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84°N or south of 84°S. FMCs revert to split IRS operation, the CDU message
SPLIT IRS OPERATION displays, and each FMC connects to a different IRU.
Radio update corrections are lost and FMCs incrementally remove the difference
between FMC and IRU positions.
Split IRS operation may result in differences between Captain’s and F/O’s NDs if
GPS updating is not available.
When GPS is available, GPS updating continues until the FMC position passes
north of 88.5°N or south of 88.5°S. At this point, GPS update corrections are lost
and the FMC position becomes a single IRU position. When the FMC position
passes south of 88.5°N or north of 88.5°S, GPS updating resumes.
When both FMC positions pass south of 83.5°N or north of 83.5°S latitude, FMCs
return to normal operation using the triple mixed IRU position.
Primary FMC Position Update Source POS REF page
2/3
ND Annunciation
GPS valid, LOC invalid GPS L, GPS R GPS
LOC, GPS valid* LOC–GPS LOC GPS
LOC, DME DME valid; GPS invalid* LOC–RADIO LOC DD
LOC, VOR DME valid; GPS invalid* LOC–RADIO LOC VD
LOC valid; GPS, DME, VOR invalid* LOC LOC
DME valid; GPS invalid RADIO DD
VOR DME valid; GPS invalid RADIO VD
GPS, VOR, DME invalid INERTIAL IRS(X)
* The FMC changes to LOC updating when:
• the tuned localizer is associated with the destination runway
• the airplane is less than 6,000 feet above the navaid elevation
• the airplane track is within 45° of the localizer course for a frontcourse
approach or 135° for a backcourse approach
• the airplane is less than 20 nm from the localizer navaid for a
frontcourse approach or less than 12 nm for a backcourse approach
• the airplane is within 25° of the localizer center for a frontcourse
approach or 155° for a backcourse approach
April 01, 2001
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
11.31.8 D6-30151-425
Flight Management, Navigation -
Flight Management System
Operation
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.
Areas of High Latitude Operations (with expanded MAGVAR)
80°W
160° E
82° N
120° E
70° N
True North Pole
130°W
True South Pole
82° S
60° S
October 1, 2000
747 Operations Manual
Flight Management, Navigation -
Flight Management System
Operation
Copyright © The Boeing Company. See title page for details.
D6-30151-425 11.31.9
Navigation Performance
The FMC uses data from navigation systems to accurately calculate the position
of the airplane. The current FMC position is on line 1 of the POS REF page 2. The
primary source of update is in parentheses above the FMC position. The inertial
reference system position is on line 2. The FMC position displays on the ND at
the tip of the triangle. The IRS position displays relative to the FMC position. The
ACTUAL navigation performance circles shown below do not display on the ND.
October 1, 2000
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
11.31.10 D6-30151-425
Flight Management, Navigation -
Flight Management System
Operation
POS R EF 2 /
F M C G S
N 4 K T
I R
N K T
< IND EX >
0
4
< PUR GE
3
P O S ( G P S L )
S ( 3 )
4
4 3
2 6
R N P / A C T U A L D M E - D M E
2 . 0 / N M
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