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Altitude Encoding

Postby JimB » Tue Jul 18, 2017 6:57 pm

I have had my Sport HS EFIS providing altitude information to my GNS430 and GTX327 using the Fuel/Air Data Z Format for many years.

I have now replaced the GTX327 with an Appareo ESG transponder. It does not accept the Fuel/Air Data Z Format. I found that if I use the Trimble/Garmin encoding altimeter output of my EFIS, the ESG will function correctly. However that required that I change the altitude input format on my GNS430 to Icarus-alt. (the wiring from the EFIS splits to the GNS430 and the transponder).

I think the GTX327 needed air data to obtain GPS information primarily to know when the aircraft is in motion to switch from STBY to ALT mode. Since the ESG has a built in GPS, all it needs is altitude data. I think the same can be said of the GNS430, it only needs altitude data and not GPS or pitot airspeed data.

I think this is OK but would like confirmation.


Jim Butcher
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Joined: Tue Mar 12, 2013 12:52 am

Re: Altitude Encoding

Postby GRT_Jeff » Wed Jul 19, 2017 1:02 am

The GNS430 can use the airspeed, wind, and fuel information in the Fuel/Air Data message, mainly for flight planning and display. The airspeed information is also provided in the ARINC-429 connection.

Note you can use the "Serial--trim/gar-25 ft" (higher resolution) setting in the Stratus.
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Joined: Tue Dec 11, 2012 12:11 am

Re: Altitude Encoding

Postby Bobturner » Wed Jul 19, 2017 4:53 am

Small note: As of a few years ago the FAA recommended procedure is to turn auto-switching off; run the transponder in ALT mode whenever the engine is on.
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Re: Altitude Encoding

Postby JimB » Wed Jul 19, 2017 3:19 pm

Thanks Jeff and Bob. It looks like I will be fine as I have it configured.

This information would be useful in the GRT Equipment Supplements document. I had no idea that my GRT would have the accuracy to use the higher resolution setting in the ESG.

Jim Butcher
Posts: 76
Joined: Tue Mar 12, 2013 12:52 am

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