Understanding magnetic variation (MagVar)

You are asked to enter your airport's magnetic variation in the project settings dialog (FILE\ PROJECT settings...\ LOCATION tab). It should only be entered when you add VOR and ILS navigation systems to your project.

As a matter of fact, the geographical (true) and the magnetic North are located at different places on the globe. The heading you read on a compass only tells you where the magnetic North is. There is a discrepancy between the true and magnetic North and it varies from place to place. The magnetic variation is the angle you would have to add to a true heading in order to get the magnetic one.

The scenery's coordinate system is adjusted to the true north. In other words, GroundMaker's Y grid axis intersects with the North pole. This also applies to runways, where you enter true headings (imagine a runway with a 0° heading; the centerline, if long enough, would intersect with the North pole). Unfortunately, most runway heading information you find on the internet, in FS or on maps will give you magnetic headings... If you use these values for runway headings in GroundMaker, you will soon realize that runways have different headings when FS. The only way to solve the problem is to find out magnetic variation and do a little bit of math.

Finding out magnetic variation

The following steps will show how to find out magnetic variation (MagVar) and how to calculate true headings for runways.

• Open GroundMaker

Create a new project; enter the latitude and longitude of your scenery's location. Don't forget to enter the altitude. It is very important to enter the correct location of your new scenery project since MagVar varies from place to place. Add a runway on the map and set its heading to 0. Save the project and compile it (read the GroundMaker help to find out how to compile and install FS scenery).

• Run Flight Simulator

Activate the scenery and go to its location. Go into SLEW mode (press Y) and move to the runway's end (use numeric keypad or arrows) as shown in the figure above. Move to the runway's center and turn until it's end is exactly at the center of the screen. Enable the "V" (VIEWS\ VIEW options... menu item) for better accuracy.

Enable the info in the top left corner by pressing SHIFT+Z (cycle until you get heading info as shown above). Write down the HEADING value. The heading shown here is the magnetic one. As you will notice, it does not equal 0 (we set the runway heading to 0°). Finding out the magnetic variation is fairly easy. If the value lies between 0° and 179°, it is the magnetic variation. On the other hand, if it lies between 180° and 359°, you must subtract 360 from it. The result should be negative. Here is an example:

value read: 357° MagVar = 357 - 360 = -3°

 

What to do with the MagVar

If you only know magnetic headings for runways, use the MagVar to find out the true headings required by the GroundMaker runway tool. Simply subtract the MagVar from the magnetic heading you know. Example:

Don't forget that headings must lie in the range of 0° to 359°. In case the result is negative, add 360 to it:

If the result is greater than 359°, subtract 360 from it:

Of course, it never hurts to enter MagVar in the project settings (FILE\ PROJECT settings... menu item). Note that it is only used for the VOR and ILS navigation systems you add to your scenery project.

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(c) 2001-2003 Vincent Koch