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Aerial navigation is designed to primarily use magnetic headings. Consider an international flight which flies a great circle route across the North Pole, or an aerial tour around the Atlantic area. What should the pilots do to avoid getting lost?

This question asks about VOR alignment, and this question discusses the coordinate system used; but neither discuss what the pilots should do in the cockpit. How do you align the HSI? And what happens if GPS has malfunctioned?

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  • $\begingroup$ No international flights cross the poles. $\endgroup$ – Simon Feb 27 '16 at 13:52
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    $\begingroup$ @Simon Some flights fly close to the north magnetic pole though, though not the true pole. $\endgroup$ – SMS von der Tann Feb 27 '16 at 14:13
  • $\begingroup$ @SMSvonderTann Can you provide an example? The closest I can find is about 60 miles away. $\endgroup$ – Simon Feb 27 '16 at 14:30
  • $\begingroup$ See also “No aircraft crosses directly over the pole” - Why? $\endgroup$ – ChrisW Feb 27 '16 at 15:44
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    $\begingroup$ The flight would be in a Special Areas of Operation, under Class II Navigation because of an Area of Magnetic Unreliability (AMU). To be confirmed by someone better informed: In SIMS - Order 8900.1 it seems GPS and Inertial are required per table 3-111 Special Authorization Information Table—Long-Range Navigation Systems in vol. 3, ch. 29, sect. 8 - § 3-2443 (entries 2 and 3). $\endgroup$ – mins Feb 28 '16 at 12:36
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You raise an interesting question, and I assume you refer to flying near the poles using a lightly equipped general aviation aircraft. Airliners or jets usually have inertial navigation equipment that is working autonomously and will not be affected by pole proximity.

Several procedures could be taken in a general aviation aircraft to improve situational awareness:

  • You need indeed to deslave the HSI from the magnetic slaving transmitter in order to use it as a directional gyro manually slaved (see How does a horizontal situation indicator (HSI) work?). The directional gyro will have to be realigned manually regularly to compensate for precession (astronomical precession is 15°/hour at the pole, to the right at North pole, to the left at South pole).
  • Don't forget it is still possible to use astronomical navigation if you are in VFR conditions and able to see stars (at night) or the Sun (during day). This will not be very accurate but a precision better than 5 to 10 degrees could be reached without needing a sextant. Computing your location only from star positions is a complex operation, but it is rather easy to find out aircraft true heading thanks to the Sun or major stars relative position from aircraft nose. You could use this heading to manually realign your unslaved HSI/directional gyro.
  • Regarding GPS, it is strongly advised to check in advance GPS coverage near the pole using RAIM prediction function, either from the onboard GPS or using web servers. This will allow you to check the coverage should be assured according GPS satellite locations relative to your position (an outage is always possible). When flying in such remote locations I always bring with me a portable standalone GPS unit, in addition to panel mounted GPS.
  • Standard navigation (keeping track of position thanks to heading and clock) of course should be used and near coasts you could cross-check your computed position using landmarks, but above ice caps you will have few or no landmarks.
  • If you are lucky enough to have an inertial navigation platform on board, your position will be kept rather accurately independently of any other input, with an error of the order of 10 NM after 7 hours of flight.

The main issue you will encounter in a general aviation aircraft flying near the pole is their endurance is often limited, regulatory fuel reserves are higher than usual, airports are few and far apart, alternates may close quickly due to quickly changing weather conditions. This means that when you fly or are ferrying an aircraft in those regions, you could definitely not afford to get lost or not to be sure of your position.

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    $\begingroup$ What is the minimum equipment required to fly in a polar region and in an area of magnetic unreliability? From your answer it seems there is none. Is a VFR flight allowed? $\endgroup$ – mins Mar 3 '16 at 12:23

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