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TCAS RA

Old 14th Dec 2016, 13:44
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TCAS RA

One aircraft is cruising at FL 310. A reciprocal traffic at FL 320 starts descending. Is it possible the descending traffic experienced RA and the cruising traffic only TFC advisory? I mean and the cruising traffic should have RA. Or not?
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Old 14th Dec 2016, 16:54
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It depends on logic of the RA and closure rate. Difficult to say who gets what. You just do as it says.
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Old 15th Dec 2016, 03:04
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Is it possible the descending traffic experienced RA and the cruising traffic only TFC advisory? I mean and the cruising traffic should have RA. Or not?
In most cases, only one of the conflicting aircraft will receive an RA.

That's because the shape of the RA protection area is highly elongated (it's not a circle) so it is possible that an RA will be triggered in one aircraft but not (yet) in the other. Chances are, the aircraft first receiving the RA will respond to it, such that the other aircraft never gets an RA.
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Old 15th Dec 2016, 09:34
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Also, it may depend on the setting in the individual aircraft. If Your TCAS is set to TA Only (as recommended in some books for final approaches to parallel runways), this might alter the TCAS callouts a bit.
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Old 15th Dec 2016, 11:15
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Also depends on the inhibits. Some aircraft have a max alt above which no RA or no climb RA will be given.
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Old 15th Dec 2016, 16:57
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That's a nice one in the sim. They gave us a climb RA while operating at maximum altitude. You have to follow the RA.
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Old 15th Dec 2016, 20:22
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I am surprised to hear that only one airplane would get the RA. My understanding is that the RA is coordinated (if both aircraft are so equipped) to ensure no further conflict - even if no maneuver is required - the RA command is keep doing what you're doing - still an
ra.
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Old 15th Dec 2016, 20:57
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I am with GlobalNav on this one. If one aircraft gets an RA, I thought the other one does too. As long as one aircraft not in TA of course
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Old 16th Dec 2016, 15:27
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Toseg: Absolutely yes, in your particular scenario.

Eversince introduction of TCAS ver 7.0 for RVSM implementation, a modified logic is embedded to reduce nuisance, high V/S level-off encounters.

If such is the case, the onset of RA being triggered for the aircraft maintaining level flight is delayed by 10 seconds. This applies to "time to CPA(*)" algorithm.

Feel free to PM me for authoritative reference, though I only have one for 7,0 that has been superseeded since.


* = closest point of approach

Hi, peekay4 you are suprisingly off here, I am afraid. Comapred to your standards, that is . You cannot hit one aircraft into another without including the second one in the collision, right?[/I]
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Old 17th Dec 2016, 02:31
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TARA

Dear colleagues the scenario is true. I had the traffic advisory and the other aircraft reported that he had resolution, but i am a bit reluctant to believe it. My transponder was in TARA mode.For this reason my question.This happened in Beira airspace. I had permission from Maputo to divert up to 40 miles right off track due to weather. After Maputo i changed to Beira and i reported that i divert right off track up to 40 miles. I was approximately 30 miles right off track.He acknowledged and he said to report abeam a point named AXIBO. After few minutes suddenly presented on the ND the traffic at FL 320 starting descent and we did not remember to hear any descent clearance from Beira. It was a Mozambique flight . He passed through our FL and very closed . To be honest i don't remember how closed he was and as i told before we had only TFC advisory. He reported RA and after this, he started to speak in Portuguese with Beira. We didn't understand what they said . The one i did not like at all was that i have been asked by Beira to confirm if i was diverting right or left off track. He pretended that he did not remember . Any way in Beira there is no any radar coverage so is very risky to accept directs or divert for weather. I have done the ASR but i have not received any answer yet. Does any body know if Beira will give the recordings? I don't think so

Last edited by toseg; 17th Dec 2016 at 02:56.
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Old 17th Dec 2016, 08:21
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The whole point of the system is to ensure the instructions are mutually relevant. No point in giving one guy one instruction and another nothing. That defeats the purpose of the system. Unless we are talking about being on the cusp of the cone in which the system changed its mind half way, but you say you were quite close.

Last edited by MonarchOrBust; 17th Dec 2016 at 08:31.
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Old 17th Dec 2016, 17:43
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It depends on the situation.
I was in level flight and had a KLM descend towards our level.
He got a TCAS RA, (level off order is my guess) and we got a TA. Had he continued his descent we would have gotten a TCAS RA, but there was no need for that as he leveled off.
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Old 22nd Dec 2016, 20:00
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You might get a "Monotor Vertical Speed" and the VSI green band being 0 fpm. Its still an RA though, and you must comply with it. ( Disclaimer:-my Company Ops, and type)
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Old 22nd Dec 2016, 21:47
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MadaAdaSystem: exactly as per design, and your understanding is 100% on target.
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Old 22nd Dec 2016, 22:06
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Hi, peekay4 you are suprisingly off here, I am afraid. Comapred to your standards, that is . You cannot hit one aircraft into another without including the second one in the collision, right?
FD, just saw the fine print.

No, I am not off, as both toseg and ManaAdaSystem have confirmed exactly what I wrote through their actual experiences.

As mentioned previously, it's not unusual at all for only one aircraft to receive an RA. In fact, it is the norm, due to the elongated shape of the protection area. TCAS II facilitates RA coordination between aircraft, but does not require both aircraft to receive RAs.

Here's a typical TCAS II protection area diagram (2D view):



Notice that the area is asymmetric front & back. Since the protection area is not a circle (sphere in 3D), one can easily construct a scenario where the intruder aircraft is within the other aircraft's RA zone, but not the other way around.

With TCAS II, the first aircraft that generates an RA will transmit its maneuvering intention (e.g., climb, descend) to the other aircraft, but this transmission in itself does not force an RA on the 2nd aircraft.

If (and only if) the 2nd aircraft also generates an RA some time later, the first aircraft's intention will be taken into account by the 2nd aircraft in issuing a coordinating RA, subject to whatever inhibits are active at that time.
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Old 10th Jun 2023, 14:16
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Dear all,

I was querying some information about TCAS RA and found that thread (sorry for coming back to a rather old discussion).

Last week, flying an A220 level at FL320 within German Airspace, we received a TCAS RA Descend order which we obviously followed promptly.
Once clear of conflict, we returned to FL320 and asked the ATC about the other aircraft.
It was apparently flying level as well at FL330, a northern-american B767 which reported no RA but also no TA.

We were quite surprised to ear that the conflicting traffic could have no RA or TA while we were manoeuvring away.
This thread suggests that it could be possible.

Anyone experienced something similar recently?

Thank you for your feed back.
Regards.
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Old 10th Jun 2023, 16:59
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Originally Posted by totolariko
Dear all,

I was querying some information about TCAS RA and found that thread (sorry for coming back to a rather old discussion).

Last week, flying an A220 level at FL320 within German Airspace, we received a TCAS RA Descend order which we obviously followed promptly.
Once clear of conflict, we returned to FL320 and asked the ATC about the other aircraft.
It was apparently flying level as well at FL330, a northern-american B767 which reported no RA but also no TA.

We were quite surprised to ear that the conflicting traffic could have no RA or TA while we were manoeuvring away.
This thread suggests that it could be possible.

Anyone experienced something similar recently?

Thank you for your feed back.
Regards.
I had an RA at FL300, other aircraft was assigned FL320, but inadvertently descended and maintained FL306. we saw him level at FL306 for a while, but due to frequency congestion could do nothing. First got TA, followed by RA to descend. We complied, and afterwards climbed back up to 300. Other traffic didn't climb. I have no info if they had TA or RA, but if they did, they didn't do anything about it.
In your case it seems to be a problem with your TCAS as with both of you at level with a 1000' between it should have given neither a TA nor an RA.
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