Turning Transponder to ALT in Runup?

Cris

Cris

flying bus driver
Debated with some others on this topic; my understanding is that it congests the controller's screen when you turn it on which is why I have always waited till taking the runway but I'm curious what controllers think about this.
 
I'd be curious about what controllers want to see at towered general aviation airports. In the airline world we always used to turn it to standby on the ground and then several larger airports wanted it on ALT. More recently my last airline and now my current have it written as operational policy to turn it to ALT after engine start and only back to STBY after engine shutdown. With older transponders in GA airplanes the selector knob is often the first thing to break so I would prefer to leave it in ALT but certainly not if it causes any issue for controllers.
 
hammerhat said:
There's been a change in AIM about 3 years ago. With that change FAA requested pilots to turn on Mode C prior to moving on the surface. 4-1-20
Click to expand...

There you have it.

There's only 1 aircraft at my airport who we routinely advise to leave it on standby, because his transponder manages to generate a radar return while he's still on the ramp and it complicates things with our flight plan/hand off software. I've only ever seen it with that 1 plane here, though.

We don't have ground radar (ASDE-X) anyway so it wouldn't bother us if pilots DID wait until run up/takeoff to turn it on. However, considering the new AIM guidance, you should just click it on when beginning taxi.
 
Ours always stay in ALT. Most satellite GA fields, including towered, don't have radar down to the surface so it usually takes a couple hundred feet before you "tag up" on the display anyway.
 
hammerhat said:
There's been a change in AIM about 3 years ago. With that change FAA requested pilots to turn on Mode C prior to moving on the surface. 4-1-20
Click to expand...

That's good to know. The place I was flight instructing at with the G1000 equipped aircraft had the transponder automatically turn on to ALT above a certain groundspeed 40 knots I believe it was. And once we slowed on arrival it would go back to standby. At the airports with ASDE-X I would always have to go in and turn the transponder back on. Sometimes we forgot, and ground would tell us.
 
Turning on the TXP on the ground was/is a problem with the old analog radars like the ASR 5,6,7 and only if your at an airport that has the radar site at the airport, its called " ring around". This is not a problem for the digitized radars like the ASR 8D.9 and 11. Only saw it once in my USAF days at RAF Bentwaters never saw it in the FFA.
 
JustinS said:
That's good to know. The place I was flight instructing at with the G1000 equipped aircraft had the transponder automatically turn on to ALT above a certain groundspeed 40 knots I believe it was. And once we slowed on arrival it would go back to standby. At the airports with ASDE-X I would always have to go in and turn the transponder back on. Sometimes we forgot, and ground would tell us.
Click to expand...
The Garmin ones if they are in gnd mode will reply to certain interrogations.
 
Cris said:
Debated with some others on this topic; my understanding is that it congests the controller's screen when you turn it on which is why I have always waited till taking the runway but I'm curious what controllers think about this.
Click to expand...

Turning the transponder on really only matters at airports that have the ASDE-X ground radar. Controllers at airports that don't have ASDE-X don't see your transponder when you turn it on while on the ground (generally.) The software that displays the radar targets on the scopes includes certain filters to keep false targets from showing up on our screens.
 
The 777 and 787 have a five position transponder selector switch. The positions are: STBY, ALT RPTG OFF, XPDR, TA ONLY, and TA/RA. The procedure is to turn it to XPDR prior to pushback at airports equipped to track airplanes on the ground then TA/RA when taking the active runway for takeoff. It goes back to STBY after landing and finally STBY after parking. Realistically speaking it goes to XPDR for every pushback.



TP
 
We can also adjust our filters so something on the ground that we don't need to see doesn't show up generally. Contrary to the other argument our filters are altitude based so without ALT on, an A/C on the ground will show up while one squawking ALT will not as the computer has the mode C and can filter it out based on the preferences.

Even at airports without ASDE-X, with RADAR depending on line of sight, I can see aircraft taxi out if there is an antenna close enough feeding returns. I managed to catch one on the wrong squawk at a non ASDE-X airport as they lined up on the runway and tower called for the release not long ago. With Fusion this is more common.
 
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