97-13 LRU Installation – GRS 77H AHRS
A. Description
The Garmin GRS 77H Attitude and Heading Reference System (AHRS) provides
aircraft attitude information to the G500H EFIS system. The GRS 77H interfaces
with both the GDC 74H Air Data Computer and the GMU 44 magnetometer. The
GRS 77H 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.
B. Schematic
Refer to Figure 98-11 for GRS 77H AHRS Installation electrical schematic.
C. Removal
1. Turn battery & avionics switches off and pull out EFIS (5 amp) circuit breaker on
circuit breaker panel.
2. Hinge left seat forward and remove F950-3 cover assembly.
3. Disconnect airframe harness from GRS 77H AHRS at connectors.
4. Loosen thumbscrews securing AHRS to F950-1 support assembly. Carefully
remove AHRS from under left seat.
D. Installation
1. Turn battery & avionics switches off and pull out EFIS (5 amp) circuit breaker on
circuit breaker panel.
2. Place GRS 77H AHRS on F950-1 support assembly and tighten thumbscrews.
Verify security.
3. Connect airframe harness to GRS 77H AHRS at connectors.
4. Push in EFIS circuit breaker (5 amp) on circuit breaker panel. Turn battery &
avionics switches on.
5. Perform appropriate functional checks per Garmin G500H Instructions for
Continued Airworthiness. Turn battery & avionics switches off.
6. Install F950-3 cover assembly and hinge left seat back.
APR 2019 Chapter 97 Avionics Page 97.3
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