Garmin G5 Pilot's Manual page 19

1.4.1.2 G5 HEADING
The G5 can display magnetic heading information received from the GMU 11
magnetometer. If magnetic heading input data is not available, the G5 will display
GPS-derived ground track and the heading field will have a red 'X' displayed.
Figure 1-7 Heading Fail (PFD Page)
If both magnetic heading and GPS are unavailable, the heading field will have a red
'X' displayed and the compass card will be removed from the HSI.
Figure 1-9 Heading/Track Fail (PFD Page)
The G5 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 5 years via a software
update. Failure to update this database could lead to erroneous heading information
being displayed to the pilot.
If the G5 senses the magnetic heading measurement is valid but possibly outside of
the internal accuracy limits, the numeric heading is displayed in yellow.
If the GAD 29B fails, VFR will be displayed in amber text and GPSS will be displayed
in amber text, if GPSS mode is selected.
Figure 1-11 GAD 29B Fail (Amber VFR)
190-01112-12 Rev. F G5 Electronic Flight Instrument Pilot's Guide for Certified Aircraft
System Overview
Figure 1-8 Heading Fail (HSI Page)
Figure 1-10 Heading/Track Fail (HSI Page)
Figure 1-12 GAD 29B Fail (Amber GPSS)
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