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747 Operations Manual
Copyright © The Boeing Company. See title page for details.
11.20.2 D6-30151-425
Flight Management, Navigation -
Navigation Systems Description
GPS System Schematic
GPS
TRANSMITTER
TRANSMITTER
GPS
GPS RECEIVER
- LEFT - RIGHT
GPS RECEIVER
ANTENNA ANTENNA
430 MLS
300 /35 1400.0
221.3
GPS
320 DPR
FSD
MLS
GS
NM
Z
GPS
TRANSMITTER
TRANSMITTER
GPS
GPS
RECEIVERS
Map Display
Nav Mode
GPS Position Symbol
FMS Position
FLIGHT MANAGEMENT COMPUTER DISPLAYS FUNCTION
TAS 465
Update Status
POS REF 2 /
F M C G S
N4 K T
I R
N K T
<INDEX >
0
4
<PURGE
3
P O S ( G P S L )
S ( 3 )
4
4 3
26
R N P / A C T U A L N A V S T A
1 . 0 / N M
---------------- G P S N A V
B R G / D I S T
I N H I B I T >
0
7`32. W122`18.7
7`32.4 W122`18.6
4
FMC
Position
0 30
.
.
October 1, 2000
747 Operations Manual
Flight Management, Navigation -
Navigation Systems Description
Copyright © The Boeing Company. See title page for details.
D6-30151-425 11.20.3
Inertial Reference System
The inertial reference system (IRS) calculates airplane position, acceleration,
track, vertical speed, ground speed, true and magnetic heading, wind speed and
direction, and attitude data for the displays, flight management system, flight
controls, engine controls, and other systems. The IRS consists of three inertial
reference units (IRUs) and the IRS mode selector panel.
IRS Alignment
Full Alignment
Rotating the IRS mode selector from OFF to NAV begins IRS alignment.
Alignment requires approximately ten minutes. Present position (latitude and
longitude) must be entered on the CDU position initialization page to complete
alignment. Alignment can be accomplished only when the airplane is parked.
Alignment stops if an IRU detects motion during alignment. Alignment continues
and completes in approximately ten minutes after motion stops. The IRS is aligned
when all IRUs enter the navigation mode. Latitude and longitude entries then
blank on the SET IRS POS line on the CDU position initialization page.
Alignment is lost if the selector is moved out of theNAV position.
A full alignment, accomplished by rotating the IRS mode selector to OFF and
back to NAV, must be accomplished when the time from the last full alignment to
the next expected arrival time exceeds 18 hours.
Fast Alignment
Following operation in the navigation mode and with the airplane parked,
performing a fast alignment removes accumulated track, ground speed, and
attitude errors, relevels the system, and updates present position. This is
accomplished by positioning selectors to ALIGN, entering present position, and
repositioning selectors to NAV. Fast alignment completes in approximately 30
seconds.
Fast alignment can be accomplished without entering present position. However,
greater navigational accuracy is attained by entering present position.
IRS Attitude
If alignment is lost in flight, the navigation mode is inoperative for the remainder
of the flight. Attitude information can be obtained by moving the selector to ATT.
The IRU enters align mode for 30 seconds. This relevels the system and provides
attitude displays on the PFD. For best accuracy, the airplane must be in straight
and level flight. Some attitude errors may occur during acceleration. After
acceleration, errors are slowly removed.
December 01, 1999
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
11.20.4 D6-30151-425
Flight Management, Navigation -
Navigation Systems Description
The attitude mode can also provide heading information. A magnetic heading
input is required to initialize the IRU while in attitude mode. This heading is
available for backup if all three IRUs fail. Heading information displayed on the
PFD and ND is from an IRU operating in the navigation mode. This information
is independent of the IRS source selector position if an operating FMC is selected
by the navigation source selector.
IRS Power
The IRS can operate onAC or DC power. The center IRU operates on DC power
for five minutes, then shuts down. If an IRU loses both AC and DC power,
alignment is lost.
Radio Navigation Systems
Automatic Direction Finding (ADF)
ADF Tuning
Two ADF receivers can be manually tuned from the left or right CDU on the NAV
　
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