Transponder Ground Mode Gone

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gordsh
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Transponder Ground Mode Gone

Post by gordsh »

Ever since installation of the GTX345 for ADS-B upgrade I noticed that I can no longer access "Ground" mode on the G1000's Transponder. Before this upgrade while on the ground, I would engage Ground Mode and the G1000 would automatically switch to ALT/VFR mode on take off. Similarly, on touchdown it would automatically switch to Ground mode.

With the installation of the GTX345 this feature is now gone (at least with the legacy G1000). I contacted the factory and they have conformed that this by design. Now, when ever I engage Ground mode I get an alert 'XPNDR GND UNAVL - XPNDR mode not supported. See AFMS'.

Here is the Garmin document explaining this in case some one else has this problem.
GTX 355R with Legacy G1000.pdf
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Rich
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Re: Transponder Ground Mode Gone

Post by Rich »

I believe this is a big deal and that Ground Mode is a specifically required behavior in ADS-B land. It's to transmit a specific message structure. In my KT74 installation, an airspeed-based squat switch was required as part of the installation and it automatically switches.

With my 327, ground mode wasn't really a thing. It went between standby and ALT based on groundspeed.

Maybe it's a terminology conflict?
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gordsh
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Re: Transponder Ground Mode Gone

Post by gordsh »

Rich, I spent some more time today researching this and from what I can find in GARMIN docs 'ALT' mode now replaces 'GND' mode. That is whether on the ground or in the air the 'ALT' mode should be selected and the GTX 345 will determine what to transmit on its own.
2018-08-31_21-55-45.png
So I guess 'ALT' it is from now on unless otherwise instructed by ATC.
Last edited by gordsh on Sat Sep 01, 2018 2:02 am, edited 1 time in total.
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Rich
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Re: Transponder Ground Mode Gone

Post by Rich »

gordsh wrote:Rich, I spent some more time today researching this and from what I can find in GARMIN docs 'ALT' mode now replaces 'GND' mode. That is whether on the ground or in the air the 'ALT' mode should be selected and the GTX 345 will determine what to transmit on its own.

2018-08-31_21-55-45.png
That makes perfect sense.
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rdrobson
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Re: Transponder Ground Mode Gone

Post by rdrobson »

Rich wrote: Sat Sep 01, 2018 2:02 am
gordsh wrote:Rich, I spent some more time today researching this and from what I can find in GARMIN docs 'ALT' mode now replaces 'GND' mode. That is whether on the ground or in the air the 'ALT' mode should be selected and the GTX 345 will determine what to transmit on its own.

2018-08-31_21-55-45.png
That makes perfect sense.
I can confirm that this works as advertised in real life. I flew in and out of John Wayne (KSNA) this week where ground transponder use is mandatory. I didn't do anything different than what I always do with regard to transponder use and everything worked fine. I noticed that it was flashing the little 'R' while on the ground. Also, I heard ground control admonishing other pilots for not having their transponders in the correct mode.

--Ron
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Lance Murray
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Re: Transponder Ground Mode Gone

Post by Lance Murray »

Transponders are now supposed to be in Alt mode for all movement operations on the ground.

https://www.faa.gov/other_visit/aviatio ... O15006.pdf
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Rich
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Re: Transponder Ground Mode Gone

Post by Rich »

FAA AC 20-165B has a clearer discussion on this matter and others. For example, stuff to be transmitted in GND mode and not in flight. Also various descriptions on recommended methods of automatically switching modes.

I couldn't get a link that would work and the file is a bit large to attach here, but you can look it up.

https://www.faa.gov/documentLibrary/med ... 0-165B.pdf
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