BRAKING ACTION REPORT FAILED TO INCLUDE FACT LAST HALF RWY CONDITION UUNKNOWN.

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FLT WAS COMPLETING A FLT CHK OF AGC RWY 28 ILS. AT 3 MI ON FINAL THE PLT ASKED THE TWR ON BRAKING ACTION. TWR REPLY WAS 'RPTED GOOD BY AN MLG.' TWR HAD BEENADVISED THAT FLT HAD TO 6 ROLL TO THE STOP END OF THE RWY AND STOP ON THE NUMBERS FOR A FEW SECONDS TO COMPLETE THE FLT CHECK. NORMAL LNDG COMPLETED WITH A XWIND OF 50 DEG TO 18 KTS. ACFT WAS SLOWED WITH THRUST REVERSERS AND BRAKES. APPROX 1000' FROM STOP END OF RWY ADDITIONAL BRAKING WAS APPLIED TO STOP ACFT. UNKNOWN TO FLT CREW; ACFT WAS ON ICE AND STARTED TO FISH TAIL) PLT KNEW THERE WAS NO OVER RUN AND A 350' DROP AT THE END) PLT TURNED NOSE WHEEL TOWARD THE LEFT TOWARD THE LAST REMAINING TAXIWAY; ACFT TURNED SIDEWAYS AND SLID ACROSS TAXIWAY ON TO THE GND; STOPPING WITH THE TAIL OF ACFT JUST CLEAR OF RWY AND PERPENDICULAR TO RWY. RIGHT GEAR WAS IN THE MUD UP TO THE AXLE. CALLED TWR AND ADVISED THEM ACFT WAS OFF THE RWY AND STUCK IN THE MUD; WOULD THEY CALL THE FBO AND HAVE THEM SEND A TUG TO PULL ACFT OUT. THEIR REPLY WAS 'WHERE ARE YOU?' WE SAID 'OFF THE SIDE OF THE STOP END OF THE RWY;' TWR; 'OH YES; WE SEE YOU NOW.' COUNTY ARPT AUTHORITY PERSONNEL CAME TO THE ACFT AND ALSO HAD A PLOW AND SAND TRUCK START TO PLOW AND SAND THE STOP END OF RWY 28. ALL PERSONNEL WERE SLIPPING ON TAXIWAY AS IT ALSO WAS COMPLETELY COVERED WITH ICE. IT TOOK APPROX 1 HOUR TO PULL THE ACFT OUT OF THE MUD AND DURING THIS TIME; TWR CONTINUED TO LET ACFT LAND AND TAKE OFF. AGC THEN ISSUED THE FOLLOWING WX: AGC SP W 7X 1 1/2 S-F 3312 G 18/010 AGC 02/007 AGC BRAP. INCIDENT REPORT FILED WITH AEA FSDO-03 AT AGC. RECOMMENDATIONS: 1) TWR PERSONNEL; WHEN GIVING RWY CONDITIONS; I.E.; BRAKING ACTION; SHOULD GIVE IT FOR THE ENTIRE LENGTH OF RWY AND NOT JUST THE LANDING END. IF UNKNOWN; TWR PERSONNEL SHOULD REQUEST ARPT AUTHORITIES TO CHECK THE RWY WITH A VEHICLE. 2) ALTHOUGH RWY 10 (STOP END OF 28) IS NOT USED FOR LNDG AS OFTEN AS RWY 28; ARPT AUTHORITIES SHOULD HAVE PLOWED AND SANDED THE RWY AND TAXIWAYS BEFORE AN ACFT SLID OFF THE RWY; NOT AFTER. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING. BRAKING ACTION ON THE FIRST HALF OF THE RWY WAS NORMAL. NO SNOW REMOVAL OR SANDING HAD BEEN DONE ON THE LAST HALF; THIS INFO NOT GIVEN. LOCAL FSDO REQUESTED A WRITTEN REPORT. ACFT WAS NOT DAMAGED OTHER THAN MUD AROUND THE LNDG GEAR. FLOWN OUT THE NEXT DAY. MGR TOOK NO ACTION AND THE CASE HAS BEEN DROPPED. WAS CONCERNED THE TWR HAD NOT MONITORED THE ROLLOUT AND WAS NOT AWARE OF THEIR POSITION ON THE FIELD.