Embraer EMB145 - Page 2469

AIRPLANE
OPERATIONS
MANUAL
NAVIGATION AND
COMMUNICATION
MARCH 30, 2001
2-18-30
Page
7
Code
02
AUTOMATIC NAVIGATION REALIGNMENT (ANR):
The ANR is entered automatically and concurrently with normal mode
operations, when the IRU senses that the airplane has completed a
“no motion period” (between 7.5 and 15 minutes, as a function of
latitude). In the ANR sub-mode, the IRU applies corrections by zeroing
velocities, resetting the attitude platform, and correcting heading errors
accumulated during the previous navigation mode operation. When the
IRU enters the ANR sub-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).
NAVIGATION MODE
The IRU enters the NAV mode after completing its alignment when the
IRU MSU switch is set to NAV. In the NAV mode, the IRU uses the last
valid position data entered during the align mode or align down-mode
as its initial present position and updates the present position based
only on inertial data while it remains in the NAV mode. The IRU
algebraically adds computed magnetic variations from a magnetic
variation topographical map (MAGVAR) to true heading and true track
to produce magnetic heading and track magnetic angle. The magnetic
heading and magnetic tracking angle outputs are set to no computed
data (NCD) inside a northern and southern latitude cutout area.
ATTITUDE MODE
The attitude mode is the IRU’s reversionary mode. It is automatically
entered by the IRU if it experiences in-flight loss of power, or it may be
selected by the crew if the FAULT annunciator lights and an IRS 1 (2)
FAIL caution message is presented on the EICAS (only on airplanes
equipped with EICAS 17 onwards), indicating a critical fault, that
invalidates all outputs.
CAUTION: THE MSU SWITCH MUST NOT BE SET TO ATTITUDE
MODE INADVERTENTLY. IF THIS OCCURS ON THE
GROUND, IT IS NECESSARY TO SET THE MSU
SWITCH TO OFF FOR AT LEAST 3 SECONDS, THEN
BACK TO ALIGN OR NAV. IF ATTITUDE MODE IS SET
IN-FLIGHT, IT IS NOT POSSIBLE TO RECOVER THE
NAV MODE.