View Full Version : A320 Mode S

22nd Jan 2010, 15:50
For the airbus experts

If the transponder is left in Auto after parking, does the mode S keep on transmitting non-stop?

FCOM 1 is not specific about this issue, and every pilot has a different opinion.

some say: live it in Auto, it's not an issue!
some others: put it on SBY because mode S is transmitting!

not to confuse with the other modes which are connected to the nose gear or air/ground logic.

Dan Winterland
22nd Jan 2010, 16:12
IIRC, it starts transmitting as soon as the ATSU detects you have departed and stops when it detects you have blocked on. We leave ours in Auto all the time.

This is confirmed by the fact that when we had 3 knots as the parameter for the recording of the Out time, we used to get ATC asking us to switch the transponder on if it was a slow push. Now we use the park brake off as the parameter, we don't get the ATC requests.

beam app
23rd Jan 2010, 08:51
Transponder transmits upon ground request, see ATC 1.34.50.P1
Take care

23rd Jan 2010, 15:06
some say: live it in Auto, it's not an issue!
some others: put it on SBY because mode S is transmitting!

What matters is what FCOM 3 says in PARKING procedure. Every pilot's different opinion is irrelevant.

24th Jan 2010, 13:09
SET on STBY, according to FCOM 3, or QRH.

But I have always found it in AUTO every time I get to the airplane.

25th Jan 2010, 16:36
thanks guys

Dan, according to that, there's no need to move it from auto if its linked to the ATSU block. though our S.O.P. was recently amended to set it on sby on parking.

out of curiosity I will place the following question.

Is the latest A320 ATCRBS Mode S available to the controller, when the ATSU has blocked off?


27th Jan 2010, 13:03
What about airports like LHR where the local rules specify that "After parking, the Mode A code 2000 must be set before selecting OFF or SBY."

Assuming (the documentation is really vague on this, as already mentioned) the A320 transponder goes automatically to SBY at "ATSU in" or parking brake/engine shutdown/whatever, does it make a difference to LHR ATC whether you enter 2000 before that event or afterwards? ("before" requires to change the code when approaching the gate, which is probably not the best time to play with the transponder).

27th Jan 2010, 13:19
I dont understand the question when you refer to mode S.
Is it as a medium or as transponder transmitting code (using mode S) when on the ground...

27th Jan 2010, 13:39
The A320 mode A switches off at nose gear touchdown, as we keep the knob in auto mode, but mode S is still transmitting after landing and taxiing, but does it stop when the ATSU blocks on? this is what is suggested by Dan.
I don't know were I can find something writen about it.

27th Jan 2010, 13:53
Mode S is also used by ADS and is entended to be used on the ground on different applications, for taxy runway incursion protection ....
so my guess is that mode S is available and used when an applcation (such as ADS) requires it

beam app
29th Jan 2010, 14:50
My Dear ,
The S MODE is not transmitting, is just RESPONDING, answer to an interrogation from the ground radar.