photoInstallation Secrets:
GPSS Inhibit Using the GPS Annunciate Output of the Garmin 430/530

Butch Nimmo
Tech. Rep.


Many of you have expressed a desire to be able to inhibit GPSS operation when VLOC is selected on the Garmin 430/530. This article will tell you how to wire that option. This may require that a deviation be granted by the FAA to the original wiring provided by the STC.

System FiftyFiveX
P/N 01192 - ( ) -( )

All System FiftyFiveX cable harnesses assemblies are shipped with the GPSS enable jumper in place across P2 Pin 38 and Pin 43. Remove the jumper between P2 Pin 38 and P2 Pin 43. Configure per Figure 1 below.


ST-901 GPSS Converter
P/N 03976 SN xxxx Code "A" and Later

The ST-901 GPSS Converter has a GPSS override feature that can be used for GPSS inhibit. GPSS inhibit can be accomplished by adding a diode and jumper between the Garmin 430/530 and the ST-901 GPSS converter as shown in Figure 2 below.

In either of the above scenarios, selection of VLOC on the Garmin 430/530 front panel will inhibit GPSS operation. If the system FiftyFiveX is in GPSS mode when VLOC is selected the "GPSS" and "NAV" annunciators begin to flash and the "Fail" annunciator is on steady. The GPSS roll steering output reverts to a wings-level command. If the system FiftyFiveX is not in the GPSS mode, any attempt to activate the GPSS mode will not be successful.

If the ST-901 is in the GPSS mode, the GPSS annunciator will begin to flash and the converter output will revert to a wings level command.



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