Here:
737-600/-700/-800/-900.
The primary roll mode for polar operations should be LNAV. The heading reference switch must be in the TRUE position to enable flight control computer engagement, HDG SEL mode, ROLL CWS mode, and heading display on the RMI. Deviations from the planned route may be accomplished in HDG SEL mode.
Differences between the heading display on the PFD/ND and the RMI may exist within approximately 30 nmi of a pole because of differences between the FMC position and IRS position. For GPS-equipped airplanes, loss of both GPS units results in an increased ANP and possible display of the UNABLE REQD NAV PERF-RNP annunciation, but this normally would not prevent polar operation.
Loss of one IRU does not significantly affect navigation accuracy. Operation on the remaining IRU should be limited to diversion to the nearest suitable airport.
In the event of dual IRU failure, the left GPS true track is displayed on page 3 of the PROGRESS pages on the CDU. This serves as a tertiary backup for the airplane heading or track and an update to IRS ATT mode.
Polar navigation option.
These latitude limitations on flight operation do not apply to 747-400, 777, and 737-600/-700/-800/-900 airplanes equipped with the polar navigation option (heading reference switch and FMC Update U10.3 or later) and dispatched with the following equipment operational: CDU, left GPS, both IRUs in navigation (NAV) mode, and both display electronic units.
Flight crews of such equipped airplanes should not use HDG SEL or ROLL CWS north of 89 deg 30 min north latitude or south of 89 deg 30 min south latitude. They also should not use the heads-up display system, if installed, when the heading reference switch is in TRUE.
Aero 16 - Polar Route Navigation By Model
The flight/nav specifications vary by model and year. As 737's and navigation techniques in general, improve, more can be done by way of polar flight.
