NAVIGATION AND
COMMUNICATION
AIRPLANE
OPERATIONS
MANUAL
2-18-30
Page
6
Code
02
MARCH 30, 2001
NOTE: To complete the alignment, the IRU requires a valid input of
the airplane’s present position (latitude and longitude) from the
FMS.
If the present position is not entered during the normal alignment time,
the MSU ALIGN annunciator flashes and the IRS 1 (2) ALN FAIL
caution message (only for airplanes equipped with EICAS 17 onwards)
will be presented on the EICAS. The IRU will not complete the
alignment phase and/or will not enter the NAV mode until it receives a
valid position input from the FMS.
The IRU accepts multiple entries of latitude and longitude. More than
one entry may be necessary to confirm, update or correct the position.
However, the IRU does not accept new position inputs until 2 seconds
after the previous input. A new position entry overwrites the previous
entry, and the IRU uses only the latest entry for its calculations. The
IRU conducts a position comparison test on latitude and longitude
immediately after each data has been entered. To pass the test, the
entered data must compare within 1 degree of the stored
latitude/longitude from the last power down from the NAV mode. If the
test fails, the MSU ALIGN annunciator flashes and an IRS 1 (2) ALN
FAIL caution message (only for airplanes equipped with EICAS 17
onwards) will be presented on the EICAS.
No attitude and heading is displayed during align mode.
MSU SET FROM NAV TO ALIGN OR NAV TO ALIGN AND BACK TO
NAV (TO BE USED ON THROUGH FLIGHTS):
This command will revert the IRU to the align down-mode, which
zeroes residual velocity errors accumulated during the previous
navigation mode operation. The fine leveling process of the align mode
is reactivated, and heading accuracy is updated. When the IRU enters
the align down-mode, the ALIGN annunciator illuminates and an IRS 1
(2) ALN advisory message is presented on the EICAS (only for
airplanes equipped with EICAS 17 onwards).
The airplane must be stationary (ground speed less than 20 knots)
during the align down-mode otherwise an automatic full realignment
will begin in 30 seconds after an excessive aircraft motion stops.
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