Navigation on Polar Routes

[tdracer]

This is just a curiosity question on my part.
Part of my job is that I sometimes review AFM revisions for accuracy in my area of expertise (engines). While it's not exactly applicable to me, I've often noticed notes on the Inertial Reference Systems that the IRS readings are 'valid' between 82 degrees north and south latitudes.
My question is,: what do you do if your flight path would take you higher than 82 degrees? Do you need to re-plan to a lower latitudes, or do you use other systems (e.g. GPS) when in the polar areas above 82 degrees? :confused:

Like I said, just curious :O

[MarkerInbound]

Guess it varies by type. On the 744 normally the three IRUs send their position to the FMC and it "triple mixes" the aircraft position. And the normally the left FMC is the master, feeding the right info. Above 84 degrees each FMC gets its it's own IRS and you lose the triple mix. So you could have a difference in the nav displays left and right. Above 88.5 degrees GPS is inhibited and you are unable RNP. The GPS will start updating again passing 88 degrees and below 83.5 degrees the IRUs triple mix again.

[underfire]

It does vary by type and the IRS. Some will go into ANP mode and RNP will be avail until ANP level reaches the associated RNP level.

Polar nav by aircraft type (Boeing) (http://www.boeing.com/commercial/aeromagazine/aero_16/polar_nav_by_model.html)

EDIT: Curiosity....NPOLE 90° 0' 0N 0° 0' 0W Mag Var: 18.401W

[Ozlander1]

The old Delco INS could navigate over the poles, the big question for it was, which heading to take since they were all 180*.

[Desert185]

Flying Antarctica, we go to true around 60 South. If at the pole, going north in the correct direction is not really confusing because of the longitude of the next fix.