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)
EDIT: Curiosity....NPOLE 90° 0' 0N 0° 0' 0W Mag Var: 18.401W
Last edited by underfire; 10th Dec 2013 at 22:09.