190-00820-08 Rev. A
Cirrus Perspective
™
by Garmin – Pilot’s Guide for the SR20/SR22/SR22T
32
SYSTEM OVERVIEW
SY
STEM
O
VER
VIEW
FLIGHT
INSTRUMENTS
EIS
AUDIO P
ANEL
& CNS
FLIGHT
MANA
GEMENT
HAZARD
AV
OID
ANCE
AFCS
ADDITIONAL FEA
TURES
APPENDICES
INDEX
AHRS OPERATION
NOTE:
Aggressive maneuvering in reversionary mode can degrade AHRS accuracy.
The Attitude and Heading Reference System (AHRS) performs attitude, heading, and vertical acceleration
calculations for the system, using GPS, magnetometer, and air data in addition to information from its internal
sensors. Attitude and heading information are updated on the PFD while the AHRS receives appropriate
combinations of information from the external sensor inputs.
Attitude/Heading Invalid
AHRS
no-GPS
Mode
AHRS Normal
Operation
AHRS no-
Mag Mode
AHRS no-Mag/
no-Air Mode
Heading Invalid
av
ailab
le
av
ailab
le
una
va
ilab
le
una
vailab
le
av
ailab
le
una
va
ilab
le
una
va
ilab
le
av
ailab
le
Air Data
Magnetometer Data
una
va
ilab
le
av
ailab
le
GPS Data
Magnetometer Data
Air Data
Figure 1-23 AHRS Operation
Loss of GPS, magnetometer, or air data inputs is communicated to the pilot by message advisory alerts (refer
to Appendix A for specific AHRS alert information). Any failure of the internal AHRS inertial sensors results in
loss of attitude and heading information (indicated by red ‘X’ flags over the corresponding flight instruments).
Two GPS inputs are provided to the AHRS. If GPS information from one of the inputs fails, the AHRS uses
the remaining GPS input and an alert message is issued to inform the pilot. If both GPS inputs fail, the AHRS
can continue to provide attitude and heading information to the PFD as long as magnetometer and airspeed
data are available and valid.
If the magnetometer input fails, the AHRS continues to output valid attitude information; however, the
heading output on the PFD is flagged as invalid with a red ‘X’.
Failure of the air data input has no effect on the AHRS output while AHRS is receiving valid GPS information.
Invalid/unavailable airspeed data in addition to GPS failure results in loss of all attitude and heading information.
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
Summary of Contents for Cirrus Perspective SR20
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