Originally Posted by
PerfInit
Gotta run them IRU's in "TRUE" versus Mag and don't forget to monitor your fuel temps. "Fuel Freeze" is an issue for long flights over the poles.
Actually, all IRS and GPS units only think in True. They can display Magnetic if the pilot chooses by consulting an internal database of Lat Long magnetic variation.
On the 747-400, if you left the Mag/True switch in Mag, the display switched over to true automatically at around 80 North while heading north, and then switched back to Mag when you got back down to around 80 North on the southbound leg.
Joe