Magnetic variation exam question

avongil

avongil

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Hi everyone, I am preparing to take the written exam and am having trouble finding the magnetic deviation on a section of a sectional that does not have a magenta dashed line with it stamped on there.
I am using Gleim online test prep. I don't understand where the magnetic deviation is found. The problem says that that it is 6 degrees.

Form the VOR on the sectional (since VOR radials are magnetic and not true) the magnetic deviation seems like it is 2 degrees as measured with the online tools. see image: http://imgur.com/YAZ28sLl.png
 
I found the magenta dashed line all the way in the far south west corner of the sectional. Sneaky FAA.... What I still want to know is why the measured course with the plotter does not coincide with the location of the radials on the VOR. also the magenta line states 6 degrees, but it measures 12.

???

Thanks
 
VOR twist. The VOR shows the magnetic declination when it was aligned, which could easily be several decades ago. The chart shows what the VOR reads, not the current magnetic course, and a twist of 4 deg isn't unusual at all.
 
Terminology alert! Magnetic Deviation and Magnetic Variation (aka Magnetic Declination) are not the same. The magenta lines on the Sectional indicate variation, not deviation.

Deviation is caused by local magnetic sources, usually metal objects or electric currents in your plane. You won't find this on any Sectional.

-Skip
 
Skip Miller said:
Terminology alert! Magnetic Deviation and Magnetic Variation (aka Magnetic Declination) are not the same. The magenta lines on the Sectional indicate variation, not deviation.

Deviation is caused by local magnetic sources, usually metal objects or electric currents in your plane. You won't find this on any Sectional.

-Skip
Click to expand...
This
 
Shouldn't the title of this thread be "Magnetic Variation"? Compasses deviate, at least according to the old mariner's saying "Can Dead Men Vote Twice".

True North minus Variation = Magnetic.
 
avongil said:
Hi everyone, I am preparing to take the written exam and am having trouble finding the magnetic deviation on a section of a sectional that does not have a magenta dashed line with it stamped on there.
I am using Gleim online test prep. I don't understand where the magnetic deviation is found. The problem says that that it is 6 degrees.

Form the VOR on the sectional (since VOR radials are magnetic and not true) the magnetic deviation seems like it is 2 degrees as measured with the online tools. see image: http://imgur.com/YAZ28sLl.png
Click to expand...

First of all, you seem to be talking about variation, not deviation.

Variation is the difference between true north and magnetic north.

Deviation is the error of a particular compass installed in a particular aircraft due to electromagnetic fields and magnetized pieces of metal.

You stated that the sectional chart excerpt does not have a line of magnetic variation--called an isogonic line--on it. You also stated "the problem says that it is 6 degrees" (although it should also say east or west). Well there is your answer. Because it is not shown the chart, the FAA has told you what it is in the question.

If the FAA wanted you to take deviation into account, they will ask for "compass heading" and refer you to a figure which shows an example of a compass deviation correction card.
 
avongil said:
I found the magenta dashed line all the way in the far south west corner of the sectional. Sneaky FAA.... What I still want to know is why the measured course with the plotter does not coincide with the location of the radials on the VOR. also the magenta line states 6 degrees, but it measures 12.

???

Thanks
Click to expand...

FYI the isogonic lines do not point north, they only tell you where the noted variations occur. Don't try to measure the isogonic line angle and think they'll match the variation value.

And as others said, don't confuse variation with deviation.
 
exncsurfer said:
FYI the isogonic lines do not point north, they only tell you where the noted variations occur. Don't try to measure the isogonic line angle and think they'll match the variation value.
Click to expand...
That's correct, though I don't think it's what the OP was referring to. I think he meant that the course as plotted, when referred to magnetic north, doesn't agree with the VOR radials, which has to do with the fact that the VOR radials are referred to station declination (magnetic variation at the VOR station) as measured maybe 30 years ago.

Actually, I'm not sure what he meant by "the magenta line states 6 degrees, but measures 12". Maybe he was assuming that the isogonic lines point toward magnetic north.

Here's a question: are the isogonic lines great circles that terminate at the magnetic north pole?
 
avongil said:
I found the magenta dashed line all the way in the far south west corner of the sectional. Sneaky FAA.... What I still want to know is why the measured course with the plotter does not coincide with the location of the radials on the VOR.
Click to expand...
because the VOR radials are magnetic, the measured course is true

also the magenta line states 6 degrees, but it measures 12.
Click to expand...
converting from magnetic to true, -6 degree variation - 6 degree 'course' of this imaginary line = -12 which is what you measured with your plotter(or whatever).

since the isogonic lines don't point north, don't measure them
 
azure said:
Here's a question: are the isogonic lines great circles that terminate at the magnetic north pole?
Click to expand...


No, they're not. They're not really circles at all. Magnetic variation is influenced by iron in the earth's molten core, and as things move around and continents drift and earthquakes shift things and whatever else, the isogonic lines move around a bit and they form odd shaped swirls.
 
Half Fast said:
No, they're not. They're not really circles at all. Magnetic variation is influenced by iron in the earth's molten core, and as things move around and continents drift and earthquakes shift things and whatever else, the isogonic lines move around a bit and they form odd shaped swirls.
Click to expand...

Here's a picture:

page1-5400px-World_Magnetic_Declination_2015.pdf.jpg
 
Half Fast said:
No, they're not. They're not really circles at all. Magnetic variation is influenced by iron in the earth's molten core, and as things move around and continents drift and earthquakes shift things and whatever else, the isogonic lines move around a bit and they form odd shaped swirls.
Click to expand...
Correct on all points. I was going to post a link to the map that Matthew posted, but he beat me to it; and besides, I've never figured out how to post an image inline on this board.
 
On the test questions, if an isogonic line isn't shown on the sectional, variation will be mentioned in the question itself.
 
write-stuff said:
On the test questions, if an isogonic line isn't shown on the sectional, variation will be mentioned in the question itself.
Click to expand...

Unless, of course, the question is about flying across the Bermuda triangle, in which case variation changes randomly and causes compasses to spin.

:)
 
avongil said:
Hi everyone, I am preparing to take the written exam and am having trouble finding the magnetic deviation on a section of a sectional that does not have a magenta dashed line with it stamped on there.
I am using Gleim online test prep. I don't understand where the magnetic deviation is found. The problem says that that it is 6 degrees.

Form the VOR on the sectional (since VOR radials are magnetic and not true) the magnetic deviation seems like it is 2 degrees as measured with the online tools. see image: http://imgur.com/YAZ28sLl.png
Click to expand...
Which one from the FAA guide? http://www.faa.gov/training_testing/testing/test_questions/media/sport_rec_private_akts.pdf

(Sorry to be a butthead, but using the actual item from the FAA material will help others on this.)
 
azure said:
Correct on all points. I was going to post a link to the map that Matthew posted, but he beat me to it; and besides, I've never figured out how to post an image inline on this board.
Click to expand...

And notice that the south pole is not directly opposite the north pole, but is instead at significantly lower latitude. The SMP isn't even over Antarctica.
 
MAKG1 said:
VOR twist. The VOR shows the magnetic declination when it was aligned, which could easily be several decades ago. The chart shows what the VOR reads, not the current magnetic course, and a twist of 4 deg isn't unusual at all.
Click to expand...
It may NEVER have actually been aligned with magnetic north. It really doesn't matter much as long as the actual declination is known.
 
Thank you, that clears up the multitude of errors I was making.
 
I always found these to be helpful in giving the "big picture".
 

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Here is a follow up so it can help others. They key to finding the variation is to look at the lower left hand corner of the sectional excerpt:
This is the image of the sectional.
https://i.imgur.com/bPDxRvE.jpg

The question was:

Determine the magnetic heading for a flight from Allendale County Airport (area 1) to Claxton-Evans County Airport (area 2). The wind is from 090° at 16 knots and the true airspeed is 90 knots.

a: 230°.
b: 209°.
c: 212°.

---

I am glad I asked here. Got the correct answer super fast and explained everything I did wrong. While I like the Gleim product their answer to my question was not complete and took two days.
 
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