MLG SLIDES OFF TXWY AFTER LNDG WHEN THEY DISCOVER THE BRAKING ACTION IS NIL.

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ON APCH TO 35R AT OKC BRAKING ACTION RPTED AS FAIR TO POOR. MADE A FIRM TOUCHDOWN 1000 FT DOWN RWY TO HELP ESTABLISH BRAKING AND USED FULL REVERSE. BRAKING ACTION WAS NIL FOR THE ENTIRE RWY. ROLLED THE AIRPLANE TO END; TURNED OFF ONTO TXWY AND LOST ALL DIRECTIONAL CTL. I ELECTED TO SHUT DOWN BOTH ENGS PRIOR TO LEAVING THE TXWY TO AVOID ANY FIRE OR DAMAGE TO AIRPLANE AND INJURY TO PAX. THE ACFT WAS NOT DAMAGED AND NO INJURIES OCCURRED. I FEEL A CONTRIBUTING FACTOR WAS ATC LACK OF INFO ON ARPT CONDITIONS. PRIOR TO OUR ARR 2 ACFT HAD SLID OFF THE TXWY. THIS INFO WOULD HAVE BEEN EXTREMELY HELPFUL IN MY DECISION TO CONTINUE THE APCH AND EXIT THE RWY. IT ALSO TOOK 2 HRS TO GET THE PEOPLE OFF THE AIRPLANE DUE TO LACK OF EMER EQUIP AND FIELD CONDITIONS. ANOTHER CONTRIBUTING FACTOR WAS A SHORT DELAY GIVEN TO US BY ATC TO ALLOW DEPS OFF THE RWY SO THEY DID NOT HAVE TO RETURN TO THE GATE TO GET DEICED. I ALSO FEEL I COULD HAVE DONE A BETTER JOB ON INQUIRY INTO FIELD CONDITIONS I DID CHK NOTAMS AND DID ASK APCH LATEST BRAKING RPTS. I WOULD LIKE TO SEE MORE INFO PROVIDED BY ATC EARLIER IN FLT TO FACILITATE BETTER DECISION ON THE PART OF THE PLTS. (NOTE; A BRAKING ACTION RPT OF POOR TO NIL WAS GIVEN TO US WHILE WE WERE ON THE RWY PAST MOST OF THE USABLE EXITS). SUPPLEMENTAL INFO FROM ACN 232605: ON BASE LEG TWR ADVISED BRAKING ACTION FAIR TO POOR (NO MENTION OF 1/2 INCH OF ICE COVERING AIRFIELD). HALFWAY DOWN RWY TWR ADVISED BRAKING ACTION POOR TO NIL; RPTED BY SIMILAR TYPE ACFT; WITH WORSE BRAKING AT N END -- AHEAD OF US. AT THIS POINT THE ACFT STARTED SLIDING SIDEWAYS OFF THE N SIDE OF THE TXWY. WHEN I ADVISED TWR WHAT HAD HAPPENED TWR ADVISED ARPT RESPONSE WOULD BE DELAYED AS ALL AVAILABLE EQUIP WAS RESPONDING TO A JET THAT HAD SLID OFF A TXWY WHILE TAXIING OUT TO TKOF 15 MIN BEFORE WE LANDED. QUESTION: WHY WERE WE NOT TOLD ABOUT THIS BEFORE LNDG AND WHY WAS THE AIRFIELD NOT CLOSED AT THAT POINT??? SIMPLY PUT; WE WERE NOT GIVEN ALL THE INFO AVAILABLE TO THE TWR. TWR SHOULD HAVE ADVISED US BEFORE LNDG THAT THE FIELD WAS COVERED WITH A SHEET OF ICE AND THAT ANOTHER ACR HAD SLID OFF THE TXWY. ALSO; STATING THAT A RAINSHOWER HAD JUST PASSED OVER THE FIELD WOULD HAVE BEEN VERY USEFUL INFO. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR CONFIRMED THAT NO PAX WERE INJURED. HE WAS VERY DISAPPOINTED IN THE SVC PROVIDED BY ATC AT OKC THAT NIGHT.