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Magnetic Variation east is - and west is + but what if true course is 0 or 180 degree


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I am not sure about the rest of the world, but almost every approach plate and airport diagram I've seen , as well as all the maps made in North America, show you the variation between true and magneting North. I am really only familiar with west coast maps (used to do a lot of orienteering), but from what I recall, the MV is to the East here (I am currently in OR). So True course 000°, Mag course is going to be about 345° to go the exact same way, or to the same place.

Or do I have it bass-ackwards? I need more coffee...

Does this help?



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Sgt, USMC, 10 years proud service, Inactive reserve now :D

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So here is the question if I fly towards true course 0 or 180 degree than do I add the MV or do I subtract the MV


Magnetic variation is totally independant of the aircraft heading .


If you do a google search of "Magnetic Variation maps" you will find maps that have the magnetic variation Isogonal lines marked on them , an isogonal is a line that has a common MAGVAR , they look (almost) like the Isobar pressure weather maps.


Aviation charts have the Isogonal lines shown on them complete with the magnetic variation applicable to that line.

The local magnetic variation is then applied to either ;

(1) the aircraft's current true heading.


(2) the true track of a flight plan line during flight planning.


In our flight simulator there exists a MAGVAR (magnetic variation) variable that can be applied to true tracks or headings.

In other words the sim knows the local Magnetic variation for the current part of the world that your aircraft is flying in.

The magnetic variation is applied where applicable in the instrument code by the instrument developer.




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From the old "sexist" days of my Navy flight training:


"True Virgins Make Dull Company - ADD - Wine"


Going from True heading through Variation, compensate for instrument Deviation to Mag heading, ADD Western variation (subtract east variation).


Going the other way -


"Can Dead Men Vote Twice At Elections" -


Compass correct for Deviation results in Magnetic heading, Variation results in True heading - add EAST variation (subtract west variation).


Always worked for me!

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If the question is actually about magnetic variation, as it seems to me, then that is, as Karol indicates, a function of location, not of your course. So the Denver area is currently 9º E while the 0º line runs through Columbia, MO. This is true whether you're headed north, south, east, west or somewhere in between.


But if it's what altitude to fly on a specific course, as mikeandpatty indicate, then true course is immaterial, as the heading is referenced to magnetic north.


However, the magvar in FSX is that from around the year 2005, so Denver is closer to 11º E and the 0º line is closer to Chicago (closer, because I don't have the exact figures from back then). This is because the magnetic variation (the difference between true and magnetic north) is constantly changing. It even affects the labeling of runways, after a number of years, since the runway number is the mag heading to the nearest 10º with the trailing zero lopped off.


Larry N.

As Skylab would say:

Remember: Aviation is NOT an exact Science!

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So here is the question if I fly towards true course 0 or 180 degree than do I add the MV or do I subtract the MV


You're mixing apples and oranges. Perhaps you're thinking about ATC and traffic separation headings which are from 0-179 degrees (east) and 180 to 359 degrees (west).

Don't be confused by the EAST and WEST explanation in most navigational manuals, which I think is very confusing as well in the long way that they explain it always seems to be. It's seems to be all about the orientation of the explainer. :) Is he moving or traveling or is he standing in one spot and pointing a compass?


East and west of what? It's NOT from where zero degrees longitude (the Prime Meridian) where time also starts and ends, nor does it have anything to do with the IDL (International Date Line) which is at 180 degrees longitude.


East and west in navigation in regards to magnetic variation is east and west of the Magnetic (Agonic line), which is 0 degrees MV)......and, as Larry explained here, is constantly changing.


I don't know why navigational manuals always get into the east and west explanation, and by the time you're finished reading it you're more confused than when you started. :)


The simple answer to your question is this:


If your location is +MV you would ADD that amount to your MAGNETIC heading to travel (fly) a TRUE heading.


The opposite holds true with -MV as then you would SUBTRACT that amount from your MAGNETIC heading to travel (fly) a TRUE heading.





To fly TRUE NORTH (0 degrees) and the MV is 10 degrees simply turn to right to a Mag. heading of 10 degrees.

To fly TRUE NORTH (0 degrees) and the MV is -10 degrees simply turn to left to a Mag. heading of 350 degrees.


Don't get confused about any direction you're flying. Just think of the compass rose as 0 to 360 degrees and add to or subtract the MV to acquire at TH or TC (true course in some manuals).


It doesn't matter where in the world or what direction you're heading as long as you know the +/- MV value.


As also explained here by others, navigation in FS as well as in the Real World aviation such as ATC assigned headings, VOR radials, runways, ILS approaches, etc. all directions and headings are given to us as magnetic headings; however when you're reading a map as example or flying using the sextant, knowing MV becomes important.


It's just that simple.




Now to confuse everyone I've added an example of sextant navigation. :)



The lines on the graph represent Latitude and Longitude and the orientation of the graph is just as if it were a map.

The center dot on the sextant graph is N57° 45' W133° 40'...as entered in this screen shot.

Where the Blue and Red lines cross is the aircraft's location in respect to the center of the graph.

The azimuth of the last star read was 180 degrees as seen below "STAR"

If I want to head 180° TRUE SOUTH my magnetic heading will be 152.4° (notice the MV is 27.6 degrees)


Don'' let the positive value here confuse you.

It's merely written that way to satisfy MSFS coding as written in the Beaumont/Bitzer Sextant for FS which references MV as 0 to 360 degrees.....

Any value on the sextant from 0 to 179 is a negative MV and you would subtract that value to fly a TH

Any value from 180 to 360 is actually positive MV and would be the difference of the value and 360 degrees.

So a -10° MV in the FS sextant as written as 10 degrees MV in the Beaumont/Bitzer Bubble sextant for FS

And a +10° MV in the FS sextant shows up as a MV of 350 degrees and to fly a TH heading would be plus 10 degrees.


When flying and using the sextant I always think of it as 360-10=350 (a minus is a plus and and plus is a minus) so I would turn left to acquire a (heading correction) from magnetic to true. :confused:


Yes, that can be confusing!:confused:...but just ignore it for the answer to your question. :)


BTW numbers entered in the sextant for celestial navigation are for West and South are negative numbers and North and East are Positive numbers..... so by looking at the value in the sextant I'm somewhere in the northwest of the intersection of the Prime Meridian and Equator. Those are the values you would enter in the sextant after figuring out where you are....in relationship to the star you're reading found here.. http://aa.usno.navy.mil/data/docs/celnavtable.php


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