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I imagine checking ILS accuracy by measuring ILS signals at various points along the approach path is routine maintenance, although I don't know how it is done. How often must this kind of check be done to ensure the ILS is still accurate enough?

Tanner Swett
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Manu H
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    Related: https://aviation.stackexchange.com/questions/35341/what-is-flight-inspection-as-provided-by-cobham-aviation-services/ – 60levelchange Feb 02 '20 at 14:14
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    I don't know the exact answer (hence why this is just a comment) but from experience the ILS is monitored continuously, checked by a vehicle driving down the runway weekly and calibrated (by using an aircraft) twice yearly. – 60levelchange Feb 02 '20 at 14:15
  • I think there is a difference between inspection and monitoring. Your use of the word “checked” may be too ambiguous. – Dean F. Feb 02 '20 at 14:33

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The FAA has a Flight Inspection Manual which describes the checks that must be done and how often. Table 4.1 shows that an ILS must be flight checked every 540 days. Section 15 describes what happens during one of these checks. It's quite an extensive inspection!

Dave-CFII
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  • Note that many countries (at least in Europe) seem to be working with a 180 day interval for ILS calibration. – 60levelchange Feb 02 '20 at 14:31
  • @J. Hougaard - Are there any specifics on routine monitoring? – Dean F. Feb 02 '20 at 14:34
  • @DeanF. Been digging around a bit, doesn't seem like the ICAO provides that many specific intervals (although they do describe quite extensively what exactly has to be done - see DOC 8071). So it would seem it is largely up to member states to determine how often calibration is needed. As for monitoring alone, that is done continuously – 60levelchange Feb 02 '20 at 14:37
  • Considering that monitoring and inspecting are different, can one of you define or give the parameters, techniques, or tasks/items/steps to accomplish for monitoring? – Dean F. Feb 02 '20 at 14:53
  • @DeanF. The equipment and radio beams are monitored with physical equipment on the airfield. I am not an electrical engineer, don't ask me ho exactly it works – 60levelchange Feb 02 '20 at 14:56
  • There's some discussion of navaid monitoring in JO 7210: https://tfmlearning.faa.gov/Publications/atpubs/FAC/0305.html – Dave-CFII Feb 02 '20 at 15:18
  • @J.Hougaard Given their announcements for 2019, the German ATC checks the ILS in FRA quite often (several times a year). – PerlDuck Feb 02 '20 at 17:12
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    @PerlDuck They probably don't do all runways at the same time, hence the large number of announcements – 60levelchange Feb 02 '20 at 17:48
  • Each ILS gets test flown as well. – mongo Feb 04 '20 at 15:24
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    @J.Hougaard When possible / needed all runways are done in one go. Individual runways then are done after adjustments to the ILS system or modifications to the direct environment (to assess impact of possible signal reflection interference). Some runways in Frankfurt have dual ILS installations with two different glide slopes (3.00° & 3.20°), so there is quite a lot to calibrate. – DeltaLima Feb 04 '20 at 16:05