When does HDG go to TRUE? 744
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When does HDG go to TRUE? 744
Got a question regarding the 744.
At what laititude N and what lat. S does the switch go to TRUE? Does this depend from the different SOP? Does the IRS do this automatically?
Some insight would be great!
Leo
At what laititude N and what lat. S does the switch go to TRUE? Does this depend from the different SOP? Does the IRS do this automatically?
Some insight would be great!
Leo
Join Date: Jun 2005
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FCOM.1
High Latitude Operations
The heading reference for PFDs, NDs, and RMI changes to true north at 82��N (or north of 70��N between 80��W and 130��W) or at 82��S (or south of 60��S between 120��E and 160��E).
At latitudes between 82��N (or south of 70��N between 80��W and 130��W) and 82��S (or north of 60��S between 120��E and 160��E), 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.
High Latitude Operations
The heading reference for PFDs, NDs, and RMI changes to true north at 82��N (or north of 70��N between 80��W and 130��W) or at 82��S (or south of 60��S between 120��E and 160��E).
At latitudes between 82��N (or south of 70��N between 80��W and 130��W) and 82��S (or north of 60��S between 120��E and 160��E), 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.
