PLT OF A BEECH SUPER KING AIR 350 USED GPS NAV TO LOCATE THE OM WHICH WAS OTS FOR THE ILS APCH EVEN THOUGH ATC ADVISED THAT THE APCH WAS NOT AUTH.

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ON JUL/XA/99; I WAS SCHEDULED TO FLY TO NORTH BEND; OR; AT XX30. CURRENT CONDITIONS WERE 300 FT CEILINGS AND 3/4 MI VISIBILITY IN FOG. THE APCH I NEEDED FOR THE CONDITIONS WAS THE ILS 4 IAP AT NORTH BEND. AN FDC NOTAM HAD BEEN ISSUED DENYING USE OF THE ILS APCH PROC BECAUSE THE EMIRE LOM WAS TAKEN OTS FOR MAINT. MY IMMEDIATE SUPVR TOLD ME THAT I COULD STILL FLY THE APCH BY SUBSTITUTING GPS FOR THE LOM. AFTER REFERRING TO FAA ADVISORY CIRCULAR 90-94; I AGREED AND FLEW TO NORTH BEND. THOUGH ZSE DID NOT AGREE THAT FLYING THE ILS WAS AUTH; I WAS CLRED FOR APCH AT NORTH BEND AND FLEW AN UNEVENTFUL ILS. THE NEXT DAY I CONTACTED OUR LCL FSDO; ZSE; AND AN AIRWAYS SPECIALIST TO CLARIFY THE FAA'S POS ON GPS SUBSTITUTION FOR INOP NAVAIDS. UNFORTUNATELY; I GOT DIFFERING OPINIONS ON THE SUBJECT. THOUGH I FEEL MY ACTIONS WERE SAFE AND LEGAL PURSUANT TO FAA ADVISORY CIRCULAR 90-94; I HAVE DECIDED TO FILE THIS RPT. I HOPE THIS RPT WILL LEAD TO CLARIFICATION ON GPS SUBSTITUTION FOR INOP NAVAIDS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: IT WAS DISCUSSED WITH THE RPTR THAT THE APCH WAS NOT LEGAL DUE TO THE FACT THAT REGARDLESS OF SUBSTITUTIONS FOR THE OM; IT IS NOT LEGAL SINCE IT WAS NOT ALLOWED PER FAR PART 97 APCH CHART AND ATC. RPTR AGREES WITH THIS CLARIFICATION AND DECLARES THAT HE IS NOT GOING TO CONDUCT SUCH OPS IN THE FUTURE.