Narrative:

We were operating into sav after tower closure, in and out of light turbulence and heavy rain and had been cleared for the ILS. While maneuvering for the approach, our clearance was changed to ILS runway 9 GS inoperative with the explanation that the GS was unreliable after tower closure because of taxiing aircraft. We completed the approach and the next morning I noticed the note (in fine print) in the profile section of the commercial plates which states GS unreliable after tower closure due to taxiing aircraft interfering with the GS. Although center corrected their error and prevented us from making the same error, there remains several questions: 1) why was the GS transmitter and/or the taxiway installed to allow this interference and what is being done to do away with this problem? 2) if one were to inadvertently fly an ILS approach and if a taxiing aircraft were to interfere with the signal of the GS, would there not be adequate indication in the cockpit so that proper action could be taken? If the answer to this question is yes, then why not allow the full ILS approach? If the answer is no, are we safe on any ILS approach?

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Original NASA ASRS Text

Title: CAPT OF ACR LGT ACFT QUESTIONS ATC CLRNC FOR ILS APCH WHEN THE GS MAY BE UNRELIABLE.

Narrative: WE WERE OPERATING INTO SAV AFTER TWR CLOSURE, IN AND OUT OF LIGHT TURB AND HVY RAIN AND HAD BEEN CLRED FOR THE ILS. WHILE MANEUVERING FOR THE APCH, OUR CLRNC WAS CHANGED TO ILS RWY 9 GS INOP WITH THE EXPLANATION THAT THE GS WAS UNRELIABLE AFTER TWR CLOSURE BECAUSE OF TAXIING ACFT. WE COMPLETED THE APCH AND THE NEXT MORNING I NOTICED THE NOTE (IN FINE PRINT) IN THE PROFILE SECTION OF THE COMMERCIAL PLATES WHICH STATES GS UNRELIABLE AFTER TWR CLOSURE DUE TO TAXIING ACFT INTERFERING WITH THE GS. ALTHOUGH CTR CORRECTED THEIR ERROR AND PREVENTED US FROM MAKING THE SAME ERROR, THERE REMAINS SEVERAL QUESTIONS: 1) WHY WAS THE GS XMITTER AND/OR THE TAXIWAY INSTALLED TO ALLOW THIS INTERFERENCE AND WHAT IS BEING DONE TO DO AWAY WITH THIS PROBLEM? 2) IF ONE WERE TO INADVERTENTLY FLY AN ILS APCH AND IF A TAXIING ACFT WERE TO INTERFERE WITH THE SIGNAL OF THE GS, WOULD THERE NOT BE ADEQUATE INDICATION IN THE COCKPIT SO THAT PROPER ACTION COULD BE TAKEN? IF THE ANSWER TO THIS QUESTION IS YES, THEN WHY NOT ALLOW THE FULL ILS APCH? IF THE ANSWER IS NO, ARE WE SAFE ON ANY ILS APCH?

Data retrieved from NASA's ASRS site as of July 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.