A B737-500 SLIDES OFF THE TXWY WHILE TURNING OFF THE RWY AT SDF; KY. IT WAS A 90 DEG TURN WITH BRAKING NIL. THE TWR HAD REQUESTED AN EXPEDITED CLRING; WITH TFC ON SHORT FINAL.

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I HAD ASSUMED FLT WATCH OF FLT X; MDW TO SDF. THE FLT HAD BEEN RELEASED FROM THE PREVIOUS DISPATCHER. IT HAD BEEN SNOWING IN SDF FOR FEW HRS LIGHTLY. THE FLT DEPARTED AT XA45. AT APPROX XB40 ANOTHER DISPATCHER RECEIVED A PIREP THAT BRAKING ACTION (PREVIOUSLY GOOD) WAS NOW FAIR ON RWYS AND POOR ON TXWYS AT SDF. HE HAD SENT OUT A SIT ALERT MESSAGE ON THIS. I BEGAN CHKING TO FIND ANY SDF ARRS I HAD. FLT X SHOULD HAVE BEEN ON SHORT FINAL OR ALREADY ON THE GND BY TIME FRAME. THIS FLT SEGMENT IS SHORT (50 MINS). OUR AIRLINE'S POLICY IS TO NOT CONTACT FLTS BELOW 10000 FT. I FELT HE WOULD GET THIS RPT FROM THE TWR ON APCH. I THEN TURNED MY ATTN TO MY OTHER SDF FLTS TO NOTIFY THE PLTS OF THIS NEW INFO. THERE WERE TWO OTHER FLTS THAT HAD NOT DEPARTED. I BRIEFED BOTH. APPROX XC10 I GOT MESSAGE FROM ANOTHER DISPATCHER THAT SDF OPS HAD CALLED. FLT X HAD A WHEEL IN THE MUD AND WANTED A RADIO PATCH. I CALLED HIM AND HE RPTED THAT ON HIS TURN TO TXWY G THE ACFT WENT INTO HYDROPLANE. HE ATTEMPTED THRUST REVERSE AND HIS R MAIN SLID OFF PAVEMENT INTO THE MUD. I OFFERED MY ASSISTANCE AND COORDINATED WITH OUR MAINT AND SUPERINTENDENT. HE HAD REQUESTED OUR COMPANY TUG TRY TO PULL HIM OUT. THAT WAS UNSUCCESSFUL AND OTHER ACR RECOVERY TEAM WAS CALLED. BY APPROX XD30 HE WAS PULLED OUT AND BACK TO GATE. FACTORS: THE PLTS TOLD ME THEY HAD BEEN ADVISED OF BRAKING ACTION FROM THE TWR. HE HAD ELECTED TO TURN AT TXWY G (90 DEGS) INSTEAD OF CONTINUING ONTO THE HIGH SPD TXWY EXIT (45 DEGS). THE ARPT OPS SHOULD HAVE SANDED RWYS AND TXWYS. THE USE OF ACARS WOULD HAVE SENT THE BRAKING ACTION RPT DIRECTLY TO THE COCKPIT. THE PLT HAD A FIELD CONDITION RPT GIVING BRAKING ACTION GOOD TO FAIR. COMBINED WITH 1/2 MODERATE SNOW NOW FALLING THE PLT SHOULD HAVE USED MORE CAUTION AND TAKEN THE LONGER RTE TO THE GATE VIA HIGH SPD TURN OFF. THE RELEASE WAS PLANNED WITH RWY CONDITIONS WET- GOOD. NOTAM ISSUED XD46; SDF; PATCHY THIN SNOW; BRAKING ACTION FAIR. SUPPLEMENTAL INFO FROM ACN 393301: CAPT TURNED ACFT ON 90 DEG TURN ONTO TXWY. 45 DEGS INTO TURN; ACFT SLIDES TOWARD UPWIND SIDE OF TXWY. ONLY THING COULD THINK OF HERE WAS TO STOP THE ACFT COMPLETELY ON RWY; THEN AND ONLY THEN TURN TOWARD EXITING TXWY.