AN ACR ACFT DISPATCHED TO AN ARPT WITH MU READINGS OF 25/18/22 RAN OFF THE END OF THE RWY WITH ACTUAL NIL BRAKING.

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WE OPERATED ZZZ1 TO ZZZ2. THE ZZZ1 OP WAS RUNNING LATE DUE TO EXTREME WX AT ZZZ2 AND SINGLE RWY OPS. THE FO OPERATED INBOUND ZZZ3 TO ZZZ1. I WAS BEGINNING THE TRIP AND HAD DRIVEN UP FROM MY HOME; A 3 HR DRIVE. THE FO ARRIVED AT OPS WITH 45 MINS LEFT TILL BLOCK OUT. I ARRIVED APPROX 1 HR PRIOR TO SHOW TO CHK V-VILE; DO REVISIONS; ETC. ABOUT 70 MINS PRIOR TO SCHEDULED DEP; I GOT PAPERWORK TO BEGIN FLT PLANNING. AS I WAS AWARE OF WX CONDITIONS DUE TO WX CHANNEL BROADCAST; I WAS ESPECIALLY INTERESTED IN ARPT CONDITIONS AT ZZZ2. THE DEST ARPT DETAILED INFO SECTION LISTED RWY 6/24 CONDITIONS AS THN IR SA WEF MU 25/18/22 FORECAST WAS 27020G32KTP6SM SCT025 FM 0800 30015G25KT P6SM SCT035. THOUGH RWY CONDITIONS WERE POOR; WE COULD STILL BE DISPATCHED PER THE FOM. WHEN THE FO FINALLY ARRIVED; WE BRIEFLY DISCUSSED THE PAPERWORK; WITH PRIMARY CONCERNS ABOUT GETTING OUT TO THE ACFT FOR PREFLT. THE SORT RAN APPROX 1 HR LATE ANYWAY; BUT THE FLT WAS NORMAL AND UNEVENTFUL. WHILE ENRTE; WE SPOKE AT LENGTH ABOUT ZZZ2 CONDITIONS; AVAILABLE APCHS; ETC. THE FO HAD ONLY BEEN INTO ZZZ2 THE NIGHT BEFORE FOR THE FIRST TIME; AND THIS WAS MY FIRST TIME OPERATING INTO ZZZ2. IN ADDITION TO THE RWY SURFACE AND WIND CONDITIONS; WE WERE UNFAMILIAR WITH THE ARPT; AND IT WAS AN UNCTLED FIELD AT THE TIME OF OUR ARR. THE FO STARTED GIVING CTAF POS RPTS AT ABOUT 40 MI OUT. WINDS FAVORED RWY XX AT 28013G20. WE SET UP FOR THE RWY XX LOC BCR APCH; AND EVEN THOUGH IT WAS VMC; I GAVE A FULL BRIEFING FOR THE APCH AS IT WAS NIGHT AND WE WERE BOTH UNFAMILIAR WITH THE FIELD. BEFORE TOP OF DSCNT; I BRIEFED THE APCH WITH EXTRA EMPHASIS ON THE WIND CONDITIONS. V SPDS WERE 125/165/205. I RECOMMENDED A BUG SPD OF 140 KTS DUE TO WIND; AND I BRIEFED THAT I WOULD CARRY THE ADDITIVE WITH THE AUTOTHROTTLES ON. WE WERE CONFIGURED BY FAF AND BEGAN OUR DSCNT ON THE VNAV PATH. I RECALL BIASING THE HIGH SIDE OF THE VASI; AND CROSSED OVER THE RWY THRESHOLD BTWN 50-100 FT. I WOULD SAY I WAS CLOSER TO 100 FT. THE APCH WAS STABILIZED AT 1000 FT AGL AND I STATED SO WHEN I CALLED THE RWY IN SIGHT. BELOW 200 FT; THE CONDITIONS WERE VERY GUSTY; BUT THE APCH REMAINED STABILIZED. AT ONE POINT; WE EXPERIENCED A 10 KT INCREASE IN AIRSPD. WITH THE EXTRA AIRSPD ADDITIVE; PLUS THE WIND GUST; WE DID FLOAT A BIT OVER THE TOUCHDOWN ZONE; LNDG AT THE FAR END. WITH R QUARTERING HEADWINDS; I TOUCHED DOWN R MAIN FIRST. AFTER NOSEWHEEL TOUCHDOWN; I FULLY DEPLOYED THE REVERSERS. AUTOBRAKES WERE SET AT 2. DECELERATION AT THIS POINT WAS NORMAL. I STOWED THE REVERSERS ON SCHEDULE AND SHORTLY THEREAFTER RELEASED THE AUTOBRAKES. SINCE THE TXWY TURNOFF TO THE RAMP WAS AT THE VERY END OF RWY XX; AND ASSUMING WE WERE PAST THE WORST PART OF THE ICING PER THE MU RPT; I LET THE ACFT JUST SLOW ON ITS OWN. WITH ABOUT 2000 FT REMAINING AND BELOW 40 KTS GS; DECELERATION STILL SEEMED NORMAL. AS I APCHED THE TXWY; AND WITH ABOUT 400-500 FT REMAINING; I BEGAN TO APPLY BRAKES TO MAKE THE TURN. THERE WAS NO RESPONSE. IT WAS AT THIS POINT WE FIRST REALIZED THERE WERE NO BRAKES; NIL. I STATED WE DON'T HAVE ANY BRAKES. THE FO ESTIMATES GS AT THIS POINT TO BE ABOUT 10 KTS. THINKING I HAD POSSIBLE BRAKE FAILURE; I HIT THE RESERVE BRAKE SWITCH. ABOUT THAT TIME; ONE OF OUR JUMPSEATERS YELLED OUT REVERSE; REVERSE. I DEPLOYED THE T/R'S BUT IT WAS TOO LITTLE TOO LATE. ALL WE COULD DO IS RIDE THE AIRPLANE OFF THE RWY. I DID TURN THE NOSEWHEEL SLIGHTLY R THINKING THAT I COULD AT LEAST KEEP THE NOSEWHEEL FROM HITTING A THRESHOLD LIGHT. THE ACFT DID RESPOND. FORTUNATELY; THE MAIN GEAR TRUCKS MISSED THE LIGHTS AS WELL. THE AIRPLANE CAME TO A STOP AFTER THE R MAIN DEPARTED THE ASPHALT SURFACE; ABOUT 4 FROM THE EDGE. FO ESTIMATED WE DEPARTED THE RWY AT 3-4 KTS. IT WAS AT THE PACE OF A BRISK WALK. AT THIS POINT; WE STARTED THE APU; SHUT DOWN BOTH ENGS; AND CALLED ZZZ2 RADIO TO CANCEL OUR FLT PLAN AND ADVISE THAT THE ACFT WAS OFF THE RWY; AND THAT BRAKING ACTION WAS NIL. WE ALSO ASKED THEM TO ADVISE LCL ATC. IN ADDITION; IT SHOULD BE NOTED THAT THE ROLLOUT END OF THE RWY LOOKED NORMAL. THE RWY MARKINGS WERE PERFECTLY VISIBLE; AND THERE WAS NO TYPE OF GLARE FROM THE ACFT LNDG LIGHTS TO INDICATE A GLAZED SURFACE. LATER IN THE MORNING; AFTER DAYLIGHT; THE APPEARANCE OF THE SAME AREA BECAME OPAQUE AND THE THICKNESS OF THE ICE AND ACTUAL ICING CONDITIONS BECAME APPARENT. SUPPLEMENTAL INFO FROM ACN 771934: I HAVE SINCE BEEN TOLD OF AN ADVISORY CIRCULAR 91-79 THAT SAYS MU READINGS UNDER 20 ARE CONSIDERED BRAKING ACTION NIL. I WAS NOT TRAINED ON THAT AND WENT ACCORDING TO THE PUBLISHED FOM.