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Attitude alignment takes 1 minute from power OFF to ATT mode or 34 seconds from
NAV to ATT mode, provided the airplane is stationary on the ground or in straightand-
level flight. The IRS ALIGNING DO NOT TAXI message appears on the PFD on
ground or IRS ALIGNING message appears in flight.
If excessive motion is detected, the attitude alignment is run for an additional 20
seconds. Once attitude alignment is complete, a free DG heading operation is
available. Heading is entered from the FMS CDU IRS CONTROL page via the SET
IRS HDG prompt. Heading entries are periodically required while the IRS is in
attitude mode to correct for heading drift.
Attitude Mode
Figure 17-5
NOTE
P604_17_068
N
33
30
W
3
10
20
DG 340
DG
FMS1 IRS CONTROL
IRS2 <ENABLED>
IRS3 <ENABLED>
<INDEX
- - - °/ - . -
265 °/ 0.0
- - - >
265 °/ 0.0
DRIFT
DRIFT
DRIFT
POS DIFF
- . - NM/HR
- . - NM/HR
- . - NM/HR
- - - - - - - - - - - - SET IRS HDG
[ ]
SET IRS HDG
IRS1 <ENABLED>
NAVIGATION SYSTEMS
For Training Purposes Only
May 03
17-11
P I LOT T R A I N I N G GU I D E
IRS Shutdown
The recommended method of shutting down the IRS is by setting the MSU selector
switch to OFF. During this shutdown process, the IRU will remain powered for an
additional 10 seconds to allow system record storage (aircraft power should not be
removed until 15 seconds after the MSU is selected OFF).
To ensure proper system record storage, it is also recommended to keep the IRS in
NAV mode for a minimum of three minutes after the aircraft is parked.
Record storage at shutdown consists of the Elapsed Time Indicator (ETI) record
update and NAV updates which are required to ensure the best possible alignments and
NAV performance. If power is removed from the IRU during the 10-second shutdown,
then NAV updates and ETI may not be stored.
Operating Tips
The IRS manufacturer recommends the following operating tips:
PHASE OF FLIGHT RECOMMENDATIONS
Alignment For best performance the IRS should be aligned at random headings. Continuous
alignments at or near one cardinal heading may degrade performance.
Initial position entry
Initial latitude and longitude should be entered within two minutes of start-up.
The initial latitude and longitude position should be within 1 nautical mile of actual
aircraft position to ensure the most accurate IRS alignment.
Prior to taxi
It is recommended to remain in NAV mode prior to taxi for at least five minutes. The
IRS continues to adjust for bias errors and temperature changes as long as the aircraft
is stationary.
Taxi
If practical, it is recommended that the aircraft stops during taxi for a period of one to
three minutes with a heading 90 to 180 degrees different than the alignment heading.
NAV updates are performed during taxi but will not be used unless the aircraft has
stopped for a minimum of one minute.
Intermediate stops
During intermediate stops, it is recommended to use the Rapid Realign feature when
the IRS remains on during the stop. This will minimize drift errors during subsequent
flights as drift error is zeroed.
Post-flight
Keep the IRS on for a minimum of three minutes after the aircraft is parked. After the
IRS is turned off with the mode select switch, keep the power applied for a minimum of
15 seconds to allow storing of the Nav Update records in the IRS memory.
IRS Operating Tips
Table 17-3
NAVIGATION SYSTEMS
17-12 For Training Purposes Only
May 03
P I LOT T R A I N I N G GU I D E
Controls and Indicators
IRS Mode Select Unit (MSU)
Figure 17-6
IRS Reversionary Mode Selectors (Dual IRS Configuration)
Figure 17-7
P604_17_069
OFF
NAV
ATT OFF
NAV
ATT
1 IRS 2
OFF
NAV
ATT
3 IRS
IRS 1/2 Mode Selector Switches
OFF
NAV
ATT
- Removes power from IRS
-Selected for normal operation
- Selected for reversionary
P604_17_070
IRS Reversionary Mode Selector Switch
1 - Pilot’s and copilot’s systems receive IRS
data from IRS 1
NORM - Pilot’s and copilot’s systems receive
data from their on-side system
2 - Pilot’s and copilot’s systems receive IRS
data from IRS 2
PFD EICAS
NORM
L MFD
1 2
NORM
ADC
1 2
NORM
DCP
EICAS PFD
NORM
R MFD
ED
1
ED
NORM
EICAS
D EIC
2
　
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