NAVIGATION AND
COMMUNICATION
AIRPLANE
OPERATIONS
MANUAL
2-18-30
Page
14
Code
02
MARCH 30, 2001
IRS CONTROLS AND INDICATORS
MSU CONTROL PANEL
1 - TEST SWITCH
TEST
− − When the TEST switch is pressed the IRU enters
the self-test sub-mode.
2 - ANNUNCIATORS
ALIGN
− − Indicates that the IRU is in the align mode. A
flashing ALIGN annunciator indicates that
latitude/longitude was not accepted by the IRU.
FAULT
− − Indicates an IRU fault.
ON BATT
− − Indicates that the IRU is being powered by the
airplane batteries.
BATT FAIL
− − Indicates that the airplane batteries are incapable
of sustaining IRS operation on backup power
operation.
NAV RDY
− − Indicates that alignment is complete, if the MSU
switch is set to ALIGN.
NO AIR
− − Indicates that cooling air is inadequate to cool the
IRU.
3 - MODE SELECTOR SWITCH
− OFF: the IRU circuitry is OFF. However, when the IRU is
operating and the MSU switch is moved from another position to
OFF, there will be a delay of 3 seconds before the IRU starts the
power-down routine, in order to prevent its inadvertent selection.
− ALIGN: once this mode is selected the IRU starts the full
alignment or alignment down-mode. ALIGN annunciator is ON
and an IRS 1 (2) ALN advisory message is presented on the
EICAS (only for airplanes equipped with EICAS 17 onwards).
− NAV: there is a detent in the NAV position. The switch must be
pulled out of the detent to be moved to another position.
− ATT: if the MSU switch is placed at this position, after 2 seconds
(time delay incorporated to prevent inadvertent selection of the
ATT mode) the IRU enters the erect attitude sub-mode for 20
seconds, during which the ALIGN annunciator illuminates. Then
the IRU enters the attitude mode. On airplanes equipped with
EICAS 17 onwards, the IRS 1 (2) ATT MODE caution message
will be presented on the EICAS. On the ground, the MSU switch
must be set to OFF for at least 3 seconds before the ALIGN or
NAV mode can be re-established.
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