Inspired by a friend’s adventures (in boats and on foot) and by @Timothy ’s north pole flight, I have been thinking about a trip along the north west passage to Alaska, then back via southern Canada or the continental US.
Disappointingly, I found this in the Aspen POH supplement:
The G500 manual says something similar:
If you’re not flying an airbus , does this mean you need a very good free gyro to do polar grid navigation? Can the G1000 do this?
Of course, it would be possible to code something up for the iPad. Would SkyDemon be interested in supporting grid navigation?
What would concern me is that there are places on the earth which are nowhere near 70N or 70S and where the mag variation goes pretty wild. So what does this really mean?
I recall seeing similar limits on the GNS boxes, but nothing actually happens apart from there being no basemap; you can still fly waypoint to waypoint. OTOH an autopilot always flies a heading so if the mag variation is massive, how does that work?
The gyros in the Ipad, or any other consumer device like that, are rubbish for enroute nav by a factor of 100x to 1000×.
There are several old threads here on this stuff e.g. this one but not covering the polar issue.
INS is the only solution but there is no GA product. The cheapest one is about 20k and that’s an uncertified box which you would have to, ahem, velcro 
I wouldn’t worry about grid navigation. It was designed to be used by specialist Navigators sitting in the back of V Bombers with nothing else to do. It is completely unsuited to single pilot operations.
We have an evening together on 19th March. Let’s talk about it then. It is much less scary than the books and manuals would have you believe.
Oh, and Peter, it is easy enough to set a GNS up to use True.
The easiest way to set up any aeronautical GPS to use true track is to pull the memory card 
I remember it from my IR training when the card suddenly gave up the ghost in a KLN94 installed in the school plane. Didn’t want to lose the booked flight, so I just entered the waypoint coordinates manually and off we went.
OK, that’s fine if your compass still works, because you just do the usual thing of flying a heading and you adjust the heading to line up the track ahead with the magenta line.
But if you have no meaningful heading (say, anywhere near the poles) then all you can do is to fly wings-level i.e.
Timothy flew to the N Pole a few years ago but unfortunately he has not posted any information here on how he did this stuff.
The G1000 has similar (or identical) limitations as shown with the G500. Actually, it is the the airplane’s limitation, placed accordingly in the limitation section of the AOM.
It is interesting that equipping an airplane with state-of-the-art does-everything-and-a-bit-more stuff squarely disqualified the aircraft from flying in large parts of the world.
I wonder how accurately you could find the magnetic poles with a magnetic inclinometer, looking for the points at which the magnetic fields are most vertical?
Yes, but the location would be inaccurate right after cos’ they move.
