The Earth's magnetic poles are constantly shifting, resulting in a significant distance between the true and magnetic poles. This means that while using them as references for heading at lower latitudes makes sense, using them as such while flying in polar regions causes often unacceptable inaccuracy.

In a simulator, I noticed that many modern airliners have a toggle to switch between referencing true and magnetic north as appropriate; but at what distance from a pole would this toggle be activated?

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    $\begingroup$ Whilst the north magnetic pole does shift it is a slow process, and not the reason for using true north at the poles. The reason is that close to the poles the compass will try to point at the ground instead of moving freely. $\endgroup$ – Ben Dec 1 '17 at 2:42
  • $\begingroup$ I hadn't considered that. Good point! $\endgroup$ – Jules Dec 1 '17 at 2:44

In Boeing aircraft the default is to select MAG. When the aircraft enters the polar region it will auto switch to TRU. The pilot can also select TRU when outside the polar region.

The polar region is defined as north of 82 deg N latitude or south of 82 deg S latitude. It also includes the region north of 70 deg N between 80 deg W longitude and 130 deg W longitude and the region south of 60 deg S between 120 deg E and 160 deg E longitude.

Polar Regions, B777 FOM

  • $\begingroup$ What is the reason for the additional areas below the 82°? $\endgroup$ – Czechnology Dec 4 '17 at 23:06
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    $\begingroup$ @Czechnology Those are the areas around the magnetic poles. Near them magnetic compasses (and heading) are pretty much useless. $\endgroup$ – Gerry Dec 5 '17 at 0:17

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