AIRPLANE
OPERATIONS
MANUAL
NAVIGATION AND
COMMUNICATION
MARCH 30, 2001
2-18-30
Page
1
Code
01
ATTITUDE AND HEADING REFERENCE SYSTEM
(AHRS)
On EMB-145/135 airplanes, the equipment responsible for generating
attitude and heading data is the Attitude and Heading Reference
System (AHRS). Optionally the AHRS may be replaced by the Inertial
Reference System (IRS) that, aside generating attitude and heading
data, may still provide position information to the Flight Management
System (FMS).
There are two types of AHRS installed on EMB-145/135 airplanes: the
AH-800 and the AH-900.
Regardless of version, the airplane is equipped with two identical and
independent units, identified as AHRS 1 and AHRS 2.
The interface of the AHRS with other systems and equipment of the
airplane is the following:
− Air Data Computers (ADC 1 and ADC 2): The AHRS 1 and AHRS 2
receive true airspeed information from the ADC 1 and ADC 2
respectively, to improve the precision of the computed navigation
data.
− Integrated Computers (IC1 and IC2): The AHRS 1 and AHRS 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 single IC
failure does not compromise the data path.
− Radio Management Units (RMU 1 and RMU 2): The AHRS 1
provides heading information to both RMUs via DAU 2.
− Autopilot System: The AHRS 1 provides pitch, roll and acceleration
information to the Autopilot System via IC-600-1.
− Weather Radar: The AHRS 2 provides attitude information to the
Weather Radar for antenna stabilization.
− Flight Management System (FMS): The AHRS provides attitude and
heading information to the FMS.
− EGPWS/GPWS: The AHRS 1 provides attitude and heading
information to the EGPWS/GPWS.
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