PLT OF A MOONEY; MO2K; LOST CTL OF THE ACFT DURING DSCNT WHEN ENCOUNTERING SEVERE TURB CAUSING THE GYRO ATTITUDE AND HDG INDICATOR TO TUMBLE. PLT RECOVERED 5000 FT LATER AFTER BREAKING OUT OF IMC. HE THEN STAYED OUT OF THE CLOUDS AND DIVERTED TO LAND IN NIGHT VFR CONDITIONS.

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PROB WITH 1983 MOONEY MO2K/G ON SEP/XA/97. PLANE WAS ON IFR FLT PLAN FOR BTR TO CPS. 2 FULL BRIEFINGS WERE GIVEN ON THE TELEPHONE BY FAA FSS. I DELAYED MY FLT FROM XX00 TO XX40 TO LET THE WX IMPROVE. PLANE WAS APPROX 15 MI S OF FARMINGTON; MO; AT 7000 FT AT ABOUT XY00. ON THE CTLR'S ADVICE; I WAS ON A HDG OF 360 DEGS (5 DEGS W OF MY COURSE OF 5 DEGS TO CPS TO AVOID 'THE TAIL OF A TSTM CELL.' MY STORMSCOPE SHOWED NO PROBS FOR THE NEXT 100 MI ON THE 360 DEG HDG; AND NO ACTIVITY WITHIN 50 MI IN ANY DIRECTION. I REQUESTED AND WAS GIVEN PERMISSION TO DSND FROM 7000 FT TO 5000 FT IN PREPARATION FOR MY APCH TO CPS. THE PLANE RAN INTO EXTREME TURB. THE ARTIFICIAL HORIZON STARTED SPINNING COMPLETE CIRCLES. I WAS IN THE CLOUDS. I USED PRIMARY INSTS IN ORDER TO ASSESS MY ATTITUDE. SPD WAS NEAR THE RED LINE AND I WAS DSNDING AT OVER 2000 FPM. THE LNDG GEAR WAS LOWERED IN ORDER TO SLOW THE AIRPLANE. AT THIS POINT; I DECLARED AN EMER. WHEN I MADE VISUAL CONTACT WITH THE GND; AT 2000 FT ASL; I WAS ABLE TO STABILIZE THE ATTITUDE OF THE PLANE. THE GEAR WOULD NOT RETRACT; BUT INSTEAD POPPED THE CIRCUIT BREAKER. THE HSI SHOWED A READING 90 DEGS E OF THE ACTUAL HDG (FROM THE COMPASS AND THE GPS). WHEN I REGAINED FULL CTL OF THE AIRPLANE; I ELECTED TO CLB NO HIGHER THAN 3000 FT; SINCE I HAD NO CONFIDENCE IN THE ARTIFICIAL HORIZON; AND WOULD NOT CLB INTO INST CONDITIONS. I WENT TO A MORE WESTERLY HDG TO AVOID AREAS OF LIGHTNING. I FLEW THE AIRPLANE USING THE GPS TO SUS; WHICH HAD LIGHTS; AN ACTIVE TWR; AND EMER EQUIP. I FEEL RECENT RECURRING TRAINING HELPED ME TO DEAL WITH THIS SIT EFFECTIVELY. IN ADDITION; I WILL BE LESS WILLING TO FLY IFR IN IMC CONDITIONS AT NIGHT.