Long Range Heading Differences
Thread Starter
Joined: Nov 2007
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From: NYC
Long Range Heading Differences
Hello,
I noticed if you have a long leg, especially of a few hundred miles, the heading at the beginning of the leg and at the end of the leg differ by a few degrees. I'm thinking the difference is due to Magnetic Variation and the curvature of the Earth. Are there any other factors?
Thanks.
I noticed if you have a long leg, especially of a few hundred miles, the heading at the beginning of the leg and at the end of the leg differ by a few degrees. I'm thinking the difference is due to Magnetic Variation and the curvature of the Earth. Are there any other factors?
Thanks.
Joined: Jul 1999
Posts: 444
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From: England
In the flat Earth society, the heading would indeed remain constant. However, when I was last up high enough the horizon definitely looked curved. If you can get the kit to navigate a rhumb line the heading would also remain constant, but most systems use great circle nav.
Joined: Jan 2008
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From: Reading, UK
I noticed if you have a long leg, especially of a few hundred miles, the heading at the beginning of the leg and at the end of the leg differ by a few degrees. I'm thinking the difference is due to Magnetic Variation and the curvature of the Earth. Are there any other factors?
Joined: Sep 2016
Posts: 937
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From: USA
Great circle navigation in a nutshell:
Imagine you're flying from one point of the equator to the opposite side of the equator, over the North Pole. In the straightest path possible. First your true course will be 360, then, as you cross the pole, it will flip and be 180 for the second half of the trip.
Now imagine a similar flight where you pass kinda near the pole, but not directly over it. Your true course will start out something like 020, then as you pass near the pole quickly change to the south, (even though you're still flying a straight line, it is crossing each meridian at a different angle). Finishing the trip at 160.
A trip between pretty much any 2 points on the planet, is a less extreme example of the same thing, and the course angle relative to the meridians will always be changing.
Imagine you're flying from one point of the equator to the opposite side of the equator, over the North Pole. In the straightest path possible. First your true course will be 360, then, as you cross the pole, it will flip and be 180 for the second half of the trip.
Now imagine a similar flight where you pass kinda near the pole, but not directly over it. Your true course will start out something like 020, then as you pass near the pole quickly change to the south, (even though you're still flying a straight line, it is crossing each meridian at a different angle). Finishing the trip at 160.
A trip between pretty much any 2 points on the planet, is a less extreme example of the same thing, and the course angle relative to the meridians will always be changing.
Last edited by Vessbot; 30th September 2022 at 12:46.
Joined: Jun 2002
Aviation Qualifications: PPL
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From: east ESSEX
Suggest you use Google Earth;use the little info box,top left ,press view,then press `grid`,and all the latitudes/longitudes should appear;next box is `tools. select `ruler`.
Now pick a point ,say anywhere in California,and draw a line around the World to London(England).It should go across Canada,Greenland to England in a curve/Great circle.Note it will also give you your initial heading,approx 035 *.Now draw another line from about 1/3 of the track ,(HudsonsBay area) parallel to the main track to the East coast of Greenland.IT should be about 056* appx. at the start of that line.Now draw the final track ,parallel to the main track to London.the initial heading will be about 097*.So ,you have travelled about 110* of Longitude,and the heading has changed about 60*....
If you travel E OR W around the Equator,your heading will not change(much)...
Now pick a point ,say anywhere in California,and draw a line around the World to London(England).It should go across Canada,Greenland to England in a curve/Great circle.Note it will also give you your initial heading,approx 035 *.Now draw another line from about 1/3 of the track ,(HudsonsBay area) parallel to the main track to the East coast of Greenland.IT should be about 056* appx. at the start of that line.Now draw the final track ,parallel to the main track to London.the initial heading will be about 097*.So ,you have travelled about 110* of Longitude,and the heading has changed about 60*....
If you travel E OR W around the Equator,your heading will not change(much)...
Joined: Jan 2009
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From: Cab of a Freight Train
Hello,
I noticed if you have a long leg, especially of a few hundred miles, the heading at the beginning of the leg and at the end of the leg differ by a few degrees. I'm thinking the difference is due to Magnetic Variation and the curvature of the Earth. Are there any other factors?
Thanks.
I noticed if you have a long leg, especially of a few hundred miles, the heading at the beginning of the leg and at the end of the leg differ by a few degrees. I'm thinking the difference is due to Magnetic Variation and the curvature of the Earth. Are there any other factors?
Thanks.
Joined: Jul 2020
Posts: 12
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From: Around latitude 0
That’s pretty much what you said, both Meriden convergence & FMC VAR tables are involved. Bill bulfer B737 NG FMC USER’s GUIDE talks briefly about in a section entitled DIR TO, it’s a brief review on the matter.
Joined: Dec 2005
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From: Wellington,NZ
This is nav 101.
You don't need to be a ATPL holder to know the answer - this sort of knowledge will be the routine province of PPL and above. The type of study and application to do with it tends to mean it's not forgotten, whether over 12 years or 20. (Or in my case, 40.)
You don't need to be a ATPL holder to know the answer - this sort of knowledge will be the routine province of PPL and above. The type of study and application to do with it tends to mean it's not forgotten, whether over 12 years or 20. (Or in my case, 40.)
Fleet Manager
Joined: Apr 2001
Aviation Qualifications: ATPL
Posts: 7,448
Likes: 310
From: various places .....
Folks. I think all and sundry are well aware that I don't get excited too much about a bit of argy bargy. However, this thread has gone off the rails both significantly and rapidly.
The OP asked a question. Whether that question be good, bad, or indifferent is not a consideration. Please, either answer the question, as asked, or hold your peace and just shake your head, if necessary.
While we are quite happy with a bit of to and fro and humour, we really prefer to keep things on a pleasant and reasonably polite even keel.
The OP, perhaps reasonably, got a bit hot under the collar and was more than a bit out of order in his/her responses so a short period on the bench to think about things looks to be in order.
Above all, folks, let's play the ball and not the player.
Here endeth the lesson and homily.
The OP asked a question. Whether that question be good, bad, or indifferent is not a consideration. Please, either answer the question, as asked, or hold your peace and just shake your head, if necessary.
While we are quite happy with a bit of to and fro and humour, we really prefer to keep things on a pleasant and reasonably polite even keel.
The OP, perhaps reasonably, got a bit hot under the collar and was more than a bit out of order in his/her responses so a short period on the bench to think about things looks to be in order.
Above all, folks, let's play the ball and not the player.
Here endeth the lesson and homily.
Joined: Nov 1999
Aviation Qualifications: ATPL
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From: UK
Fair enough. I apologise for mine, (now deleted). But I question whether it is reasonable to have to spend time researching a poster's history - especially if they claim ATPL, then ask a basic ATPL navigation question.
My reaction came from genuine concern that an unqualified pilot might have been on the line.
My reaction came from genuine concern that an unqualified pilot might have been on the line.
Fleet Manager
Joined: Apr 2001
Aviation Qualifications: ATPL
Posts: 7,448
Likes: 310
From: various places .....
Guys,
It's a difficult path one treads in moderation. My personal aim is to stay out of sight on the sidelines and let folks have their say. Every now and again, though, shirt collars start to get a tad sweaty and folks arc up a little when a calming coffee might have been the better strategy. Just part of the tapestry of life which, fortunately, doesn't cause us too much problem in this forum.
Keep in mind, also, that after problem posts are deleted, often there are others to tidy up where those others become irrelevant after the problems are removed. Not that there is any concern with the latter, just an editorial tidy up exercise.
It's a difficult path one treads in moderation. My personal aim is to stay out of sight on the sidelines and let folks have their say. Every now and again, though, shirt collars start to get a tad sweaty and folks arc up a little when a calming coffee might have been the better strategy. Just part of the tapestry of life which, fortunately, doesn't cause us too much problem in this forum.
Keep in mind, also, that after problem posts are deleted, often there are others to tidy up where those others become irrelevant after the problems are removed. Not that there is any concern with the latter, just an editorial tidy up exercise.
Joined: Dec 2005
Posts: 1,694
Likes: 15
From: Wellington,NZ
Guys,
It's a difficult path one treads in moderation. My personal aim is to stay out of sight on the sidelines and let folks have their say. Every now and again, though, shirt collars start to get a tad sweaty and folks arc up a little when a calming coffee might have been the better strategy. Just part of the tapestry of life which, fortunately, doesn't cause us too much problem in this forum.
Keep in mind, also, that after problem posts are deleted, often there are others to tidy up where those others become irrelevant after the problems are removed. Not that there is any concern with the latter, just an editorial tidy up exercise.
It's a difficult path one treads in moderation. My personal aim is to stay out of sight on the sidelines and let folks have their say. Every now and again, though, shirt collars start to get a tad sweaty and folks arc up a little when a calming coffee might have been the better strategy. Just part of the tapestry of life which, fortunately, doesn't cause us too much problem in this forum.
Keep in mind, also, that after problem posts are deleted, often there are others to tidy up where those others become irrelevant after the problems are removed. Not that there is any concern with the latter, just an editorial tidy up exercise.