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190-00728-04 Rev. A
Embraer Prodigy
®
Flight Deck 100 Pilot’s Guide
29
SYSTEM OVERVIEW
AHRS OPERATION
NOTE: Refer to the Appendices for specific AHRS alert information.
NOTE: Aggressive maneuvering while the AHRS is not operating normally can degrade AHRS accuracy.
In addition to using internal sensors, the GRS 77 AHRS uses GPS information, magnetic field data and air
data to assist in attitude/heading calculations. In normal mode, the AHRS relies upon GPS and magnetic field
measurements. If either of these external measurements is unavailable or invalid, the AHRS uses air data
information for attitude determination. Four AHRS modes of operation are available (see Figure 1-23) and
depend upon the combination of available sensor inputs. Loss of air data, GPS, or magnetometer sensor inputs
is communicated to the pilot by message advisory alerts.
Attitude/Heading Invalid
AHRS
no-GPS
Mode
AHRS Normal
Operation
AHRS no-
Mag Mode
AHRS no-Mag/
no-Air Mode
Heading Invalid
available
available
unavailable
unavailable
available
unavailable
unavailable
available
Air Data
Magnetometer Data
unavailable
available
GPS Data
Magnetometer Data
Air Data
Figure 1-23 AHRS Operation
The AHRS (GRS 77) corrects for shifts and variations in the Earth’s magnetic field by applying the Magnetic
Field Variation Database. The Magnetic Field Variation Database is derived from the International Geomagnetic
Reference Field (IGRF). The IGRF is a mathematical model that describes the Earth’s main magnetic field and
its annual rate of change. The database is updated approximately every five years. See the Appendices for
information on updating the Magnetic Field Variation Database. The system will prompt the pilot on startup
when an update is available. Failure to update this database could lead to erroneous heading information being
displayed to the pilot.