FCOM.1
High Latitude Operations
The heading reference for PFDs, NDs, and RMI changes to true north at 82N (or north of 70N between 80W and 130W) or at 82S (or south of 60S between 120E and 160E).
At latitudes between 82N (or south of 70N between 80W and 130W) and 82S (or north of 60S between 120E and 160E), the FMC and IRU reference is determined by Heading Reference switch position. Outside this region, the FMC and IRUs reference true north regardless of Heading Reference switch position.
Automatic switching to a true north reference annunciates by a flashing white box around the word TRU on the ND. A TRUE heading reference can be selected with the Heading Reference switch inside or outside high latitudes.
The ND displays a green box around the word MAG to annunciate the change back to magnetic reference. If the heading reference is TRU in the descent phase, the ND displays an amber box around the word TRU.
Note: For autopilot operation in high latitudes using a roll mode other than
LNAV, the TRUE position on the Heading Reference switch should be
selected.