SUPPLEMENT SG-3
CHAPTER 31 - INDICATIONG SYSTEM
GRS 77 (AHRS)
The GRS 77 is an attitude and heading reference unit, or AHRS, that provides aircraft
attitude and flight characteristics information to the GDU 620. The unit contains ad-
vanced tilt sensors, accelerometers, and rate sensors. In addition, the GRS 77 interfaces
with both the GDC 74( ) air data computer and the GMU 44 magnetometer. The GRS
77 also utilizes GPS signals sent from the GPS/SBAS navigator. Actual attitude and
heading information is sent using ARINC 429 digital interface to the GDU 620 and op-
tional GAD 43 adapter.
GMU 44
The GMU 44 magnetometer senses magnetic field information. 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 an RS-485
digital interface.
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