Grs 77; Gmu 44 - Garmin G500 Pilot's Manual

1.1.4

GRS 77

The GRS 77 is an Attitude and Heading Reference System (AHRS) unit that
provides aircraft attitude information to the G500 display. The unit contains
advanced tilt sensors, accelerometers, and rate sensors. In addition, the GRS 77
interfaces with both the GDC 74A Air Data Computer and the GMU 44
magnetometer. The GRS 77 also utilizes GPS data forwarded from the GDU
620. Actual attitude and heading information is sent to the GDU 620 using an
ARINC 429 digital interface.
The IGRF (International Geomagnetic Reference Field) model is contained in
the GRS 77 and is only updated once every five years. The IGRF model is part
of the Navigation Database. At system power-up, the IGRF models in the GRS
77 and in the Navigation Database are compared, and if the IGRF model in the
GRS 77 is out of date, the user is prompted to update the IGRF model in the
GRS 77. The prompt will appear after the G500 splash screen is acknowledged
on the MFD.
1.1.5

GMU 44

The GMU 44 magnetometer senses the earth' s magnetic field. Data is sent to
the GRS 77 AHRS for processing to determine aircraft magnetic heading. This
unit receives power directly from the GRS 77 and communicates with the GRS
77 using a RS-485 digital interface.
1-4
Figure 1-4 GRS 77 AHRS
Figure 1-5 GMU 44 Magnetometer
Garmin G500 Pilot's Guide 190-01102-02 Rev. B