Grs 77/Gmu 44; Equipment Description - Garmin G900X Installation And Maintenance Manual

7. GRS 77 and GMU 44

7.1 Equipment Description

The Garmin GRS 77 AHRS (Attitude and Heading Reference System) and GMU 44 Magnetometer are
remote mounted devices that provide flight attitude and heading data for flight instrumentation. With
information available and valid from all sensors, or without the GPS, the GRS 77 AHRS provides valid
attitude, angular rate and acceleration information to the GIA 63W Integrated Avionics and the
GDU 1040 Primary Flight Display.
An Attitude and Heading Reference System combines the functions of a Vertical Gyro and a Directional
Gyro to provide measurement of Roll, Pitch and Heading angles. The Garmin AHRS and magnetometer
replace traditional rotating mass instruments.
Using long-life solid-state sensing technology, the GRS 77 AHRS and GMU 44 Magnetometer combine
3-axis angular rate, linear acceleration and magnetic field measurements to create an electronically
stabilized AHRS.
The GRS 77 provides the following information in ARINC 429 format:
•
Aircraft heading, pitch and roll
•
Aircraft yaw, pitch and roll rates
•
Aircraft body-axis accelerations
•
Rates of change of heading, pitch and roll
•
Aircraft accelerations expressed in a local level frame of reference
The GMU 44 magnetometer provides magnetic information to support the function of the GRS 77.
The GRS 77 provides operating voltage to the GMU 44 Magnetometer.
The GRS 77/GMU 44 is capable of maneuvers through a range of 360° in bank and pitch. The rotation
rate capability is ±200° per second. However, ARINC 429 angular rate output messages are limited to
±128° per second.
Bank error and pitch error are within ±1.25° over the range of 30° bank, left and right, and 15° pitch nose
up and nose down. Heading is accurate to within 2° in straight and level flight.
Operation is not authorized north of 70° North latitude nor south of 70° South latitude due to unsuitability
of the magnetic fields near the Earth's poles. In addition, operation is not authorized in the following two
regions:
G900X/G950 Installation and Maintenance Manual – GRS 77 and GMU 44
190-00719-00
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Revision D