TA/RA

[alexmambo]

Hi guys,as far as you know,is it possible this situation? 2 aircrafts in proximity,one recieves a TA and the other one recieves RA? one is climbing from 340 to 360,passing through 343 recieves TA,the other traffic level flight at 350, 6NM.Thanks for your answers.

[Mad (Flt) Scientist]

I think I can think of a circumstance: the a/c at FL350 is at the altitude above which climb or increase climb RA are inhibited, for performance reasons.

In that case, if we assume a cooperative scenario, the climbing aircraft will I believe be told to stop climbing (via an RA) and the FL350 aircraft will just hold, which may just mean a TA since no action is required? Because the only RAs that can be issued for the higher a/c are descend cases, which dont help resolve the conflict.

[alexmambo]

well,maybe I was not clear,we were climbing,as instructed by the atc,and we`ve got a TA, but the other traffic complained to atc that they`ve got a RA. The moment ATC realised a potential conflict said our callsign ....maintain for a while...ughhh.We`ve stopped climbing,had a TA alert,then the other traffic passed over but 6 miles to the south and 4-500ft above,and they`ve been complaining to the ATC that they had RA.As far as I know we were supposed to have a RA as well,but maybe the other pilot wasn`t clear about the phraseology and TA/RA meaning.So my question actually is,shouldn`t both a/c involved in a conflict recieve RA,or TA?or one can get a RA and the other a TA? Thanks

[Checkboard]

Are you sure about your terminology? What exactly did the box say?

"Traffic, Traffic", or something like:
"Monitor Vertical Speed"

[fellman]

The climb inhibit is not a factor. This does not inhibit RAs. An RA will still be generated if required but it will be a "don't climb" or a "descend" RA.

[fellman]

It is perfectly possible for one aircraft to get only a TA while the other gets an RA. A common mechanism by which this occurs is the operation of the horizontal Miss Distance Filter in TCAS version 7.
If TCAS can reliably determine that there will be significant lateral separation then any RA that would otherwise be generated is suppressed. However if the the TCAS surveillance happens to be "noisy" then the determination is not reliable and so the RA is issued.
It is often the case that the MDF on one aircraft's TCAS suppresses an RA on that aircraft while the MDF on the other aircraft's TCAS does not supopress the RA on that aircraft.

[lion-g]

I have encountered this situation before, my aircraft being in a steeping descent than the aircraft above .... What I have gotten is an amber square on my ND, with "Traffic, Traffic" aural warning.

The other aircraft in fact encountered a TCAS RA ! He was "forced" to carry out a TCAS CLB. He was not suppose to descend until we pass his descent path but he did anyway.

[alexmambo]

Thanks a lot guys for your answers,and Checkboard,yeah right,thanks for confidence.

[Ocampo]

Maybe the mode in which the TCAS was set has something to do with the alerts it generates? I've heard of some airlines that select BELOW mode in cruise.

[fellman]

No - selecting "above" or "below" makes no difference to RAs. It merely determines which aircraft are displayed on the traffic display. The aircraft that are not displayed are still tracked by TCAS and RAs will still be generated against these aircraft if required (and those aircraft will be displayed as a red square whichever display mode is selected).

[Maurice Chavez]

I think I can think of a circumstance: the a/c at FL350 is at the altitude above which climb or increase climb RA are inhibited, for performance reasons.So then a DC-8 and and a 737NG have programmable TCAS then, based upon aircraft performance.....Interesting.... :8

[lion-g]

Hi Guys,

Just to revisit this thread. Recently I heard that it's impossible to get a TA with a conflicting traffic getting an RA.

When a TA occurs with a conflicting traffic getting an RA, I was told that it was due to the interrogation rate was not "fast enough" and it keep recalculating based on the our instantaeous V/S, which we are changing, thus only "able to render" a TA on our side.
(The arguement was that both A/C having the same envelope will definitely get a similar Resolution.)

Apperently, when a TA occurs, we are not suppose to make any changes to the vertical plane so that we can allow the TCAS to do the calculation.
Sounds logical if there's more than 1 conflicting traffic.

Anyone have got more information about TCAS system ? Especially on horizontal Miss Distance Filter in TCAS ?

Thank you in advance.

Cheers,
lion-g

[RAT 5]

Apperently, when a TA occurs, we are not suppose to make any changes to the vertical plane so that we can allow the TCAS to do the calculation.
Sounds logical if there's more than 1 conflicting traffic.

That's an interesting one. Does everyone do this? I can think of many occasions where doing something after a TA is a good idea to avoid an RA: e.g. a steep climb or descent. You see the TA, maybe the TFC even before a TA; note its reletive level and clb or desc profile, and adjust yoiur profile accordingly. Is this not common conflict preventation airmanship?

[jimbo804]

Limit rate of descent to 1500 fpm within 2000' of levelling off.
If TA triggered prob to late.

TA alert
SOPs should take over
PF directs PNF to conflicting traffic whilst preparing to 'correctly' respond to the impending RA.

Never assume the traffic out the window is actually the conflicting traffic!