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GTX330 showing Mode A on TCAS

I came across one today. The aircraft type (not low end) was very suprising to be Mode A only, so after he landed I spoke to him and his transponder looked just like mine, showing ALT. We tested it on the ground and I still could not see any altitude return.

What config is needed to set a GTX330 to Mode A only? I presume it is Mode A+S in that case.

Administrator
Shoreham EGKA, United Kingdom

He might wish to check there is power to his altitude encoder or it may have gone tech. The GTX will still display ALT on the panel but the data will be absent in his reply to SSR.

Gloucester UK (EGBJ)

On the GTX330, press "On" to select mode A and mode S. Press "ALT" to select mode A, C, and S.

KUZA, United States

Hmmm - really interesting...

He said he will check it against the next radar service, so I guess he will get to the bottom of it.

It was a fairly close miss.

I am not so keen on Mode A only targets especially when in IMC and one of them is right at my position, like today... I asked ATC to fly the IAP at 4000ft (just above the cloud) instead of the 3200ft platform, due to the TCAS return.

Administrator
Shoreham EGKA, United Kingdom

On the GTX330, press "On" to select mode A and mode S. Press "ALT" to select mode A, C, and S

Would I be right in thinking then it sounds like it was switched on, but left in Standby? AFAIK (besides being powered on or off), the 2 operating modes are STBY and ALT.

If it has been configured correctly it should show GND and go to ALT when airborne without having to touch it.

Gloucester UK (EGBJ)

If it has been configured correctly it should show GND and go to ALT when airborne without having to touch it.

I wonder how many installs do switch automatically. I think a very small % does.

When I got the GTX330 installed in 2005, the installer wired it to the KLN94 for auto GS based switching. That is on page 74 in the IM. It never worked and both Garmin and Honeywell washed their hands of it. I paid a few hundred quid extra for that, but it was abandoned.

Only much later it was done, with a differential air pressure switch as described here. That works fine.

Administrator
Shoreham EGKA, United Kingdom

Only much later it was done, with a differential air pressure switch as described here. That works fine.

I have a pitot air pressure switch and it works great. It only cost me 100 € including install, one of the best investments I've made. Priceless when you takeoff into IMC with high workload and really don't want to put attention to why ATC cannot identify you.

If it has been configured correctly it should show GND and go to ALT when airborne without having to touch it.

Once I power on the radio's (by usage of a switch that powers all of them on, so not pressing the 'On' button on the GTX330), mine goes straight to STBY, and I am very sure (not 100%), that it will stay like that until I press 'ALT'. I havent seen GND or any automatic switching. Maybe it's to do with complexity of aircraft? Mine is in a PA28, with a GNS430, however the 2 are not linked, so I dont know if that has a bearing on the config.

From Garmin Installation manual:

"STBY Selects the standby mode. When in standby mode, the transponder does not reply to any interrogations. Pressing and holding the STBY key selects ground (GND) mode if Automated Airborne Determination is not otherwise selected from another source. When GND is annunciated, the transponder does not respond to ATCRBS interrogations but replies to All-Call interrogations."

Gloucester UK (EGBJ)
13 Posts
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