AIRPLANE
OPERATIONS
MANUAL
NAVIGATION AND
COMMUNICATION
JUNE 28, 2002
2-18-30
Page
1
Code
02
INERTIAL REFERENCE SYSTEM (IRS)
As a replacement for the Attitude and Heading Reference System
(AHRS), the EMB-145/135 airplane family may be equipped with two
identical and independent Inertial Reference Systems (IRS). Aside
replacing AHRS functions, the dual IRS installation is used as an
additional navigation sensor for the FMS, and it may also provide
accurate attitude and heading data to the Head-Up Guidance System
(HGS), when this equipment is installed.
Another possibility for HGS-equipped airplanes is the installation of a
single IRS tailored for that equipment, while PFDs, MFDs and RMUs
receive information from two AHRS.
Basically, the IRS provides attitude and heading reference data for the
airplane displays and navigation data for the FMS by sensing linear
motion and angular rates through inertial sensors.
The IRS interface with the airplane’s systems and equipment is as
follows:
− Air Data Computers (ADC 1 and ADC 2): The IRS 1 and IRS 2
receive altitude, altitude rate and true airspeed information from the
ADC 1 and ADC 2 respectively, to improve the precision of computed
navigation data.
− Integrated Computers (IC1 and IC2): The IRS 1 and IRS 2 provide
pitch, roll and heading information to the respective PFD, and
heading information to the respective MFD, through the IC-600s.
Data is transmitted separately to both sides, to ensure that a single
IC failure does not compromise the data path.
− Radio Management units (RMU 1 and RMU 2): the IRS 1 provides
heading information to both RMUs via DAU 2.
− Autopilot System: The IRS 1 provides pitch, roll and acceleration
information to the Autopilot System via IC-600-1.
− Weather Radar: The IRS 2 provides attitude information to the
Weather Radar for antenna stabilization.
− Flight Management System (FMS): The IRS provides attitude,
heading and navigation information to the FMS. The IRS receives
position, magnetic heading, UTC time and date from the FMS.
− EGPWS/GPWS: The IRS 1 provides attitude and heading
information to the EGPWS/GPWS.
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