Troubleshooting The S-Tec 55X Interface; Interface Summary; Failure Modes - Garmin CIRRUS PERSPECTIVE SR20 Line Maintenance Manual

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5.17 Troubleshooting the S‐TEC 55x Interface
5.17.1 Interface Summary
• Autopilot computer is interfaced to GIA2 only
• Utilizes S‐TEC pitch servo and Cirrus pitch trim motor for vertical control
• Utilizes Cirrus roll trim motor only for lateral control
• Utilizes S‐TEC turn coordinator and S‐TEC altitude hold chamber
• Mode annunciation and FD are displayed on the PFD in normal mode and on the MFD if
the Perspective system is in reversionary mode
• Eaton switches on LH side of instrument panel annunciate "AP ON" (bottom half of
switch) and "AP OFF/FD ON" (top half of switch)
• GPS steering utilizes an ARINC 429 buss between GIA2 and the 55x
• Altitude preselect data utilizes an RS 485 buss between GIA2 and the 55x
• Analog outputs from GIA2 drive the GS deviation, GS flag, Nav deviation, Nav flag to the
55x
• Pitch and Roll analog steering outputs from the 55x drive the FD bar inputs to GIA2
which in turn are displayed on the PFD
• Clock, Sync and Data are used to transfer the mode annunciation information from the
55x to GIA2 which in turn is displayed on the PFD or MFD in reversionary mode
• DC course and heading datum outputs from GIA2 drive the 55x associated inputs
5.17.2 Failure Modes
• Loss of MFD or GIA2
o All mode annunciation removed from PFD
o FD bars removed from PFD
o S‐TEC computer remains in basic altitude hold (if selected prior to loss) and HDG
(if selected prior to loss) and is annunciated on the autopilot controller that way.
Keep in mind that because there is no longer any communication between the
autopilot computer and the Perspective system there is no way to input a
heading error to drive the autopilot.
• Loss of PFD
o No loss of autopilot functionality. Mode annunciation and FD transferred to MFD
in reversionary mode
Page 5-102
Rev. E
Cirrus Perspective™ Line Maintenance Manual
190-00920-00