Transponder mode selector B744
 

Can someone please tell me why we have to wait until entering the active runway to select RA/TA?
I seem to recall t had something to do with cluttering the ground radar but can find no reference.
Thanks

Nothing to do with cluttering the ground radar. Only reason it has to be done is that they want to avoid a TA for landing aircraft.

Transponder suppression.
 

The transponder is suppressed on ground.
Most types are switched on/ off on nosewheel squat switch.

If you dont believe me watch the guy racing down the rwy on takeoff next time you are on short final!
You can see him but TCAS cant. And voila he lifts, and there he is.

Same on landing behind a fella: Now he is there, now he is gone, ie on the runway, no more mode A and C.

so the note on the FAA plans regarding ASDE-X is useless?
"ASDE-X in use. Operate transponders
with altitude reporting mode and ADS-B
(if equipped) enabled on all airport surfaces."
for example to find here:
http://aeronav.faa.gov/d-tpp/1803/00...nameddest=(JFK)

so it seems TCAS does the suppression because in mode-s on-ground is transmitted in the transponder response.

my guess would be switching ta/ra off means your TCAS isn't needlessly querying other transponders.

maybe this document can shed light on it ... https://www.eurocontrol.int/sites/de...t-20050403.pdf

I agree with you BluSdUp. The fact remains at least in my company is that the TA/RA mode is selected when cleared to line up. We are not 100% Boeing but I can not come to another conclussion than it would be a left over from the "old" days. Looking at the system there is no reason why you can not taxi around in TA/RA mode. As we do on the A330 but not on the B744 for some reason.

So I can not come to another conclussion that this a left over from the first days of TCAS

Unfortunately, sometimes aircraft transmit a continuous signal due some problem in the air/ground logic, which then in turn can give false TA/RA when aircraft is taxiing on ground to airborne aircraft.

e.g. on several occasions I have requested ATC to ask an aircraft on ground to switch off their transponder as I could see them on taxiway when on short final, when flying in IMC.

Boeing operator here (not on the B744)

Before starting the taxi-out we put the transponder in XPNDR, which basically sends signals to the ADS-B/Ground radar system. After vacating the runway, upon landing, we do the same. This mode shows a TCAS OFF message on my EHSI.
One airport in particular in our route network ask us not to do it, keep it STBDY, as their ground radar is an older generation and it would clutter the screens (or so I was told by an ATC chap).

When entering the runway, for departure, we select TA/RA, until vacating on arrival.

Now, en route, when asked to chance codes, most of the colleagues put it on STDBY, dial in the new code (or type it in, depending on transponder control panel type) and then back to TA/RA. I personally find this unnecessary and change the codes without selecting STDBY first.

Never, ever, go Stby in the air when putting in a new squack.

I did that on departure long time ago, had a rather close call!
Trust me on this one!
Not smart!
Tcas dont work and on Radar you vanish!!
( I had the wrong squack, that was what started it all, long story, short answer: NO stby in the air.)

High on my Top 10 never again list!!

So i found a definite reference by the FAA
https://www.faa.gov/other_visit/avia.../InFO11012.pdf

@coastrider26 so the FAA is not happy with your A330s :)

in the plates for EDDF you can find:

@coastrider26 so the FAA is not happy with your A330s :)

Luckily they were not operated to the US only to the far east and Oz. But Thank you for the reference, always thought it had to do with some older technology on the 744 vs A330 learned something new. Thanks for adding the reference as well.

Skyjob
Just read your reply.
Have had that as well, when stuff dont work , indeed it is a distraction and more.
Also had heli ops holding short with transponder on, Rather un nerving .

BluSdUp, my thoughts exactly :ok: