9.5 FMC/Autopilot Performance Near The Pole
Changes in FMC updating approaching the pole are described in the Navigation chapter (FMC Polar Operations) of the Flight Manual. Review these pages before conducting polar operations. The North Pole is in the FMS database and coded NPOLE. Do not fly directly over the pole due to the possibility of the autopilot reacting aggressively when passing over the pole due to the abrupt 180 change in the orientation of the compass. This may occur in any autopilot roll mode : LNAV, HDG SEL, or HDG HOLD.
Note : As of the date of this document, there is a software fault in the FMC which is created by even moderate winds over the polar region. Failure of the FMC to accurately account for the significant direction changes of the enroute winds, can result in the FMC providing down track waypoint time and fuel estimates that are grossly inaccurate. This often results in an INSUFFICIENT FUEL message due to the predictions of time and fuel to the destination. The current active waypoint ETA reflected on the ND should still be accurate however, since this ETA is derived from dynamic data and is not affected by this anomaly. Normally the FMC corrects this time and regains normal functionality within 1 to 2 hours. Use the flight plan estimates for making position reports.
The FMC starts polar operations when the calculated airplane position enters a Polar Region. The FMC switches all flight display inputs to reference true north while in these regions. GPS provides navigation data to the FMC throughout the Polar Regions. If GPS information is lost, the ADIRU provides a single inertial navigation position to the FMC to ensure continuous navigation throughout the Polar Regions. A flashing white box around the word TRU on the ND annunciates automatic switching to a true north reference. A TRUE heading reference can be selected with the HEADING REFERENCE switch inside or outside the Polar Region. The ND displays a green box around the word MAG to