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](https://aviation.stackexchange.com/questions/351/how-are-vors-oriented-near-the-magnetic-poles) asks about VOR alignment, and [this question](https://aviation.stackexchange.com/questions/17282/is-the-heading-used-near-the-pole) 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?