FO QUESTIONED WHETHER IT WAS LEGAL TO START A DSCNT TO THE APCH DME ARC ALT UNTIL ESTABLISHED ON THE ARC AFTER BEING CLRED FOR THE APCH BY ATC WHILE ON AN AIRWAY WITH THE SAME MINIMUM ENRTE ALT.

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ON OR ABOUT JUN/XX/93 I WAS OPERATING AS FO FOR FLT FROM GCC (GILLETTE; WY) TO SHR (SHERIDAN; WY). WE WERE OPERATING IN IMC CONDITIONS AT A FINAL ASSIGNED ALT OF 10000 FT MSL; INBOUND ON V586 TO SHR VORTAC. ZDV CTLR HAD IDENTED US IN RADAR CONTACT AND TRANSFERRED US TO ZLC ON 127.75 ABOUT 35 DME FROM SHR. HE DID NOT IDENT US IN RADAR CONTACT AND REQUESTED OUR DME DISTANCE FROM SHR VORTAC AND VERIFY LEVEL AT 10000 FT. WE IMMEDIATELY NOTED THE CTLR SEEMED ANNOYED. AT 30 DME FROM SHR VORTAC; WE HAD TO BREAK INTO THE CTLR'S COMS TO OTHER ACFT TO REQUEST CLRNC FOR THE ILS/DME RWY 31 APCH. THIS APCH INVOLVES INTERCEPTING THE 20 DME ARC FROM SHR VORTAC AND THE CTLR WAS NOT GOING TO GIVE US ADEQUATE TIME TO INTERCEPT THE ARC AT OUR 250 KT GND SPD. THE CTLR; AGAIN SEEMING ANNOYED; CLRED US FOR THE APCH; BUT GAVE NO AMENDED ALT INSTRUCTIONS. THE CAPT THEN ORDERED A DSCNT TO THE PUBLISHED ARC ALT OF 7000 FT. WE WERE STILL ON V586 AT OUR ASSIGNED ALT OF 10000 FT. I INDICATED THAT I DID NOT THINK WE COULD DSND UNTIL ESTABLISHED ON A PORTION OF THE PUBLISHED APCH (I.E.; THE 20 DME ARC). I ALSO INDICATED THAT I DID NOT THINK WE WERE IN RADAR CONTACT AND THAT HE SHOULD RPT DSNDING (10000 FT IS ABOUT THE LOWER LIMIT OF ZLC RADAR COVERAGE). THROUGH ABOUT 8000 FT; WHILE ON THE ARC; THE ZLC CTLR SEEMED PANICKED WHEN HE ASKED FOR OUR POS AND ALT. WE THEN SWITCHED TO FSS/ADVISORY FREQ. THE FSS ATTENDANT TOLD US ZLC WANTED TO KNOW OUR ALT AND POS. THE PROB WITH THIS AREA IS THAT RADAR COVERAGE VARIES WITH HOW CLOSE YOU ARE TO THE BIG HORN MOUNTAINS. ZLC WILL ALSO CLR YOU FOR THE APCH FROM A CRUISE ALT WITHOUT ANY FURTHER ALT INSTRUCTIONS LEAVING YOU TO DSND TO APCH ALT ON A RATHER SHORT ARC. ALSO; THE NOS CHARTS THAT WE USE DO NOT CLEARLY INDICATE WHETHER THE APCH IS AFFORDED RADAR COVERAGE. THE CTLR SHOULD CLEARLY INDICATE WHETHER DSCNT TO THE MEA IS AUTHORIZED WITH A 'CLRED FOR THE APCH' CLRNC. OTHER PLTS I QUESTIONED DID NOT BELIEVE DSCNT TO THE MINIMUM ENRTE ALT WOULD BE AUTHORIZED BUT WERE NOT CERTAIN.