Narrative:

We received approach clearance from ZLC and were advised that the initial approach fix (barstow) and NDB were OTS. We were able to fix (banstow) by the published transition route form the sheridan VOR. We therefore elected to use the ILS autoplt coupled approach. The autoplt coupled normally and both navigation receivers agreed throughout the approach. Upon reaching decision height, visibility was such that I was able to determine was were not in the right location and we executed a missed approach. I was familiar with sheridan and was confident that something was wrong with the ILS, so elected to try the VOR DME approach the second time. Conditions were such that we were unable to land from the MDA of this approach, and we requested to return back to our home base of billings. Upon leaving, we communicated our suspicions of the ILS with sheridan FSS, and they said they would call maintenance and have them check it out. We returned to sheridan in about 2 hours. The WX had improved to clear conditions. We therefore flew out to the OM of the ILS and coupled the autoplt again. This time everything worked normally. After landing I went to FSS and asked about the outcome of our former incident. I was informed that maintenance had checked and found the G/south low. Airport maintenance was contacted, and after removing snow around the ILS antenna, the problem was corrected. It would seem appropriate that priority is given to snow removal effecting navigation, rather than to do just the runways and ramps. FSS indicated that the snow removal from the antenna is rather low on the airports priority list. The sheridan ILS OM was notamed OTS during all of this however there is a published DME fix for the OM, which was what we used to determine its location.

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Original NASA ASRS Text

Title: PLT OF SMT ON COUPLED APCH TO SHR BROKE OUT, BUT DID NOT RECOGNIZE AREA, MADE MISSED APCH. ILS ANTENNA POSSIBLY COVERED WITH SNOW CAUSED LOW APCH. WHEN SNOW CLEARED AWAY, ILS WAS NORMAL.

Narrative: WE RECEIVED APCH CLRNC FROM ZLC AND WERE ADVISED THAT THE INITIAL APCH FIX (BARSTOW) AND NDB WERE OTS. WE WERE ABLE TO FIX (BANSTOW) BY THE PUBLISHED TRANSITION ROUTE FORM THE SHERIDAN VOR. WE THEREFORE ELECTED TO USE THE ILS AUTOPLT COUPLED APCH. THE AUTOPLT COUPLED NORMALLY AND BOTH NAV RECEIVERS AGREED THROUGHOUT THE APCH. UPON REACHING DECISION HEIGHT, VISIBILITY WAS SUCH THAT I WAS ABLE TO DETERMINE WAS WERE NOT IN THE RIGHT LOCATION AND WE EXECUTED A MISSED APCH. I WAS FAMILIAR WITH SHERIDAN AND WAS CONFIDENT THAT SOMETHING WAS WRONG WITH THE ILS, SO ELECTED TO TRY THE VOR DME APCH THE SECOND TIME. CONDITIONS WERE SUCH THAT WE WERE UNABLE TO LAND FROM THE MDA OF THIS APCH, AND WE REQUESTED TO RETURN BACK TO OUR HOME BASE OF BILLINGS. UPON LEAVING, WE COMMUNICATED OUR SUSPICIONS OF THE ILS WITH SHERIDAN FSS, AND THEY SAID THEY WOULD CALL MAINT AND HAVE THEM CHK IT OUT. WE RETURNED TO SHERIDAN IN ABOUT 2 HRS. THE WX HAD IMPROVED TO CLR CONDITIONS. WE THEREFORE FLEW OUT TO THE OM OF THE ILS AND COUPLED THE AUTOPLT AGAIN. THIS TIME EVERYTHING WORKED NORMALLY. AFTER LNDG I WENT TO FSS AND ASKED ABOUT THE OUTCOME OF OUR FORMER INCIDENT. I WAS INFORMED THAT MAINT HAD CHKED AND FOUND THE G/S LOW. ARPT MAINT WAS CONTACTED, AND AFTER REMOVING SNOW AROUND THE ILS ANTENNA, THE PROB WAS CORRECTED. IT WOULD SEEM APPROPRIATE THAT PRIORITY IS GIVEN TO SNOW REMOVAL EFFECTING NAV, RATHER THAN TO DO JUST THE RWYS AND RAMPS. FSS INDICATED THAT THE SNOW REMOVAL FROM THE ANTENNA IS RATHER LOW ON THE ARPTS PRIORITY LIST. THE SHERIDAN ILS OM WAS NOTAMED OTS DURING ALL OF THIS HOWEVER THERE IS A PUBLISHED DME FIX FOR THE OM, WHICH WAS WHAT WE USED TO DETERMINE ITS LOCATION.

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.