Magnetic Variation Incorrectly Displayed

Hi all

First of all - I think Navigraph Charts is a fantastic tool and had huge improvements lately. I use JeppFD for IFR flying IRL and wish it had even half the features Navigraph has…

I recently raised a point in the Navigraph discord and was advised to bring it up in the forums, and that was that magnetic variation (MV) is incorrectly displayed in the Navigraph app.

When clicking or searching for a waypoint, Navigraph Charts (at least, the desktop app) shows you the magnetic variation. This magnetic variation is incredibly handy for users who may want to copy or mimic radar vectors that are being given to an aircraft for a pilot intercept on an ILS, as self vectoring yourself can be difficult. The data on Flightradar24 shows a True track, so to translate this to a radar vector one must account for MV (and also wind).

The problem in Navigraph Charts is that it shows the MV as a stand-alone degree value and does not provide whether or not the MV is east of west. The saying “East is Least and West is Best” applies to translating True to Magnetic HDGs/TRKs. This means, if we want to correct for “xx°E” we would have to take our track MINUS (“East is Least”) the MV.

Although this may not pose much of an issue for some users, if you wanted to mimic radar vectors onto the ILS at YSSY Sydney, for instance (where the ILS/IVA is only given from radar vectors) you may choose to quickly click on a nearby waypoint to check the MV so you can get the vector right whilst observing your aircraft on the moving map, see below:

We can see here, that the MV is shown as “12.9°” but it doesn’t specify whether it is E or W, so you could easily make the mistake of adding 13° to a TRK instead of subtracting it - which leaves a potential 26° variation. If we compare this to what is shown on the AD chart, for instance:

At the end of the day, whether or not you personally find use in the MV being shown, it is something that can both be handy in the sim and is used very frequently IRL (from personal experience), and if you’re going to display it at all, you may as well display it correctly - because showing the MV without an E or W label is a little bit like a shopping cart with a dodgy wheel, you probably don’t care less, until you go to use it.

Kind Regards,

Ben Long

Hi Ben! Thank you for the feedback.

In Navigraph Charts, the magnetic variation is written as a positive or negative number, representing east and west respectively! In this particular case, you can see that the variation is 12.9° (positive) and the chart shows 13°E. This way, all you have to do is subtract the visible number from the TRK and you should get the correct value!

Would perhaps switching it around help? So that it would say -12.9 in this case? Or would you prefer to show E/W as well?

Kind Regards,

Thanks for your help!

Interesting and I’ve only just picked up on that difference. I’ve never seen MV differentiated like this (where West is a negative value) but that doesn’t mean its wrong. Out of interest, is it a case of mathematical logic or is it a standard used in a particular country? On (all that I’m familiar with) AD charts as well as enroute/terminal and also VFR charts MV is displayed as an E/W value.

Food for thought really! I’m sure you guys have a lot you’re working on.

Kind regards,

Ben Long

Hi Ben,

The positive/negative E/W sign for magnetic variation (declination) is an international convention
even if charts display it as a more friendly E/W value, as you pointed out.
WMM and IGRF software calculations of MV use this convention
Interestingly, MS has, in the past, adopted an inverse convention (W being positive) in its internal file coding (BGL files) that has persisted since then



1 Like

Some great insight there @hervesors ! Thank you for providing great sources.
As you mentioned, this is a convention that is also used by us both internally and for the navigation data that we provide to our 3rd parties, depending on the format!

We could add E/W to the interface too! It should be easy enough. Would that be helpful?

Kind Regards,

I concur, some interesting insight @hervesors and I was unfamiliar with this convention until now!

It is important to point out, however, that when used in the context on air navigation, you will always take reference from North, so in an aviation context, you will almost always see these values given as E/W. Again, the mathematical conventions behind this may trump the need to have this implemented - I’m not expert on that. I have been trained in VFR and IFR navigation, and translating True to Magnetic using an E/W value is taught to become second nature.

If I can give my 2 cents, the E/W convention for MV will always be the primary for aviation because in practicality, it is a problem of navigation, not mathematics. But don’t tell CASA, EASA, FAA, etc this - they will happily disagree :smiley:

Yes it would be helpful, but as has been pointed out, I was wrong to give the impression it was incorrect. Overall, in an aviation context, E/W would simply make more sense.

Kind regards,

Ben Long