ACR LANDS WITH CLRNC ON RWY NOT VISIBLE FROM THE TWR.

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APCHING COS DURING DSCNT AND TALKING TO APCH CTL; WE WERE INFORMED THAT WE WOULD BE VECTORED FOR A VISUAL APCH RWY 17R. ATIS DID NOT MENTION THAT RWY 17L WAS CLOSED AND/OR THAT THE RWY 17L LOC AND GS WAS OTS; SO WE QUESTIONED APCH CTL WHY WE COULDN'T USE RWY 17L. SHE SAID WE COULD; BUT THAT SINCE COS HAD A TEMPORARY TWR AND COULD NOT SEE ALL OF RWY 17L; WE COULD SHOOT THE APCH; BUT THAT THE LNDG 'WAS AT OUR OWN RISK' (HER STATEMENT). AFTER DISCUSSING WITH THE CREW THE SAFETY BENEFITS OF HAVING A GS; LOC; LONGER RWY; BETTER RWY LIGHTING ALL IN HILLY TERRAIN; WE FELT THE 'RISK' WAS ACCEPTABLE AND INFORMED ATC THAT WE WOULD PREFER RWY 17L FOR APCH AND LNDG. WE RECEIVED VECTORS FOR THE APCH TO RWY 17L AND WHEN APCH CTL HANDED US OFF TO COS TWR; WE WERE TOLD WE COULD USE RWY 17L BUT SINCE HE COULD NOT SEE ITS ENTIRE LENGTH; IT WOULD BE AT 'OUR OWN RISK.' I QUESTIONED TWR IF HE WOULD LIKE ME TO CALL COS UNICOM AND HE SAID THERE WAS NO NEED SINCE THERE WAS NO TFC IN THE AREA. OUR LNDG WAS UNEVENTFUL AND WE RPTED CLR OF THE RWY TO TWR WHO THEN CLRED US TO OUR GATE.