ATX PLT EXPERIENCES A LOSS OF ACFT CTL WITH ALTDEV ALT EXCURSION AND POS DEV WHILE IN AREA OF TSTM ACTIVITY.

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WHILST ON AN IFR FLT FROM EKM TO BRL AND 20 NM OUT FROM BRL (IN VFR CONDITIONS); CHICAGO CENTER CLRED ME TO 45000 FT ON A VISUAL TO BRL. (RPTED WX 4000 SUT 8000 OC VIS 7). WE WERE THEN CLRED TO 3000 FT AND DSNDED. MY ON BOARD RADAR INDICATED LARGE AREAS OF HVY PRECIPITATION OVER BRL. WE WERE HDG 240 DEG APPROX; AND HAD BEEN CLRED TO 2300 FT WHEN I ENCOUNTERED SEVERE TURB AHEAD OF THE STORM; AND INFORMED CENTER THAT I WAS TURNING TO A HDG OF 180. CENTER REQUESTED THAT I REMAIN WITHIN 15 DME OF BRL. I WAS UNABLE TO ESCAPE THE SEVERE TURB AND CONTINUED PAST THE 15 DME TO 20 DME TO FIND CLR AIR; AND THEN TURNED TO 360 DEG TO ASSESS THE SITUATION; AND ADVISED CENTER THAT I WOULD TRY FOR A VISUAL INTO FT MADISON. CHICAGO CENTER ADVISED A HDG OF 020 DEG AND A CLB TO 3000 FT FOR RADAR IDENT. ONCE AGAIN WE ENCOUNTERED SEVERE TURB AND CHANGED HDG TO 090 DEG; AND ADVISED CHICAGO CENTER OF MY INTENTIONS ON HDG. AT THIS POINT I REQUESTED AN APCH INTO A SMALL VFR ARPT BENEATH ME; BUT COULD NOT FIND AN IDENTIFIER FOR THIS ARPT; SO ADVISED CENTER THAT I COULD MAKE MQB BEFORE WX HIT. I WAS STILL IN SEVERE TURB AND UNABLE TO HOLD ALT DUE TO DOWNDRAFTS; MY ALT NOW 2400 FT. CENTER REQUESTED MY PRESENT ALT AND I INFORMED THEM THAT I WAS ATTEMPTING TO CLB BACK UP TO 3000 FT. THE TURB MODERATED AS WE LEFT THE VICINITY OF THE STORM AND CENTER ADVISED ME A 070 DEG HDG FOR MQB. AFTER 2 OR 3 MINS I WAS VISUAL WITH MQB; CANCELLED IFR AND LANDED. NB THE LEVEL OF TURB DURING THIS APCH PERIOD TO BRL CALLED FOR REDUCED PWR AND EXTENDED LNDG GEAR; AIRSPD FLUCTUATIONS AND BANK ANGLES PRECLUDED THE USE OF CHARTS OR PUSH BUTTON NAV EQUIP. THIS EXCURSION FROM DISTANCE AND ALT WOULD NOT HAVE OCCURRED HAD UP-TO-DATE WX INFO VIA AWOS 3 BEEN AVAILABLE TO CHICAGO CENTER; KANKAKEE; FSS AND MYSELF.