Embraer EMB145 Operation Manual page 2470

NAVIGATION AND
AIRPLANE
COMMUNICATION
OPERATIONS
MANUAL
This mode provides a quick attitude restart: during the first 20 seconds
the IRU enters the erect attitude transitional mode. In this transitional
mode the IRU computes a new level axis set. The airplane must be
held steady, straight and level until the MSU ALIGN annunciator
extinguishes itself and an IRS 1 (2) ALN advisory message (only for
EICAS 17 onwards) disappears from the EICAS.
When operating in the attitude mode the IRS 1 (2) ATT MODE caution
message (only for airplanes equipped with EICAS 17 onwards) is
presented on the EICAS. In this mode, attitude outputs are not as
accurate as when operating in the NAV mode, and magnetic heading
must be entered periodically through the FMS Control Display Unit.
POWER-OFF MODE
The IRU enters the power-down mode when the MSU switch is set to
OFF and remains in that position for 3 seconds (to prevent inadvertent
selection). After that, power continues for 10 to 15 seconds to transfer
the last calculated latitude and longitude and other IRS parameters to
its non-volatile memory. The ALIGN annunciator illuminates when the
IRU is in the power-down mode (and an IRS 1 (2) ALN advisory
message is presented on the EICAS, for airplanes equipped with
EICAS 17 onwards).
NOTE: The airplane must not be de-energized before the ALIGN
annunciator light extinguishes.
De-energizing the airplane before the ALIGN annunciator extinguishes
itself (and an IRS 1 (2) ALN advisory message is removed from the
EICAS, on airplanes equipped with EICAS 17 onwards) may interrupt
the transferring process of the IRU's last calculated position and other
IRS parameters to its non-volatile memory, which will affect the next
alignment.
TEST MODE
The test mode is selected by pressing the MSU test switch. The test
mode can be selected in either the align mode or the NAV mode
without affecting basic IRS function. The test mode is inhibited in the
attitude mode and in the NAV mode when aircraft ground speed
exceeds 20 knots.
Page Code
8 02
2-18-30 MARCH 30, 2001