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Page 2-8 G1000 / GFC 700 System Maintenance Manual - 300/B300 Series King Air
Revision 4 190-00716-01
2.1.11 Attitude & Heading Reference System (2)
The Garmin GRS 77 or GRS 7800 AHRS units provide attitude and heading information to the G1000
system. The units, mounted in the nose equipment bay, contain advanced tilt sensors, accelerometers,
and rate sensors. The unit interfaces with the Garmin Air Data Computers and GMU44 Magnetometer
and utilizes GPS signals from the GIA 63Ws. Actual attitude and heading information is sent using
ARINC 429 digital interface to both GDU 1040As and GIA 63Ws. The GRS interfaces with and
provides power to the GMU 44 Magnetometer. The GRS supplies attitude and heading information
directly to the PFDs, MFD, and GIAs. The #2 GRS AHRS units can provide heading data to an approved
third party TCAS II device through an ARINC 429 digital interface.
Additionally, the GRS 7800 AHRS provides heading with or without the aiding of the GMU 44
magnetometer. When operating without the aid of the magnetometer, the GRS 7800 is functionally
similar to that of a Directional Gyro.
GRS 1 receives primary electrical power from No. 1 Triple Fed Bus and a secondary power supply from
the Center Bus. GRS 2 receives electrical power from No. 3 Triple Fed Bus.
GRS 77 GRS 7800
Figure 2-10, AHRS
2.1.12 GMU 44 Magnetometer (2)
The GMU 44 provides horizontal and vertical magnetic field information to the GRS AHRS. This allows
heading to be calculated and provides assistance during AHRS alignment. The GMU 44 units are
mounted in the tailcone or in the horizontal stabilizer. The 011-00870-20 GMU 44 units may only be
installed in the horizontal stabilizer. The GMU 44 units were modified to account for low clearance
installations and have a 90-degree pig-tail harness versus the straight harness on the 011-08870-10 GMU
44 units. The units receive power directly from the GRS units and communicate with the GRS units via
RS-485 digital interface.
GMU 44 -00 & -10 Unit GMU 44 -20 Unit
Figure 2-11, Magnetometer