RWY EXCURSION.

Narrative

ABOUT 12-15 MINS OUT FROM SPI THE FO PICKED UP THE LCL ATIS AND PASSED IT ON TO ME. I NOTED THAT THERE WAS LIGHT FREEZING RAIN AND DRIZZLE WITH THE WIND AT 100 DEGS; 5 KTS. BRAKING ACTION WAS RPTED POOR ON RWY 4 BY AN SMT. I CALLED DISPATCH AND CHKED TO BE SURE WE COULD LAND IN LIGHT FREEZING RAIN. THE DISPATCHER SAID IT WAS OK TO DO SO. APCH CTL OFFERED US RWY 22 IF WE WANTED IT BUT I CHOSE TO STAY WITH RWY 4 DUE TO THE POOR BRAKING RPT AND THE FACT THAT THE WIND OF 100 DEGS FAVORED RWY 4 WHEREAS RWY 22 WOULD HAVE GIVEN US A TAILWIND. CHKLISTS WERE RUN AND APCH BRIEF WAS COMPLETED. THE ILS APCH AND LNDG ON CTRLINE WAS NORMAL IN ALL RESPECTS WITH BREAKOUT AT APPROX 300 FT AND EXCELLENT VISIBILITY BELOW THE CLOUDS. THERE WAS NEGATIVE ICE ON THE AIRPLANE. WE ASKED HOW OLD THE BRAKING ACTION RPT WAS AND WERE TOLD IT WAS 15 MINS OLD. FO ASKED FOR A 180 DEG TURN ON THE RWY AS WE RPTED BRAKING AS FAIR; WHICH IT WAS ON THE CTR OF THE RWY. THE TURN WAS APPROVED BY TWR. I SLOWED THE PLANE TO ALMOST A STOP AND STEERED THE PLANE TO THE R TO GIVE MYSELF MORE ROOM TO MAKE A L 180 DEG TURN. DURING THE L TURN AT A SPD BELIEVED TO BE LESS THAN 365 KTS IT BECAME APPARENT THAT THE PLANE WAS SLIDING AND THAT WE COULD NOT COMPLETE THE TURN BEFORE GOING OFF OF THE W SIDE OF THE RWY. I TRIED TO STOP THE PLANE BUT WAS UNABLE TO DO SO BEFORE WE SLID OFF OF THE RWY INTO THE SNOW AT AN APPROX HDG OF 220 DEGS. I SET THE PARKING BRAKE AND FEATHERED THE ENGS. I INSTRUCTED FO TO INFORM THE TWR OF OUR PROB WHILE I CALLED DISPATCH. I THEN ASKED FO TO TELL THE PAX TO REMAIN SEATED AND TELL THEM WHAT HAD OCCURRED. THE GND EQUIP ARRIVED ALMOST IMMEDIATELY AND IN 10-20 MINS A BUS ARRIVED AND THE PAX WERE DEPLANED AFTER THOROUGH SANDING OF THE AREA AT THE BOTTOM OF THE STAIRS DUE TO THE FACT THAT IT WAS NEAR IMPOSSIBLE TO REMAIN UPRIGHT AND WALK ON THAT AREA OF THE RWY. I INSTRUCTED THE FA TO ACCOMPANY THE PAX IN ORDER TO BE OF ANY ASSISTANCE TO THEM THAT HE COULD. IT SHOULD BE NOTED THAT THE GND PERSONNEL INVOLVED IN REMOVING THE PLANE HAD GREAT DIFFICULTY IN MAINTAINING THEIR FOOTING. AN FAA MAN CAME ON BOARD AND REQUESTED OUR LICENSE AND MEDICALS WHICH WE FURNISHED AFTER HE PROPERLY IDENTED HIMSELF. FO AND I REMAINED ON THE PLANE AT ALL TIMES AFTER THE INCIDENT AND SHUTDOWN AND UNTIL THE PLANE WAS TOWED TO AND PARKED AT THE GATE. AFTER PARKING AT THE GATE WE COMPLETED THE LEAVING ACFT CHKLIST AND DEPLANED.