Localizer heading/magvar precision

While I was working on fixing/patching the offset localizer issue (see Offset localizer) I noticed that with the Navigraph data the heading and/or magvar of the localizer seem to only be accurate to a full degree.

When I patch the localizers to no longer be forced to runway heading (which at the moment is a bug in MSFS that hopefully will be fixed by Asobo in the future), as it also was with FSX or P3D, I see that localizers that are not offset and should be dead center are now slightly at a wrong angle.
Take for example the runway 08R at EDDP. When I patch the forced runway heading bug for that runway and fly an ILS approach I’ll end up in the grass to the right of the runway.

This is the data for this situation:

	Airport: TT:AIRPORTEK.EDDP.name
		Ident: EDDP (21 8E B7 01) @ 114CF8
		Runway: 08R / 26L
			Heading: 85.7005844116211 (B3 66 AB 42) @ 114D58
		Ident: ILSR (A2 A5 28 02) @ 505B8
		Magvar: 357.0 (00 80 B2 43) @ 505B4
			Heading: 82.7005844116211 (B3 66 A5 42) @ 505C8
		Ident: ILSR (A2 A5 28 02) @ 3F140
		Magvar: 357.0 (00 80 B2 43) @ 3F13C
			Heading: 82.0 (00 00 A4 42) @ 3F150
			Width: 5.0 (00 00 A0 40) @ 3F154

The heading in the runway is always the True-Heading (the magvar value on the airport object itself has no influence).

For the localizer to be centered the sum of heading and magvar of the ILS/localizer has to be the same value as the runway heading. As you can see in this example for the stock data it matches (magvar 357.0 = 3° East + 82.7° => 85.7°, the same as the value of the runway heading.

But in the data from Navigraph the value for the localizer heading is only 82.0° with 3.0°E for the magvar, which adds up to 85.0°, 0.7° off the correct value which is enough to miss the runway.

When I edit the file from Navigraph to have a heading of 82.7° or a magvar of 3.7°E (or any combination that the sum gets to the true runway heading of 85.7°) the ILS approach works flawlessly.

I checked multiple localizer angles and it seems the Navigraph data is always slightly of, between 0 and 1°.
For me it looks like the heading and/or magvar values on the ILS/localizer need to have at least a precision of 0.1° for the ILS to be precise enough.

This can also visually be seen in Little Navmap.
ILS from the Navigraph data:

Navigraph data edited to heading 52.7°/magvar 3.0°E:

As I mentioned at the moment this will not be an issue for most users, as it requires to patch the stock files to stop the sim from forcing the localizer to the runway heading no matter the heading from the localizer, but as this is currently breaking deliberate offset localizers it’s hopefully only a matter of time until it is fixed by Asobo for everyone.

I’m also not sure what you can do from your side to have those values more precise.
If the raw nav data you have access to for heading/magvar of the localizer has already a precision of 0.1° that would probably be the easiest thing to just use it so.
And at the moment there is no urgent need because of the bug in MSFS, it’s more of a heads-up for when it will become relevant. But if you already have precise data it could be an easy win.


P.S.: For reference here is the stock file where I patched the forced-heading-bug for EDDP 08R/ILSR, there you can see the behavior in-sim when the heading and magvar of your ILS/localizer data is taken to determine the localizer heading.
eddp_ilsr_patched.zip (854.0 KB)

Hi Jan,
as always, thanks for the details and your help to improve our data. We are working exactly on this solution because we have indeed only integer values. Since a few days, we are finishing with the complete analyzes of the different approaches and how we can fix all. We have now defined the flow and we will start the implementation from tomorrow on.

Due the complexity, I´m not sure, if this fix will be included in the upcoming 2014 but latest with the next cycle in the new year, we can offer a really accurate approach for ALL!! types of approaches (LOC/ILS and offset). So, please be patience - we are working on it.

Thank you,

PS: Merry Christmas, if we don´t read us anymore :christmas_tree:

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Hi Richard,
that’s great news! I’m looking forward to it :slight_smile:

Danke und Frohe Weihnachten,

Hi Jan,
we had finished the implementation of the exact headings for all types of approaches now (including offsets). We will test a little more during the day and if all looks good (what I expect now), we will release a christmas revision 6 …

So, you can expect this changes before the next cycle :wink:

Cheers and a nice evening

PS: currently we use 3 digits after the comma but we can change this very easily to more or less - to have more or less precision

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Hi Jan,
revision 6 is online now … the localizer courses (ILS/Loc and offset) should be correct now and more accurate. Let me know, when you need something more :slight_smile:

AIRAC 2013 revision 6:

Merry Christmas,

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