Flight Instrumentation; Gfc 700 Autopilot; Flight Director; Autopilot - Garmin CIRRUS PERSPECTIVE SR20 Line Maintenance Manual

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3.1 FLIGHT INSTRUMENTATION
The GRS 77 AHRS, GDC 74A Air Data Computer, and GMU 44 Magnetometer provide the system
with flight instrumentation data. The data consists of aircraft attitude, heading, altitude,
airspeed, vertical speed, and outside air temperature information, all displayed on the PFD (the
same data is displayed on the MFD in reversionary mode).
Data outputs from the GRS 77 and GDC 74A are sent directly to the PFD using ARINC 429.
Additional communications paths connect the GRS and GDC 74A to GIA 63W units providing
quadruple redundancy.
The GRS 77 receives GPS data from both GIAs, airspeed data from the GDC 74A, and magnetic
heading from the GMU. Using these three external sources, combined with internal sensor
data, the GRS accurately calculates aircraft attitude and heading (Figure 2‐1).
In addition to using internal sensors, the GRS 77 uses GPS information, magnetic field data, and
air data to assist in attitude/heading calculations. In normal mode, the GRS 77 relies upon GPS
and magnetic field measurements. If either of these external measurements is unavailable or
invalid, the GRS 77 uses air data information for attitude determination. Four GRS 77 modes of
operation are available and depend upon the combination of available sensor inputs. Loss of
air data, GPS, or magnetometer sensor inputs is communicated to the pilot by message
advisory alerts.
3.2 GFC 700 AUTOPILOT
The GFC 700 is a fail‐passive digital flight control system composed of multiple Garmin LRUs and
servos. The following functions are provided by the GFC 700 in a Perspective™ installation:
Flight Director
•
Autopilot
•
Pitch Trim
•
Yaw Damper (optional)
•
3.2.1 Flight Director
The Flight Directors operate within the GIA 63Ws and use data from the GARMIN system,
including air, attitude, and flight data, to calculate commands for display to the pilot and for the
Autopilot. Flight director command bars and mode annunciations are sent to the PFDs through
a high‐speed Ethernet connection for display to the pilot and copilot. The flight director
operates independently of the autopilot and allows the pilot to hand‐fly the command bars if
desired.
3.2.2 Autopilot
The autopilot operates within two GSA 81 servos (pitch and roll). Flight director data is
processed within the servos and turned into aircraft flight control surface commands. The
autopilot cannot operate unless the flight director is engaged.
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Rev. E
Cirrus Perspective™ Line Maintenance Manual
190-00920-00