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ILS Localizer heading

scruffyduck

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There are a number of threads and posts here about the difference between stock localizer heading and the associated runway heading. I have just come across this while adding ILS support to ADE. I have confirmed with Asobo that the runway heading is true (as it always has been) but the localizer heading is now magnetic. Previously it was true. It's not clear why this change was made.

What I know about air navigation and ILS approaches can be written on the head of a pin. I do know that one flies at an angle to the runway to acquire the localizer and then follow it to the runway. I assume therefore that generally the localizer needs to align with the runway. An extreme example of a large magvar is YSSY (-13) so that rwy 07 has a true heading of ~74.079 while the localizer has a heading of ~ 61.079. Flying on ~61.079 does not align the aircraft with the runway unless the instrumentation is adjusted to allow for the magvar?

So how does this get handled? Do we change the localizer heading in the airport data to take account of the magvar. I think there are some ILS not aligned with the runway though.

I would like to get a definitive approach to handling localizer data so that it works correctly for ILS approaches.

All advice and suggestions much appreciated
 

=rk=

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Jon, it is my understanding, which is also carefully constrained on a pin, that the localizer intercepts the glide slope. In two dimensions, this could be seen as a horizontal plane, that is the localizer signal that draws the plane in like a moth from any direction. The glide slope would be an angled "track" that descends through the localizer plane, planes fly under and then into the glide slope to meet it.

That is the end of my smattering of understanding and the rest is pure superstition, but it seems likely that the instrumentation has a range to account for this variance in trajectory, that would make alignment adjustments in both the vertical and horizontal, presuming the plane was able to intersect the glide slope in the first place.
 
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For US airports, the definitive source for information on any specific ILS’s technical parameters is the FAA’s eNASR web site.


You would select “Instrument Landing System” from the menu, and enter the ILS identifier without the leading “I”. It gives a wealth of information about all components of a given ILS. The localizer heading is listed in degrees magnetic.

Unfortunately this only covers ILS systems in the 50 US states and US territories.
 
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Well - my last flip has been a while ago but as far as I remember the Runway heading (the numbers painted on) were magnetic as well. At my homeport they were changing the numbers the other day because the magnetic northpole keeps moving (sob) what actually caused some confusion over the next couple of weeks - was fun thou.....;)
 
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For my latest airports ive been setting the ILS heading to what is mentioned in the AIP and charts. This shows up as the course that is auto-tracked on fms displays (a320, g1000's etc)

Then playing with the magvar for each ILS to position the aircraft on the correct track when in the Sim. On my last project the magvar was stated as 2E, (358 in the Sim) but I believe I ended up with ~1.5E (358.5) to get the correct alignment..

-- Finn

Sent fra min MAR-LX1A via Tapatalk
 
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Well - my last flip has been a while ago but as far as I remember the Runway heading (the numbers painted on) were magnetic as well. At my homeport they were changing the numbers the other day because the magnetic northpole keeps moving (sob) what actually caused some confusion over the next couple of weeks - was fun thou.....;)
You are correct, Runway headings are almost always stated as magnetic headings so you can use a magnetic compass to align your aircraft with the runway, so if the runway heading stated in the approach chart is 242 and your magnetic heading indicator, HSI or whatever shows 242 on approach you should be aligned with the centerline of the runway. What's also correct is that the magnetic field lines change direction over time so sometimes runway headings change, too. Look at Speyer airport in Germany (EDRY) which still has a slightly visible runway marking reading 35 and 27 respectively which has been painted over with 34 / 16 a few years before the runway extension was built. Salzburg airport in Austria (LOWS) also had its runway heading changed a few years ago. The only place where true headings are stated in charts is the northernmost Arctic if I'm not mistaken, for example northern Canada, where the field lines run almost horizontally so the magnetic deviation is absurdly high and changes rapidly so it would not be feasible to use magnetic headings here.
 
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