CPR SMT ALT DEVIATION EXCURSION FROM CLRNC ALT.

Narrative

I DEPARTED CASPER; WYOMING; ON AN IFR FLT; SINGLE PLT TO HAYDEN; CO. ROUTING OF CASPER DIRECT CHEROKEE VOR V-26 TO CELIA INTXN DIRECT HAYDEN. APPROX 50 NM S OF CHEROKEE VOR ON V-26; I ASKED FOR A LOWER ALT. I WAS EVENTUALLY CLRED TO 12000' FOR FL200. IN THE DSCNT I WAS TOLD THAT THE HAYDEN ARPT WAS CLOSED. I ASKED CENTER FOR A VECTOR TO INTERCEPT THE LOC FOR THE ILS RWY 10 INTO HAYDEN BECAUSE HAYDEN UNICOM SAID THERE WAS NO PROB WITH THE ARPT OR THE RWY AND THERE WAS NO APPARENT REASON FOR THE ARPT TO BE CLOSED. HAYDEN UNICOM SAID THEY WOULD TRY TO CONTACT THE ARPT MGR AND TRY TO HAVE IT OPENED SO I COULD LAND. CENTER THEN CLRED ME ON A VECTOR TO INTERCEPT THE LOC FOR THE ILS (DME) 10 AT HAYDEN. I BROKE OUT INTO VFR CONDITIONS AS I INTERCEPTED THE LOC. AS I PROCEEDED INBND ON THE LOC I ASSUMED THAT I HAD BEEN CLRED FOR THE APCH TO HAYDEN. AT 15 NM DME ON THE IHDN LOC I STARTED OUT OF 12000' FOR 9000' WHICH IS APPROVED ON THE APCH PLATE. CENTER THEN CAME BACK AFTER RPTING OUT OF 12000' FOR 9000' AND SAID I WAS NOT CLRED FOR AN APCH TO HAYDEN AND TO MAINTAIN 12000' AND HOLD AT THE CHE VOR BECAUSE THE ARPT WAS CLOSED. I WAS ALREADY OUT OF 11000' AND DSNDING FAST. I THEN CANCELLED IFR AND PROCEEDED VFR TO THE HAYDEN ARPT AND CIRCLED THE ARPT WAITING FOR IT TO OPEN. THIS INCIDENT COULD HAVE BEEN PREVENTED IF I HAD VERIFIED CLRNC; LISTENED MORE CLOSELY TO CENTER; AND FOLLOWED ATC INSTRUCTIONS TO THE LETTER AND NOT ASSUMED I WAS CLRED FOR MORE THAN I WAS.