Expert: Capt Paul - 11/1/2006

Question
OK... I think were getting close to what I want and I have one more question.  First, consider were at "true north and disregard any magnetic interference or the variation aspect.  If you are over at that dot you suggested you put on the paper and if London lay under the imaginary line you designated as "e", and you flew down that line looking down at your HSI wouldn't it indicate 180 degrees?  That's what has me confused... it simply seems to me that any heading away from true north would be 190. (Thaks for taking the time to work through this.)
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Thanks, but that doesn't answer the question.  Pick a destination, whereever it is and disregarding magnetic variation, let's dela with geographic issues, what heading would you fly?  I'm not familar with "grid patterns" but when your A350 leaves the geographic pole using your grid system going to anywhere, say, London, wouldn't your heading be 180?
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If I am over the geographic north pole what heading would I fly to get to Seattle?  Or Toronto, or anywhere?

Seems to me the minute you leave the pole your heading for anywhere and forget the magnetic aspect, will by 180 degrees.  

What am I missing here?  That can't be right...

WBD


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If your over either the geographic north pole, or the magnetic north pole, you would be flying what we call "Grid Tracks".  Simplistically, it's a track based navigation, opposed to heading based system.

Because the magnetic poles and geographic poles are located in different places, the magnetic compass becomes somewhat useless in the far northern regions.

But, your magnetic heading would be a little more accurate when flying from the magnetic north pole, which is located somewhere around northern greenland.  However, it does move slightly eash year.

Hope this helps.

Cheers
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Unless you have some navigation knowledge, this is not going to be easy to understand.   The reality is, that near the magnetic north pole, a basic compass will simply spin around until you travel far enough away from the areas of magnetic disturbance, that it is no longer greatly affected.
However, if those disturbance areas didn’t exist, you would only show a south heading (180) if you were in fact heading south.

To simplify this, do the following.  On a sheet of paper draw a cross.  In the center of the cross, mark a spot called “NP.”  You guessed it, North Pole.  On the top of the cross put an “N”, and on the right and “E”, then “S” and “W” as appropriate.

So long as you are not exactly on the “NP” mark, you will have some form of bearing from the “NP” (North Pole), regardless of the direction of travel, and at any different points the bearings will be different.

This is grid navigation in its simplest form.    Now, because of the areas of magnetic disturbance, “Grid” is the only accurate form of navigation in this area.  But!  This is exactly how the compass would work in this area, if it were NOT for the areas of magnetic disturbance.
The following may help you to understand.

There are three North’s commonly in use in the world:
Grid North: the direction of a grid line which is parallel to the central meridian on the National Grid.
True North: the direction of a meridian of longitude which converges on the North Pole.

Magnetic North: the direction indicated by a magnetic compass. Magnetic North moves slowly with a variable rate and currently is west of Grid North.

Differences
The horizontal angular difference between True North and Magnetic North is called MAGNETIC VARIATION or DECLINATION. The horizontal angular difference between Grid North and Magnetic North is called GRID MAGNETIC ANGLE. It is this angle which needs to be applied when converting between magnetic and grid bearings.

I hope this helps.

Cheers


Answer
No problem with taking the time to answer this.  I admit, it's a difficult subject to fully understand.


First, let's take the magnetic issue out of the question, and deal with these simply as true tracks (Headings).  Thus assuming that the "N" indication on a compass, always points to the North Pole (Geographic).


Now, if you were exactly at the North Pole (and we assume the aforementioned to be correct) then every destination FROM the North Pole would in fact have a southerly RELATIVE BEARING.  


Before I go further, let’s understand a few things about Bearings.

Bearing — the horizontal direction from one terrestrial point to another; basically synonymous with azimuth.


Bearing, however, may be expressed in several ways:


1.   “True Bearing” and “Magnetic Bearing” are the angular directions in degrees measured clockwise from true north and magnetic north, respectively;

2.   “Compass Bearing” is expressed in terms of compass points; and

3.   “Relative Bearing” is the angular distance measured clockwise from the heading of a craft (in aviation, relative bearing is often referred to a clock face, that is, “3 o'clock” equals a relative bearing of 90°, etc.).



Now, consider the North Pole as a CENTRE of a compass circle with 360 lines extending outward around it.  In THIS example the northerly line would continue around the earth, and connect with the Southerly line AT the SOUTH POLE.  Do the same with EAST and WEST until they connect.


Now, we are back to the basic idea of the paper diagram that I discussed earlier.  


The short of it is this.  If we are talking about relative bearings, you’re thought of every destination being SOUTH of the North Pole is correct, RELATIVE to the North Pole. In short, from the position of the North Pole, traveling to any other place AWAY from the North Pole, would put the "N" indication in the "Six O'clock position (Not exacly true, but remember, for this example we took magnetic issues out of the question).


However, in reality we are talking of true bearings and magnetic bearings, which in this example we can use synonymously.


Are we getting closer to a mutual understanding?


Let me know if this answers it.  If necessary, I can email some diagrams.


Cheers