FO OF A LR25 SLID OFF THE END OF THE RWY AFTER LOSING CTL DUE TO AN ICY SNOW COVERED PORTION OF THE RWY. A NORMAL LNDG WAS MADE WITH FULL REVERSE THRUST TO THE ACFT TO APPROX 60 KTS WITH BRAKING AND THEN CTL WAS LOST AT APPROX 25 KTS ON ICE. BRAKING ACTION THEN BECAME INEFFECTIVE.

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THE CONDITION OF THE RWY AT TELLURIDE WAS RPTED POOR TO NIL. WE CONTACTED FLT SVC AND OTHER ACFT THAT HAD LANDED -- THEY RPTED THE RWY BEING OK. WE DISCUSSED THE TYPE OF LNDG WE WOULD DO BEFORE WE LANDED. WE WOULD BE USING MINIMAL BRAKING AND REVERSE IDLE. WE ELECTED TO LET THE ACFT ROLL OUT DUE TO PATCHY SNOW AND ICE. THE RWY WAS ICY AND SLIPPERY DUE TO THE SNOW MELTING. WE APPLIED LIGHT BRAKES; BUT NOTHING HAPPENED. WE CONTINUED BRAKING UNTIL WE ENDED UP IN THE OVERRUN WHICH WAS UNPLOWED SNOW. WE WERE ABLE TO TURN THE PLANE AROUND. THERE WAS NO DAMAGE TO AIRPLANE. AFTER THINKING ABOUT THE EVENTS THAT LED UP TO THE SIT; THE ONLY CORRECTIVE ACTION I BELIEVE WOULD CORRECT ANOTHER OCCURRENCE LIKE THIS ONE WOULD BE BETTER DECISION MAKING. ANY TIME YOU HEAR BRAKING ACTION NIL; YOU SHOULD ELECT TO LAND AT ANOTHER ARPT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE WAS OPERATING A LEAR 25 AND THAT THE FO WAS FLYING THE ACFT AT THE TIME OF THE LNDG AND LOSS OF CTL. HE CLARIFIED THAT FULL REVERSE HAD BEEN INITIALLY USED DURING THE LNDG WITH NORMAL BRAKING ACTION PRIOR TO SLOWING SUFFICIENTLY TO COME OUT OF REVERSE AND ROLLING ON TO ICY RWY CONDITIONS. THEIR SPD HAD DISSIPATED TO APPROX 25 KTS WHEN THE BRAKES WERE NOT EFFECTIVE. REVERSE THRUST WAS NOT REINTRODUCED TO HELP STOP THE SLIDING ACFT. AS FAR AS THE RPTR KNOWS; THIS INCIDENT WAS NOT EVER RPTED TO THE FAA. THEREFORE; THERE HAS BEEN NO KNOWN FAA INVESTIGATION OR FOLLOW-UP TO THIS INCIDENT.