RWY EXCURSION.

Narrative

ACFT TYPE BA-3201 EXECUTED A NORMAL ILS RWY 24 APCH AT UNV TO TOUCHDOWN AT FLAPS 20 DEGS REF SPD MINUS 4 KTS (112 KTS). BRAKING ACTION RPTED FAIR TO POOR BY DHC-8 AND PASSED BY NEW YORK ARTCC 10 MINS PRIOR TO TOUCHDOWN. TOUCHDOWN OCCURRED 1500 FT FROM RWY THRESHOLD. PF APPLIED FULL REVERSE THRUST AND EQUAL MODERATE BRAKE PRESSURE; THEN DIFFERENTIAL BRAKE PRESSURE TO CTL R YAW. RWY SURFACE UNPLOWED; COVERED BY 1/2 INCH FRESH; LOOSE; DRY SNOW. WITH 500 FT REMAINING BRAKE PRESSURE WAS INCREASED; AIRSPD AT THIS POINT WAS 40 KTS. ACFT YAWED R AND L NOSEWHEEL STEERING WAS APPLIED TO CORRECT. ACFT DEPARTED THE END OF THE RWY AT 15-20 KTS; AND STOPPED 20 FT LATER. EMER EVAC THROUGH MAIN CABIN DOOR WAS UNEVENTFUL. SUPPLEMENTAL INFO FROM ACN 266850: SCHEDULED BAE-3201; SVC FROM IAD TO UNV. -X 900 BROKEN; 1400 OVCST; 15 F; WIND CALM; TEMP 25; DEWPOINT 22. LNDG FLAPS WERE BRIEFED FOR 20 DEGS BECAUSE ICING CONDITIONS WERE ENCOUNTERED DURING THE DSCNT TO THE INITIAL APCH ALT OF 4000 FT. ZNY ALSO ISSUED A REVISED WX RPT OF -X 1100 OVCST; 15 F; TEMP 25; DEWPOINT 22; WIND 030 DEGS AT 5 KTS. AT APPROX 50 FT AGL; THE PNF CALLED REF +10. THE ACFT TOUCHED DOWN AT REF -4; ON CTRLINE APPROX 500 FT PRIOR TO THE 3000 FT REMAINING MARKER. THE SURFACE OF THE RWY APPEARED UNPLOWED WITH THE TRACKS FROM THE PREVIOUS LNDG COVERED BY SNOW AND NOT VISIBLE TO THE CREW. WHEN THE WHEELS TOUCHED DOWN; THE PF PLACED THE PROPS INTO FULL REVERSE PITCH AND APPLIED MODERATE BRAKING TO KEEP THE ACFT TRACKING DOWN THE CTRLINE. THE PF DETERMINED AT THIS POINT THAT BRAKING ACTION WAS NIL AND JUDGED THAT ADDITIONAL BRAKING WOULD HAVE PRODUCED AN UNCTLABLE; HIGH SPD YAW. WHEN ARPT CONDITIONS ARE RAPIDLY CHANGING; THE ARPT SHOULD FREQUENTLY CHK RWY CONDITIONS TO PREVENT SUCH RECURRENCES. BY THE TIME THE CREW WAS AWARE OF THE NIL BRAKING CONDITIONS; GAR WAS NOT POSSIBLE.