MU300 ACFT LNDG ON ICY RWY RAN OFF END OF RWY DUE TO NIL BRAKING.

Narrative

WE WERE REPOSITIONING FROM BEDFORD; MA; TO LEBANON; NH; PART 91 TO TRANSPORT A STABLE PATIENT TO ATLANTA AS PART 135 AIR AMBULANCE. THE CAPT FLEW THE FULL APCH FOR THE ILS RWY 18 AT LEB. ONBOARD THE ACFT WERE MYSELF; THE CAPT; AND 3 MEDICS (PART OF THE CREW). A NORMAL LNDG WAS MADE. THE ATIS RPTED BRAKING CONDITIONS FAIR TO POOR DUE TO ICE AND SNOW. THE RWY HAD BEEN USED BY OTHER ACFT THAT MORNING WITH NO PROB. UPON LNDG; THE CAPT APPLIED BRAKES AND THE ACFT DECELERATED WELL. WITHIN THE LAST 1000 FT OF RWY; WE ENCOUNTERED SOLID CLR ICE AND BRAKING ACTION BECAME NIL. AT THIS POINT WE WERE AT A SAFE TAXI SPD; BUT COULD NOT SLOW ENOUGH TO MAKE THE 90 DEG TURN OFF THE RWY. SO WE CONTINUED STRAIGHT AND PROCEEDED ABOUT 30 FT BEYOND THE RWY ONTO A GRASS OVERRUN (COVERED WITH ABOUT 4 INCHES OF SNOW). ALL SYS WERE SHUT DOWN. THERE WAS NO DAMAGE TO THE ACFT AND THERE WERE NO INJURIES. THE ACFT WAS THEN TUGGED BACK TO THE FBO. THIS EVENT EXEMPLIFIES THE IMPORTANCE OF ASSESSING WINTER CONDITIONS AND ACFT PERFORMANCE IN THOSE CONDITIONS AND HOW IT MAY AFFECT THE SAFETY OF THE FLT. IT ALSO SHOWS THE IMPORTANCE OF HAVING ACCURATE BRAKING CONDITION RPTS WHEN THOSE CONDITIONS EXIST. IT WAS GOOD TO HEAR THAT THE ARPT PLANS TO LENGTHEN THE RWY WHEN IT GETS WARMER.