Garmin G3X Pilot's Manual page 48

System Overview
If GPS input fails, 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 Page 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. Likewise, loss of magnetometer
(heading) data, in combination with loss of GPS data results in a loss of all attitude
and heading information.
In installations that include multiple AHRS units (G3X supports up to three AHRS
sources) if data from an AHRS source is lost the G3X will automatically switch sources,
when a failure is detected. Reversionary sensor selection is annunciated in a window
on the right side of the PFD. These annunciations reflect reversionary sensors selected
on the PFD. Pressing the Menu Key while on the PFD page accesses the PFD Setup
page, select the Sensors Softkey, turn the FMS Joystick to select the desired ADAHRS
source (AUTO, ADAHRS1, ADAHRS2, or ADAHRS3) softkeys. This allows for
manual switching of the ADAHRS sensors being viewed on the PFD. The GPS sensor
cannot be switched manually.
In the example below a GSU 73 is configured as ADAHRS1 and a GSU 25 is
configured as ADAHRS2. ADAHRS1 has failed, the system has auto filled the AHRS
information from AHRS2 as annunciated in the Reversionary Sensor Window to the
right of the HSI. Since the GSU 73 also processes the engine and airframe data, engine
and airframe data is lost as indicated by the red 'Xs'.
26
Garmin G3X Pilot's Guide 190-01115-00 Rev. K