VOR Orientation

T

turbojet28

Well-Known Member
Hello,

I was just planning a flight and I have one quick question. I've read that VORs are oriented to magnetic north, therefore when using a VOR, I thought, you would have to put your magnetic course on the OBS (you would track the radial/course TO/FROM the VOR that corresponds to your magnetic course, in other words). Is this correct? It seems that some VORs are oriented differently than others, even though they are fairly close together. When I look at the course line I drew on my sectional, it hits the compass rose of the VOR on a course that is 4-5 degrees off of my magnetic course (almost seems like it is always my true course which is reflected on the compass rose). This is what prompted me to ask this question. Should I turn my OBS to the course TO/FROM the VOR that my line hits the compass rose on, or did I make errors when calculating my mag. course and should just turn my mag. course into the OBS? (man that was a mouthful!
smile.gif
) Thanks!

-turbojet28
 
Mag. varation changes depending on where you are, that's probably why your courses are a bit off, take a look at the isogonic lines (dashed magenta lines). How far apart are your VORs?
 
Thanks Ed. I had checked the isogonic lines before and my course goes right accross the 5ºW one. Obviously, I added 5 to my true course to get my mag course and it was still a few degrees off. It is probably just my error in calculating true course! Thanks again.
 
Remember that the magnetic poles drift constantly, and the VORs are not constantly updated to keep up with the drift. Consequently, the VORs do not always (and in fact generally will not) exactly match up with the magnetic headings. But they should be close. There is a threshold of change where the FAA will go back and "retune" the VOR, but I don't remember what that is. It's probably listed in the AIM somewhere.

MF
 
VOR stations are oriented to magnetic north.

I see you're up in Michigan. Notice how close you lines of variation are on the sectional (changes from 6 to 7 degrees in about 50nn). That's because you are close to the magnetic north pole. Hence, your VOR stations will probably be pointed differently as you go east and west.

Look at the Los Angeles sectional. You have to travel quite far to get any change in variation.
 
[ QUOTE ]
Remember that the magnetic poles drift constantly, and the VORs are not constantly updated to keep up with the drift. Consequently, the VORs do not always (and in fact generally will not) exactly match up with the magnetic headings. But they should be close. There is a threshold of change where the FAA will go back and "retune" the VOR, but I don't remember what that is. It's probably listed in the AIM somewhere.

MF

[/ QUOTE ]
Hit the nail on the head right there! I think I remember reading that they don't even fix the magnetic variation of the VORs on a routine basis; it's only adjusted when the VOR goes down for maitenance and even then it's only a maybe that they'll fix it. Of course, I could be wrong, but I know they don't adjust the variation very often.
 
This is so commonly misunderstood. VORs are NOT necessarily alligned with magnetic north. Looking at two ends of a short airway segment will reveal this instantly. A straight line that does not have recip courses? Look in the AFD and you will see each VOR has its own variation. This tells you the VOR is alligned off magnetic north by X degrees. Why is this important? Well, many people use the radial as their magnetic course when flight planning and then adjust from there. Of course, commonly the radial is not the magnetic course. In a no-wind condition, flying a 180 radial with a 5 deg variation and and East wind, you would be drifting off course and wondering why that darn needle is moving? Must be the compass, right? Well, maybe
shocked.gif
 
Yes indeedy! Which is why my 5 T's actually have 6; "Track" coming right after "Twist".

(I also use a 7th T, "Think", but I digress.)
 
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