5 ms·

What is the advantage though? True North is of course easier to understand and use when navigating manually, but what's the benefit in a commercial airliner?

KineticLensman 5y ago
TFA doesn't precisely enumerate them but two I saw were: * removes the ongoing process / cost of updating mag tracks as the Earth's magnetic field shifts * avoids errors that occur when the true/mag difference is correctly specified
maxerickson 5y ago
It removes the need to maintain the lookup tables that are used to compute magnetic north from the true north determined by the navigation system. I don't know anything about them, but looking it up, apparently inertial navigation systems can determine true north by sensing the spin axis of the planet! So it isn't just a 'gps is easier' kind of thing.
andylynch 5y ago
There are two main ones 1. modern navigation systems often work in true North already but have to map to magnetic for display & to match charts. 2. magnetic north moves! This greatly complicates how you deal with the first point. I don’t envy the Canadian pilots they were talking about who tested some of this current stuff, and found their plane’s idea of the runway direction way very different from where it lay.
dan_hawkins 5y ago
First Air Flight 6560 crash [0] [0] https://en.wikipedia.org/wiki/First_Air_Flight_6560 https://en.wikipedia.org/wiki/First_Air_Flight_6560
- dan_hawkins 5y ago
  PS: I highly recommend crash analysis written by Admiral Cloudberg. In the above case: [0] Arctic Approach: The crash of First Air flight 6560 [0] https://admiralcloudberg.medium.com/arctic-approach-the-crash-of-first-air-flight-6560-8949c8716ea9 https://admiralcloudberg.medium.com/arctic-approach-the-cras...
redis_mlc 5y ago
> What is the advantage though? Canada needs to move off magnetic north because the magnetic north pole is located in Canada, and it's changing rapidly. But that doesn't apply to the US. Sounds like a terrible idea for the training aircraft fleet to force them to buy INS systems when they all have magnetic compasses.
JumpCrisscross 5y ago
> What is the advantage From the article: “The migration of the geographic magnetic poles has accelerated in recent years, adding to the relentless task of updating systems and distributing the associated flight information. The AHRTAG points out that updating aircraft declination look-up tables is a specialist and expensive maintenance activity that has no effect on the way an aircraft derives its directional information. It merely ensures the result is displayed as a magnetic value that is normally less accurate than the originally determined True heading. And, if a future variation shift is sufficient to affect airport assets – like runway and taxiway signage and markings, plus instrument procedures, landing aids documentation, and FMS coding – at a major hub, the cost can top $20-30 million.” https://www.flightglobal.com/flight-international/why-aviations-compass-is-shifting-towards-true-navigation/145663.article https://www.flightglobal.com/flight-international/why-aviati...
- Grustaf 5y ago
  That last paragraph makes sense, changing taxi markings etc is inherently expensive. The lookup tables part is harder to understand, but perhaps the airplane software is very badly written.
rkangel 5y ago
It's a fundamental principle thing, that has some knock-on practical effects. Navigation is fundamentally getting from point A to point B. To do that, you steer a course between the two. Do you want to describe the angle of that course in reference to (a) A fixed line that never moves, such that the angle ('bearing') of that course is always the same (b) A line that moves around, seemingly randomly, particularly if you are near one of the poles of our planet Obviously from first principles, you'd pick the first. Due to historical navigation technology it was more convenient to use the second though. We had an instrument (magnetic compass) that would directly give us reference for (b), and so we described everything in those terms, and maintained tables of offsets so that we could calculate (a). Using (b) - magnetic North - causes some problems and because very few aircraft, and no commercial ones, rely on magnetic bearings as a primary source of navigation those problems are not worth it. One of the problems comes when you start labelling things that are fixed relative to (a), because they're attached to the ground but you label them using (b). After a few years the labelling is wrong and they need relabelling. This requires everything from pointing of radio beacons to repainting runways. It's all needed for effectively historical reasons. There are two Norths: The one that points in a constant direction on the Earth's surface. Getting from point A to point B on the Earth is fundamentally what navigation is and so having a fixed reference for that is good (modulo continental drift). The direction that a magnetic compass points. This is at an arbitrary and changing offset to any direction on the Earth's surface. Why
- flavius29663 5y ago
  Now I get it, using the magnetic north is akin to the daylight saving time kerfuffle, on steroids - you basically have to account for variations even during the same flight if you fly near the poles.
  - Grustaf 5y ago
    The magnetic north is even affected by local phenomena, at least when you're on the ground, so it's worse than that.
- ryandrake 5y ago
  > (a) A fixed line that never moves, such that the angle ('bearing') of that course is always the same Just to nit-pick your otherwise great comment: This may be true for short, general aviation navigation, but long haul airliners typically navigate via great circle routes, which do change true course throughout the route.

KineticLensman 5y ago

TFA doesn't precisely enumerate them but two I saw were: * removes the ongoing process / cost of updating mag tracks as the Earth's magnetic field shifts * avoids errors that occur when the true/mag difference is correctly specified

maxerickson 5y ago

It removes the need to maintain the lookup tables that are used to compute magnetic north from the true north determined by the navigation system. I don't know anything about them, but looking it up, apparently inertial navigation systems can determine true north by sensing the spin axis of the planet! So it isn't just a 'gps is easier' kind of thing.

andylynch 5y ago

There are two main ones 1. modern navigation systems often work in true North already but have to map to magnetic for display & to match charts. 2. magnetic north moves! This greatly complicates how you deal with the first point. I don’t envy the Canadian pilots they were talking about who tested some of this current stuff, and found their plane’s idea of the runway direction way very different from where it lay.

dan_hawkins 5y ago

First Air Flight 6560 crash [0] [0] https://en.wikipedia.org/wiki/First_Air_Flight_6560 https://en.wikipedia.org/wiki/First_Air_Flight_6560

dan_hawkins 5y ago
PS: I highly recommend crash analysis written by Admiral Cloudberg. In the above case: [0] Arctic Approach: The crash of First Air flight 6560 [0] https://admiralcloudberg.medium.com/arctic-approach-the-crash-of-first-air-flight-6560-8949c8716ea9 https://admiralcloudberg.medium.com/arctic-approach-the-cras...

redis_mlc 5y ago

> What is the advantage though? Canada needs to move off magnetic north because the magnetic north pole is located in Canada, and it's changing rapidly. But that doesn't apply to the US. Sounds like a terrible idea for the training aircraft fleet to force them to buy INS systems when they all have magnetic compasses.

JumpCrisscross 5y ago

> What is the advantage From the article: “The migration of the geographic magnetic poles has accelerated in recent years, adding to the relentless task of updating systems and distributing the associated flight information. The AHRTAG points out that updating aircraft declination look-up tables is a specialist and expensive maintenance activity that has no effect on the way an aircraft derives its directional information. It merely ensures the result is displayed as a magnetic value that is normally less accurate than the originally determined True heading. And, if a future variation shift is sufficient to affect airport assets – like runway and taxiway signage and markings, plus instrument procedures, landing aids documentation, and FMS coding – at a major hub, the cost can top $20-30 million.” https://www.flightglobal.com/flight-international/why-aviations-compass-is-shifting-towards-true-navigation/145663.article https://www.flightglobal.com/flight-international/why-aviati...

Grustaf 5y ago
That last paragraph makes sense, changing taxi markings etc is inherently expensive. The lookup tables part is harder to understand, but perhaps the airplane software is very badly written.

rkangel 5y ago

It's a fundamental principle thing, that has some knock-on practical effects. Navigation is fundamentally getting from point A to point B. To do that, you steer a course between the two. Do you want to describe the angle of that course in reference to (a) A fixed line that never moves, such that the angle ('bearing') of that course is always the same (b) A line that moves around, seemingly randomly, particularly if you are near one of the poles of our planet Obviously from first principles, you'd pick the first. Due to historical navigation technology it was more convenient to use the second though. We had an instrument (magnetic compass) that would directly give us reference for (b), and so we described everything in those terms, and maintained tables of offsets so that we could calculate (a). Using (b) - magnetic North - causes some problems and because very few aircraft, and no commercial ones, rely on magnetic bearings as a primary source of navigation those problems are not worth it. One of the problems comes when you start labelling things that are fixed relative to (a), because they're attached to the ground but you label them using (b). After a few years the labelling is wrong and they need relabelling. This requires everything from pointing of radio beacons to repainting runways. It's all needed for effectively historical reasons. There are two Norths: The one that points in a constant direction on the Earth's surface. Getting from point A to point B on the Earth is fundamentally what navigation is and so having a fixed reference for that is good (modulo continental drift). The direction that a magnetic compass points. This is at an arbitrary and changing offset to any direction on the Earth's surface. Why

flavius29663 5y ago
Now I get it, using the magnetic north is akin to the daylight saving time kerfuffle, on steroids - you basically have to account for variations even during the same flight if you fly near the poles.
- Grustaf 5y ago
  The magnetic north is even affected by local phenomena, at least when you're on the ground, so it's worse than that.
ryandrake 5y ago
> (a) A fixed line that never moves, such that the angle ('bearing') of that course is always the same Just to nit-pick your otherwise great comment: This may be true for short, general aviation navigation, but long haul airliners typically navigate via great circle routes, which do change true course throughout the route.