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How do you operate/set up your transponder (on the ground)

This refers to whilst on the ground. Like many, I guess, I have once learned – back when transponders were still all manual – to set it to ALT when taking the runway and going back to STBY once clear of the runway. And never really changed habits.

However, more and more big airports (where, admittedly, most of us rarely fly) seem to start mandating the transponder to be on all the time.

On the Cirrus I fly, the GTX330 is set up in “automatic” mode, i.e. it switches to ALT when exceeding 30 knots.

On the Piper I fly, it is simply always on ALT. I was asking myself: does it do any harm? Seems the most sensible thing to do nowadays.

In practice, nobody (ground control, etc.) has ever told me to set it to STBY when it was on ALT. Also, nobody has ever told me to put it on ALT when it was on STBY…

Interested in any views.

Mainz (EDFZ), Germany

I set ALT when I start to taxi

EHLE / Lelystad, Netherlands, Netherlands

For the US, FAA issued a Safety Alert a while ago recommending that transponders in the US be set to ALT and left there at all times. As a result I rarely touch mine any more – its set to VFR and ALT and stays there.

Peter_Mundy wrote:

I set ALT when I start to taxi

Me too, although I seldom fly to really busy int. Airports. In central Europe there usually is a better (read: cheaper) small airfield in the vicinity of my destination..

Aufwind GmbH
EKPB, Germany

The automatic switch from Ground to Alt has been removed from the new generation of Garmin transponders, and the manual says

The transponder system no longer supports a pilot selectable GND mode. The transponder should always be in ALT mode prior to moving on the airport surface.

Last Edited by denopa at 14 Dec 19:21

I learned to set the transponder to Standby mode after switching on the avionics master after making sure the alternator is performing, allowing the (valve-equipped, at that time!) transponder to warm up. Then make sure to be in ALT mode before take-off. After landing, nothing really relevant. With today’s valveless aka solid state avionics, I am not sure the Standby mode has any “raison d’être” left, except for changing squawk. As regards the Ground mode, I never understood why it had to exist at all.

EBZH Kiewit, Belgium

My GTX330 is never touched.

It is on ALT all the time, and there is a differential pressure switch (pitot minus static) which switches it from GND to ALT when the IAS exceeds ~50kt. An earlier attempt to achieve this auto switching using GPS ground speed from the KLN94 failed to work despite it being shown in the GTX330 IM and the avionics shop charging me £500 for wiring it up There is some indication that a recent firmware update (mine is year 2005) fixes what they call “KLN89 issue” which I suspect may be a silent fix for this bug.

The automatic switch from Ground to Alt has been removed from the new generation of Garmin transponders

I wonder why they did that. The purpose of the GND mode is AIUI to work the same way as ALT but return a “ground” flag for the benefit of airport radar, and possibly to block it from affecting TCAS systems on nearby airborne aircraft.

Shoreham EGKA, United Kingdom

Previously in France it was mandatory to set it to the more sophisticated mode as soon as you started taxying.

Last Edited by Piotr_Szut at 14 Dec 20:08

Maybe something here?

Shoreham EGKA, United Kingdom

A couple of threads – albeit focussed on the US and that 2015 SAFO – are here and here. I still find the Garmin teminology and their changes to it a bit confusing…

Mainz (EDFZ), Germany
36 Posts
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