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Driver170

MAG difference on ILS app

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I only fly to payware airports and i've noticed that on my charts at LPPT rwy 03 FAT is 027* but in my FMS its showing 026* but after i set both courses to 027 per my charts after the localizer has been tracked and captured, my courses then change to 025*? This happens at all airports and if i can remember also happened to default fsx airports.

 

Is this to do with software that calculates MAG VAR ? Thats why you get the difference? I know in the RW plogs pilots can ignore tracks that are different on the flightplan compared to whats showing in the legs page of the FMS.

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Is this to do with software that calculates MAG VAR ? Thats why you get the difference?

 

The mag data in the sim was put into the sim when the original FSX was created over a decade ago. This changes over time (you can see it on just about any airport diagram - http://155.178.201.160/d-tpp/1502/00320AD.PDF - where it will list an annual rate of change by the true north pointer).

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Ignore the mag difference unless it's significant (significant as in when you say 'that's odd').  Focus on what you know, for example the LOC "beam" is about 3 deg wide and it is generally aligned with the runway extended center line.  This is physical reality, the beam is lined up with the runway and that doesn't move no matter what the magnetic poles do; in other words, the magnetic headings are only approximately the true heading. As a convention, the magnetic declination is provided on charts with a year and annual change.  You can use that information to determine if the difference is significant.

 

As far as the autopilot that is actually tracking the LOC beam is concerned, there is only one beam regardless of the course or heading.  The main reason we set the course is so the APPR display is heading up.  There are some other issues involved but the point is a localizer is not like a VOR with 360 radials, there is only one localizer.  I almost forgot to mention that the FAA allows a +/- 6 deg error in the VOR/LOC display, unlike simulation where there is no error and no error is very unrealistic.

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Vernon,

It is probably due to the default MagVar data in FSX being out of sync with the AIRAC data. When you set the course manually and then select the 'ILS approach' in the arrivals page of the FMS, it resets the CRS to whats in the AIRAC cycle (not sure why it is setting it to 25° though).

I believe if you select a 'NON ILS approach' you can tune the CRS manually (and still do an ILS approach), the CRS will stay as you set it (haven't done this myself for a while as I normally always use ILS).


Regards
Ian
 

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So is this something that can't be fixed then?

The NGX fixes it. PMDG Setup>Options>Simulation>Set FSX LOC CRS>ON. You don't need to concern yourself with it. If the option is on, it's all automactic.

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I got back today and checked my settings and i have got fsx loc crs on? so how come i get the difference in course between the MCP and the FMC ?


2015-2-28_17-33-26-219.png


025 on the MCP and 026 on the FMC which you can't really see

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so how come i get the difference in course between the MCP and the FMC ?
It is explained on page 72 of the Introduction manual  under SET FSX LOC CRS.

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Well its not matching it for some reason!

Vernon

 

I don't know what else to say. Maybe the cats on prune can explain the deal to where it makes sense.

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Vernon

 

Did a test flight with the NGX at payware LPPT airport (Aerosoft), ILS rwy03 and the MCP shows 026, same as FMC. I have AIRAC 1501 with  magvar.bgl  of 2010 from http://www.aero.sors.fr/navaids.html

Then, same here, what else can I say? It makes no sense why your MCP shows 025.

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Easy, please don't worry about those minor deviations in mag headings/bearings/courses.  One degree, that is always explainable but not worth the time and effort to figure out.  I am using the 2015 bgl with no problem.

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I was using the 2010 bgl for two years. Then in 2012 I made some hardware changes and reinstalled FSX but never reinstalled 2010 nor have I installed 2015 bgl so I am flying in 2005-2006 FSX data. The NGX can handle it.

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Do you still find differences in courses during ILS app?

Yes. With the 2010 installed at KTPA on ILS 01 I would set the course knob to 007 and when the localizer was captured the course would change to 006. Right now with 2010 or 2015 not installed most of the ILS approaches result in a course change when the localizer is captured.

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I've currently got 2015 installed so going to check a few airports for the change!

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