MODE S on the ground

[TOPBUG]

Gentlemen a question - should alt reporting (mode C) be selected with a Mode S transponder when using it on the ground (eg LHR and CDG). Please give me the answer to this to stop endless discussions in the flightdeck! Jepps/Aerads are unclear on this

[ElNino]

I always leave Alt reporting on, thus minimising the risk of forgetting to switch it on prior to take-off. Which has happened and leads to red faces at the very least.
In CDG, the controllers will often tell you to "squawk mode charlie"

[mupepe]

Hello!
in our aircrafts we select the txp. through RMU's and set
"ATC ON ", which replies on mode S and A , no altitude reporting.
Other option is "ATC ALT" which replies on mode A , C and S, with altitude reporting but useless on ground!
Controlers in Paris do ask to set the mode C in order to tell you to run the txp and get the mode S ...not knowing the kind of set up you have to perform to engage mode S.
happy easter!

[RaRadar]

Any Mode S ATC radars around the airport will still track Mode S targets on the ground. If you leave ALT selected it allows the radar (or any display system) to discard the data if it is not wanted.

RR

[TOPBUG]

Fine - but what do ATC want? Can any controllers give me the answer?

[Gonzo]

I don't think it matters, as RaRadar says, if altitude is selected, our gear filters it out if you're on the ground.

[Phoenix_X]

And if they filter it out, they don't need it , so that can probably answer your question .

[v1rotate]

I tend to set the Transponder on mode A, the problem is that when you have to taxi to the threshold at say 09L at Paris and that is the only runway they are using, aircraft on approach will have a cluttered screen indicating everyone holding at the threshold.

It doesn't matter to ATC but may make a difference to the other aircraft on approach.