Transponder at the gate
 

What powers the transponder that allows us not to select standby after engine shutdown. (Airbus, but might apply to Boeing too)

On the A330 and A340 and A350 nothing you select stby after engine shut down, electrics are still available.

that’s company policy. No need to select stby, transponder will stop broadcasting with engine shutdown. Fuel master?

Transponder in STBY NO transmission
Transponder in AUTO on ground Mode S only
Transponder in Auto in Flight Modes A C and S

Its NOT a company requirement but an ATC requirement to reduce traffic info on the ground, which is why it is set to auto with push / start clearance. Also a manufacturers SOP.

Do you have a reference for that? We leave it on AUTO all the time as well.

Our A320 FCOM:

Cockpit preparation
ATC ............................................................ ............................................................ ............. STBY
ATC and TCAS are on standby. To prevent possible interference to radar surveillance systems

At start clearance
ATC......................................................... ..........................................................SE T FOR OPERATION
ATC is set in accordance with airport requirements.

Parking
ATC......................................................... ............................................................ ...........................STBY


On the A380, we used to leave it on AUTO all the time. But that got changed to STBY at shut down as well. Something to do with Canadian ATC still seeing us on their screen I was told.

It still transmit even with engines shutdown. It happens to me a couple of times that ATC request us to put the transponder on STBY when we were at the gate. 99% of time ATC does not give a toss tho.
By Airbus SOP, transponder should be set on Stby at the gate and back on Auto when start up clearance is received.

Using an altitude filter, the label of the aircraft can be suppressed by setting a lower limit just above aerodrome elevation.

But in our case the system will throw a 0 on the mode C readout if it doesn't work for any reason, and that will then be corrected to a minus X amount of feet if the QNH is low..... so we never use the lower limit of a filtering function when working approach since we may loose the label if an aircraft has a mode C failure.

But for us with an "old" secondary surveillance radar having labels all over the airport can be slightly annoying for approach. But it all depends on the radar system... and I bet there are quite a few out there more advanced than ours :cool: