREVENTING THE ROLL TO A TURN; THEN TURB ENCOUNTERED BTWN THE DOWNDRAFT AND OUTFLOW AND THEN AIRSPD INCREASE OF 70-180 KTS OCCURRED ENTERING THE HORIZ VORTEX. UPDRAFT SPD; AS STATED; WAS IMMEASURABLE BUT UNBELIEVABLE. OBVIOUSLY; WE WERE VERY FORTUNATE. NO DOUBT EXISTS IN MY MIND THAT HAD WE ENCOUNTERED THE SAME CIRCUMSTANCES IN REVERSE; IE; 70- 100 KTS AIRSPACE LOSS AND EXTRAORDINARY DOWNWARD DRAFT FORCES; IT WOULD HAVE BEEN IMPOSSIBLE FOR THIS ACFT OR ANY OTHER TO HAVE FLOWN THROUGH THE ENCOUNTER OR SURVIVED.