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:
.\Official\OneStore\fs-base\scenery\0601\APX51130.bgl Airport: TT:AIRPORTEK.EDDP.name Ident: EDDP (21 8E B7 01) @ 114CF8 Runway: 08R / 26L Heading: 85.7005844116211 (B3 66 AB 42) @ 114D58 .\Official\OneStore\fs-base-nav\scenery\0601\NAX51130.bgl ILS/VOR: ILS RW08R Ident: ILSR (A2 A5 28 02) @ 505B8 Magvar: 357.0 (00 80 B2 43) @ 505B4 Localizer: Heading: 82.7005844116211 (B3 66 A5 42) @ 505C8 .\Community\navigraph-navdata\scenery\scenery\0601\NAX51130.bgl ILS/VOR: ILS/GS CAT III RW08R Ident: ILSR (A2 A5 28 02) @ 3F140 Magvar: 357.0 (00 80 B2 43) @ 3F13C Localizer: Heading: 82.0 (00 00 A4 42) @ 3F150 Width: 5.0 (00 00 A0 40) @ 3F154
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)