TA/RA > ALT ON : ATC Question

[Mr Falcon]

Hi ATC

Please can you confirm what difference you see on your screen if an aircraft has transponder with ALT ON or TA/RA ? Am I correct in thinking that ALT ON the TA/RA is suppressed but modes A,C,S are all operating the same in both modes ?

We now have ALT ON on our checklists from taxi to runway and runway to stand.

Thanks.

[Roadrunner Once]

Not what you asked, but in the UK, the CAA has decreed that TCAS downlink information shall not be displayed on the surveillance display, so no difference here.

[Pringle_]

At our unit we receive a flashing notification of an RA and then (hopefully) a COC.

[CharlieJuliet]

AFAIK you select TA when you have a problem (such as an engine failure), and this tells other TCAS equipped aircraft that you will not (cannot) manoeuvre if an RA situation occurs. Thus the other aircraft knows it has to do all the avoiding.

[CharlieJuliet]

http://www.faa.gov/documentLibrary/media/Advisory_Circular/TCAS%20II%20V7.1%20Intro%20booklet.pdf
Try page 12 which says that TA ONLY will not issue an RA

[737aviator]

Hmm, we use ALT OFF from just before start request till cleared to enter the runway before departure and from runway to stand on arrival for identification at airports that have surface radar.
Why do you have to use ALT ON - what's the point of Mode C altitude returns when you're taxiing? :}

[MarkerInbound]

But I still don't know how you get from a technical system description to the operational procedure 'you select TA when you have a problem (such as an engine failure), and this tells other TCAS equipped aircraft that you will not (cannot) manoeuvre if an RA situation occurs.


That comes in the checklist for any situation that leads to shutting down an engine:

4 Transponder mode selector . . . . . . TA or TA ONLY

[737aviator]

Is it the same for something requiring a rapid (and maybe uncleared) descent or if you have limited manoeuvrability?

TA Only for an emergency descent to avoid RAs. The other A/C should still create a RA if necessary.

[bekolblockage]

Why do you have to use ALT ON - what's the point of Mode C altitude returns when you're taxiing?

Well its standard practice here.

Radar targets taxying around the airport are filtered out below 300 ft to avoid clutter.
Transponder is required to be on to enable A-SMGCS to operate but without Mode C the altitude is unknown and therefore not filtered, causing nuisance targets.

Don't know enough about TCAS to comment on the TA/RA thing.

At our unit we receive a flashing notification of an RA and then (hopefully) a COC.

Interesting Pringle_.
How is that downlinked? Via Mode S?
Was that function always there or only after Uberlingen?

[winchman41]

Was that function always there or only after Uberlingen?If there is any ACC/UAC around that is actually downlinking RA/TAs then this must be a fairly recent development. I know that guys in Maastricht UAC have been working on implementing such a feature, but whether this has been achieved by now or not is not known to me a this time. Anyway such technology is, if at all, only available since short and certainly not at or before the Überlingen mid-air.