This rational action did not prevent the DHL Boeing from colliding.

For the Tupolev Crew: You forget, that they communicated with ATC for several seconds before they got the TCAS RA. They initiated the descend before TCAS issued its RA.

Your whole argumentation on rational action is biased by your western training. The Tupolev crew wasn't so "furtunate". In Russia the controlling of traffic is handled differently if you are an international flight that if you are a national flight. For national flights the controller has the authority to command the crew to take a certain action.

If you have followed this threat, you will see that a Ueberligen-like mid-air is still possible today, it sounds extremely simplicistic to present insufficiencies in the TCAS system as "obscure scenarios" of "conspiracy theorists".

What about this:


747 off of JFK full of fuel taking off into the NAT tracks, operating at maximum available cruising altitude for the moment at FL360, ATC asks if they're able FL 370 for traffic earlier, they are not able that level.

Now my question IF TCAS asked them to climb for an RA, is the airplane going to get up there? Also does TCAS take that into account or is it completely separate from those systems?

Since airplanes flying long haul are often operating near or at their maximum cruising altitude for their current weight, what if the RA tells them to climb and they cannot? Then what?

This is wonderful. You give us two different courses of action depending on whether there isn't an airplane where ATC says it is or whether there is.

Need I say it: if you have this trustworthy information, then you don't need either TCAS or ATC.

Let me show you a different way of thinking (I emphasise the word "thinking" :) ).

You paint an intruder at 10 o'clock. ATC gives you a descent for traffic at 2 o'clock. You don't descend (which would be against the RA).

BAM! In the few seconds of consciousness available to you, you might like to consider where your reasoning went wrong. Maybe it was because the likelihood is rather high that there is actually an airplane where ATC implies there is an airplane, even if your on-board kit doesn't see it; or maybe .... sorry, that's all folks.

I'll offer to write your epitaph. First proposal: "I've proved I'd do what I said I'd do".

PBL

Then they don't climb, and their "dance partner" is issued a Reverse RA.

At least, that is the thinking behind Reverse RAs. That it doesn't always work that way was proved at Überlingen.

PBL

This rational action(FOLLOWING THE RA) would have prevented the collision as the report obviously states.

I don't believe so. Read my previous post completely and carefully this time. In both scenarios I am not going to go against the RA's(as I have continuously stated on this thread) whether there is traffic at two o'clock or not. That is what I meant and that is what I said

You already have 71 epitaphs to write. No need to write my epitaph or anyone else's in this scenario because I would have FOLLOWED THE RA and ignored ATC once it was contradicted by the RA and I will do so in the future.

Why, because I have done my "thinking" before the flight even started and realized that Following the RA is the safest thing to do in a scenario like this, not trying to figure out the situation with little time available.

It is very true that the Russian system of training was at least partially at fault in this accident as has been mentioned in the report, however I was asked basically what I would do in this situation. Or maybe the captain listened to a couple of guys on an web site somewhere questioning the prudence of FOLLOWING THE RA.

More example of people who don't follow RA's or who try to out think a situation.

http://www.arinc.com/tcas/acasll_bulletins.html

There are situations where an aircraft is unable to comply fully with an RA due to performance limitations. The TCAS can be configured(not by the pilots) so that no climb RA will be given above a certain altitude for your aircraft which may or may not be your maximum certified altitude. When at a max altitude due to weight or in a low energy state or an non-normal configuration(gear/flaps that can't be retracted, etc) reacting fully to an RA can lead to stall warning. Use great care in such a situation to prevent an aircraft upset.

Thanks for those replies on my questions guys, really appreciate it.

I still find TCAS somewhat an imperfect system, if it can issue RA's when there's not an airplane near them, then I wonder if it will always issue the "right" direction.

I don't think the procedures should change, but something that must be taken into effect (that it's far from perfect)

We already knew that you would always follow an RA.

You were asked to show the error in the argument that the Baskirian crew's actions were rational, and how you arrived at your conclusion that it was not rational.


Bernd

Aside from the fact that they are all dead? Well, if you are flying in the mountains and ATC says descend immediately for traffic and moments later your GPWS goes off, which takes priority? If you are climbing slowly because you are heavy and ATC direct an immediate increase in climb due to conflicting traffic and moments later the stick shaker sounds, which takes priority? If you are in the situation over Germany that night and you have the conflicting messages that this crew had, which takes priority? There is only one rational answer to each, and in my opinion and none of them involve ATC taking priority.

But.....a previous post said that my action is biased by western training and that in Russia...."For national flights the controller has the authority to command the crew to take a certain action." It is a regulation to follow ATC instructions where I fly as well. Does that mean I am going to fly into the ground or stall the aircraft to follow an ATC instuction for immediate traffic separation? Do the Russian crews need to be told to ignore their stall warning or continue descending into the mountain peaks against their TAWS warning because of an ATC instruction?

P.S. I forgot to mention to the ATC poster that it is common to turn our transponder(TCAS) to TA only after an engine failure due to performance limitations. Also on parallel approaches to runways with less than 2500 foot spacing.

What would have been and what was are two completely different things. Fact is that the Boeing crew did behave just like you said you would. You said, that this would be the rational action. This must mean: following the rational course of action did not prevent the collision for the Boeing crew in the Ueberlingen case. The mid-air itself proves this.

Arguing about what-if is a completely different matter.

Had both aircraft followed the RA, the mid-air would have been prevented.
Had there only been the resolution issued by the Controller, the mid-air would have been prevented.
Had TCAS issued a reversal RA for the Boeing and Tupolev, the mid-air might have been prevented.
Had the STCA been available for the controller at ACC Zurich, the mid-air would have been prevented.

I could go on like this for pages ...

It would appear that you are going on. In the end, the vast majority of us follow the rational route and accidents are prevented. A few don't follow the rational route either intentionally or by mistake and only luck or chance prevents an accident as in the JAL case which I provided a link to and I'm sure you read. Most properly functioning systems and societies depend on the vast majority of us acting responsibly. Of course accidents and deaths occur frequently because of those who break the rules and occasionally to those who don't.

I hardly think that because the Boeing crew doing the proper procedure and dying because of it should mean that as a result we should all just stop following RA's and do something different on the off chance that the other guy may be not doing what should be done. After all that would be irrational(or lacking in LOGIC). As I said earlier it is an odds game with a much better chance of survival happening if you FOLLOW THE RA.

And fortunately people who behave like this(ignoring the RA) are few and far between, although there appear to be three on this thread. Strangely(according to their profiles), they all appear to be from Germany, two from near Bielefeld(the third an unknown German location) and two are aircraft accident analysts. One even has logic as an interest. What are the odds of that?

punkalouver,

bsieker and joernstu and I work together. They have put a considerable effort into analysing the Überlingen collision, amongst other accidents, so you are discussing with people who understand these situations very well.

Your recent postings support my earlier suggestion that you have not understood the decision problem. Here is the reason.

I suggested a consequence of your point of view, namely that you could be involved in a collision. You replied in a way that suggested that you think it is not possible under the conditions described (at least, that is what you say).

Well, such a view is obviously mistaken. It is obviously possible that you could collide in such a situation, even to people to whom TCAS is the best thing since sliced bread.

Let me attribute to you some insight, and assume you agree that it is possible that you might collide. Then you must think it is extremely unlikely. So in that case I would ask you to show your reasoning for this unlikelihood.

What you have said so far shows that you think it unlikely that you would ever come in such a situation. OK, but you were asked to judge, not the absolute probability of being in that situation, but the conditional probability *given the situation described*, for that is the judgement on which a rational decision is based. And the conditional likelihood can be a very different quantity.

For example, the absolute probability that I will be hit head-on by a car at a closing speed of over 30 kph while riding my bicycle is (I hope!) low. However, the conditional probability that I will be hit head-on by a car at a closing speed of 30 kph given the situation that a drunken driver has veered to my side of the road while going at 50 kph and I am 20 m from his front fender is rather high.

I think the very best you could do, if you wish to persuade people about the rationality of always following the RA, is to engage this and other decision problems that might be presented to you, and persuade those who are sceptical (such as I am, and bsieker and joernstu are) that following the RA is the best solution in each and every one of those situations. Personally, I doubt you can do that. But it may be well worth a try, to see where it succeeds and where it fails.

PBL

Unfortunately I don't have time to reply for the next few days. I don't think there is much more that I can say than has already been posted by myself already. I suggest that anyone reading this thread, read our posts for the last few days and decide for themselves what is best and why we are trained the way we are(and what the legalities are)instead of this thread going on
forever, basically saying with us all saying the same thing in a different way.

Perhaps I have misunderstood your whole arguement. I believe I did say that there is a risk of collision in the scenario that actually happened that night but that it is an odds game which I believe you agreed with. Following the RA reduces your chance of collision especially at high altitude on a dark night where VFR traffic is a non-issue and all aircraft are or should be under ATC control.

I have mentioned a disaster(over Europe), a near world's worst disaster(over Japan) and linked to a Eurocontrol newsletter that gives multiple examples of closer than necessary near misses due to not following the RA. That is in reality all I can do to prove my point. Perhaps you could prove yours by showing me some articles where lives were saved because the pilots ignored their RA. I suppose you will point out that the DHL pilots would be alive today if they had ignored the RA. But I don't think that is enough evidence for us to realistically consider doing this as a regular procedure or consider it at all.

All I can do is ask that everyone out there FOLLOW THE RA.

Thank YOU

OK, noted. Thanks for your contribution.

PBL

I can't remember advising anyone not to follow a RA, but surely you will prove me wrong? Following an RA you get may well be the best action for you, but as TCAS cannot solve every situation, you cannot be sure, that your action will save your life (and your passengers).

I cannot decide, what kind of action would induce the lowest risk - following an RA, not following an RA or flying without TCAS at all as the basis for my risk evaluation would be episodes. I think the same goes for you as your information basis is still only episodes.

Punkalouver :
This is new to me, and a bit surprising coming from you, as you referred to the Eurocontrol ACAS bulletins that has as first item in their do and don't list the following :
That aside , I find it a pity that you do not want to engage in the debate. The point many of us have ( and I am not working for or with PBL) is that the system is still far from perfect and even if you follow the rules , it will not protect you at all times. The GOL and DHL crew if they were still alive would sadly confirm this.

The sense reversal logic currently does not work and could induce a collision while trying to prevent one.

The interaction between human-ATC and automation -TCAS is still unclear for many , especially when ATC acts before the RA, and following the RA will mean acting against the current ATC clearance.

For those 2 reasons alone, following the RA is no guarantee that a collision will be prevented, because it needs 2 willing partners and you do not know what the other is doing.

Following your argumentation , would you be for the coupling of TCAS to the auto-pilot ? That would solve many problems wouldn't it ?

Concerning turning the transponder to TA after an engine failure...

Why are you surprised. This is our SOP and the SOP of many airlines if not most. Perhaps your training department felt it was not necessary to inform you of this.

Hmmm, I do see that you are from Germany as well. Anyways, I don't see the point of debating any more because I really have nothing more to add to what I have already said several times(Same with the others in my opinion). The thread is is just going on and on with myself and PBL and his coworkers(or aliases) repeating the same thing in different words. We have made our points.

You are absolutely right that you are not protected at all times, TCAS is not perfect and could induce a collision and I have never denied that. However the odds are in favour of you to FOLLOW THE RA.(See how I am repeating myself again).

The Gol accident involved non-functioning equipment on one the aircraft. I don't think it proved anything in terms of the whole TCAS design except what we already know; that won't provide any protection from an aircraft with no operating transponder whether a Piper Cub or a high level jet.

No opinion on autopilot coupling as I haven't heard arguements for and against this idea.

Fortunately for us, you are not flying an airliner and I suspect you would be demoted or worse if you followed through on this opinion in such a scenario.
bsieker(one of your like minded coworkers) in effect said so in my opinion in post #101 when he said the Tupolev crew's decision was rational which started this whole debate on the last two pages. And you strongly hint at it right after you ask me to prove you wrong by saying...

I cannot decide, what kind of action would induce the lowest risk - following an RA, not following an RA

Is there a website which currently lists all TCAS versions in use, their abilities (TA or RA, Climb only or turns) etc?

There are today only 2 TCAS in operations I and II.

TCAS I ,is a receiver that only gives TAs . description and users manual here : http://www.seaerospace.com/bfg/tcas791pg.pdf

TCAS II : the mandated system that issues TA and RAs in the vertical sense .
There are currently 2 software versions in use : 6.04A and 7.0 .
main differences > 7.0 is RVSM compliant and reduces the threat /sensitivity levels (margins ) to eliminate false alarms.
7.0 is meeting ICAO ACAS SARPS, 6.04A does not.
For a description and user manaul see here : https://www.bendixking.com/servlet/c...499-0000_7.pdf

The horizontal RA s ( i.e. turns ) was planned with a so called TCAS III but R&D on it was abandoned long ago, and it is very doubtful that they will restart.

Punkalouver :
I doubt this is the SOP of many airlines . Are you going to tell us that if you have an engine failure near Max Alt in dense continental airspace , and have to perform an emergency descent you are going to degrade your TCAS to TA only during he descent ?

I am not from Germany, but that does not constitute a burden is it ?

Most contributors here are from Germany perhaps because the critical knowledge is there : Lake Constance and the German BFU are located there and the University of Bielefeld has a chair on automation that is unique ( and they have for instance overturned many stones in the Airbus garden in the past).

I would have let it rest, but since you seem to have misread my post, I will explain it again.

Describing a course of action as a rational choice does not mean that it is the only choice, nor necessarily the only rational choice, nor necessarily the best choice, nor even that the actor(s) involved acted rationally when choosing that option.

The scenario which I described in more detail, in which following ATC was the only rational choice, is the scenario in which that crew did not receive an RA at all, because of inop TCAS.

The point being that all parties following their respective rational (in this case, even best) choices, one of which is following the RA, the other, in the absence of an RA, following ATC, (courses of action, I take it, you would approve) and yet they end up in a collision.

The problem is not so much following an RA, but the poorly-understood and unregulated (non-)interaction between TCAS and ATC.

This, as we have seen, may lead to collisions, although and because one crew follows its RA.

You say that you always follow the RA because the risk is lower than following ATC, where both are in conflict, but without giving even the hint of an argument for it, in the face of strong arguments (i. e. Ueberlingen) to the contrary. The Boeing pilot could not know if the Tupolev's TCAS was inop, or if they were just ignoring its RA.

If you misconstrue this as me generally recommending not following RAs, I cannot help it.

I am merely pointing to what I think is a big problem with collision avoidance in the larger system "air traffic", not looking at TCAS as an isolated system, but at the larger socio-technical system, comprising (at least) of two or more TCAS systems, two or more flight crews, several air traffic controllers, primary and secondary radar systems, ATC software, ...


Bernd

Concerning going to TA after an engine failure....

Yes I did refer to the ACAS Bulletins. They need to be read and understood completely though. Here is a link and quote from ACAS Bulletin 5, page 3, in the yellow box on the left side. The use of the TA-only mode is now limited to aircraft specific procedures, e.g. engine failure.

http://www.scribd.com/doc/351323/ACAS-Bulletins-5

If I have an engine failure near max altitude in "dense continental airspace" it will be more likely a driftdown not an emergency descent. And yes, as per SOP I will place the TCAs in TA mode when we get to it in the checklist just like we always do in the simulator. Just like I believe most other airliners will do.
No burden. I just foud it strange that all the people who seemed to disagree with me were from a country that has as a guess by me, perhaps 5% of posters on this forum. Of course I discovered that they all are from the same office. Just curious that's all. Here is why I thought you were from the same country and I quote.....Based in Europe( Germany) I have to go in Australia shortly and wants to take the familly with me... from this thread.

http://www.pprune.org/forums/showthread.php?t=281165

Sorry for the mistake on where you are from.

Some of the hints of arguement that I have given several times are the collision in Germany and near collision in Japan due to not following the RA.
Seeing as you and your colleagues, perhaps legitimately feel that there are occasional scenarios that TCAS can't resolve safely, perhaps you could give some interim guidance for pilots on what they should do if a similar situation is encountered as the Tupolev crew. My advice is to Follow the RA. What is your advice.

You are still unable to give a plausible argument, supporting your assumption, that following TCAS induces the lowest risk. If this would be the case - ask your superiors to copple TCAS directly to your autopilot system.

Thanks for proving, that your previous post was generalising and inacurate.

I want to remind you, that the argument in the lastest past was initated by you saying, that the Tu154 crews action were unrational. You have done little to support this allegation.

As if I'm going to walk into my head office and ask for a system to be modified(however much that costs) when there almost certainly isn't any approved modifications available on the market for this. There is a big difference between theory and reality.
I'm not going to respond to this as there is nothing to add to what I have already said. Instead I will leave your theoretical world of obscure possibilities and make a real world statement to all who fly with TCAS and could very well end up in the same situation as the Tupolev or JAL crew. Both had their reasons for ignoring the RA. One crew killed many while the other crew almost did. So please do as you have been trained. Do what Eurocontrol and the FAA and all regulatory authorities consider to be a RATIONAL reaction in such a situation. That is FOLLOW THE RA in spite of what ATC says.

punkalouver,

I thought you were bowing out of discussion because you had said everything you had to say? At least, that is what you said.

Having done that, I think it quite appropriate for others to summarise the issues you have addressed and the issues you have not addressed.

I also think it appropriate for others to correct your misrepresentations of their positions.

I see two different goals in this discussion.
Yours: you wish to derive advice to pilots from your understanding of TCAS
Mine (and that of, if I may anticipate, joernstu, bsieker and ATC Watcher): I wish to understand the technical workings and weaknesses of the TCAS system. And by that I mean not only the kit, which is nothing but an information device, but the entire collision-avoidance system, which can be considered to include pilots and airspace, regulations and controllers.

Somehow, you seem to think that I (and others) are attempting to derive advice to pilots. I, on the other hand, thought you were attempting to understand the technical workings of the system. That is, each thought the other shared a goal with him. I no longer think that is the case.

PBL

I agree. However, when one of your group(who's profile says accident analyst) goes on a widely read pilot forum and says that doing what the Tupolev crew did was a rational choice, it could easily be interpreted by some readers as advice even if it wasn't meant that way.

Perhaps you should say that you have "discovered or are aware of certain very rare occasions where following a TCAS RA could create a secondary conflict, however, in the vast majority of cases, all pilots following the RA including the 154/757 situation will prevent a collision."

Meanwhile I think some learning of the whole system has been accomplished on this thread about procedures such as when TA is selected and links to safety reports and newsletters and questions asked by others so this has been a useful thread. Glad to have been of help.

Which is why I went to some length to explain what I meant by rational choice.

And I also modified the setup so that the "Tupolev" crew did not receive an RA, but only ATC instructions, to which scenario you failed to make any statement whatsoever. I assume because you then would have to realise that all pilots following their, even in hindsight, best (as opposed to merely one of several rational) choice, could induce a collision.

And how do we know that it is indeed "the vast majority"? As long as we don't know that, we would not make a statement like that. Indeed, without the extensive data mining I mentioned before of air traffic data of a significant time period we cannot know.


Bernd

No more replies to obscure theory. You have the last word.

ATC Watcher wrote
Can you please expand on those problems induced by downlinking TCAS RA.

Songbird 29 :
The problems are numerous and complex and would vary depending on the medium used to down link the RA.
But as many believe that Mode S is the the only cost effective way to downlink RAs,. so let's take Mode S :

A recent QinetiQ study show that the average delay for controllers to be aware of an RA via Mode S is about 9 seconds and to get a verbal report from a pilot after an RA is currently about 29 seconds.
The main problem is what happens during those 20 seconds.

According to the current ICAO documentation the controller is still responsible and could/should issue instructions as long as the aircraft /pilot do not manoeuvre. The chances to have controllers intervene in those 20 seconds is higher than without RA downlink.
Next is the problem of intermittent short false RAs transmitted on mode S ( and that are down linked today ) but that are not resulting in an RA in the cockpit.

Lastly , should we decide to downlink one day, there is a strong debate about displaying or not to controllers the sense of the RA. Seen the mode S delay to display the information, a risk exits that the displayed information will be different of the actual RA ( especially in case of sense reversal ) This could induce again more unwanted and potentially dangerous controller intervention, especially in the time frame when he is still responsible,( i.e. before he gets a pilot R/T confirmation that the aircrfat is following the RA.)

RA Down link will show that the system has issued an RA at one point of time but not that the pilot is following it.
According the latest SOFREAVIA study on the survey of 4 major European airlines , still 10% of the RAs are ignored by pilots , or are acted against .
.

The downlink itself may not show if the pilot is following an RA, but the altitude readout on the ATC screen will be able to confirm it within a few seconds -- or earlier if the downlink is delayed.
As for switching to TA with an engine failure, Eurocontrol ACAS Bulletin 9 (Jul 07) addresses it specifically:
And for those who doubt whether a TCAS RA must be followed when there are contravening ATC instructions, the same Eurocontrol bulletin makes it very clear that following an RA IS MANDATORY despite such ATC instructions:
...as well as in ACAS Bulletin 8 (Jun 06):

Intruder :
Agreed, but it did not work in Ueberlingen . Radar return was 12 seconds there, but on most long range en route radars it is 10 seconds . If the first return is garbled or filtered out by the system ( as it often is the case for sudden aircraft mode C jumps ) , one has to wait until next return to confirm movement and direction.

In any case the main point is that responsibility for anti collision still remains with the controller until he gets confirmation that the aircraft/pilot is manoeuvring in accordance with an RA. So some believe (strongly I might add ) that down linking RAs will make controllers intervention during a TCAS sequence more likely and induce a new kind of problems.

The FRADS/RADE tests conducted by Eurocontrol in Bretigny last years , show controller acceptance of the technical display shown , but did not address the responsibility/ intervention issue.
It will not be an easy one to solve , because waiting 10 or 20 seconds doing nothing when aircraft are on a collision course is not what controllers were and are trained to do.

I am not advocating "doing nothing." However, there are other things an ATC can do RIGHT NOW without ANY change in TCAS logic:

Call a turn.

Ask the Pilot if he is monitoring TCAS. TELL the Pilot to monitor and follow TCAS.

Either of those would have prevented the mishap at Ueberlingen. Why are we so focused on automated intervention in the vertical plane only, when in a controlled environment ATC also has the option of using the horizontal plane? In many cases the pilots are not aware of the other airplane's actual or projected heading/course, so they cannot independently turn. However, ATC has a clearer picture of the collision intercept, and is better able to assess the best turn geometry.

100% agreeing with you Intruder .

In fact if you look at the very first post on this thread ( the one I started ) this was already my conclusion :

Also 100% agreement. This edition of The Controller recommended the same (or very similar) course of action, IIRCC.
Probably the average controller thinks of restoring separation (or preventing a loss) in the vertical plane first, because it is so much quicker to achieve than a turn. As one of my radar instructors used to say, vertical will prevent a loss of separation, faster. But if you chuck in a turn, you might still have a loss of separation, but at least they won't b(@@dy well hit each other!
Quite possibly the environment a lot of us currently work in has got us psyched to prevent a loss of separation at all costs, because of the perceived consequences of same. Be interested to know what a human factors guru would make of that.

Hi all,


maybe I missed it in this thread but don't think so. I'm looking for a link to sensible explanations about how TCAS really works (I understand mode A/mode C basics) but want to know more about how transponders talk to each other. Had an airprox recently and have to write a report, would like to be better informed about how the transponders and TCAS interact.

Thanks.

ACAS / ACAS II are specified in ICAO Annex 10 Chapter 4. I don't know if the algorithms of TCAS 6 or 7 (Implementations of ACAS) were published. If they can be found anywhere, I would be very interested too.

I agree with you, a well advised turn can probably solve many loss-of-separation situations where TCAS and ATC are involved.

Problem is, that TCAS can directly influence the performance of crews, even upto the point that they argue on following ATC advises.

ACAS Bulletin vol6 describes on page 4 a situation, where ATC instructed a 747 to make a turn to the left for avioding conflicting traffic. The 747 pilot identified the traffic on his traffic display and interpreted, that the turn would point him directly into the traffic's path. So he waited longer than normally necessary which led to a loss-of-separation situation.

Again, proper training (in this case, limitations of the resolution of the TCAS display) and oversight would help eliminate this type of problem.

OTOH, as in the personal incident I described earlier, ATC can make bad calls (reversal of turn) as well. So, ANY time there is a TA that looks to the Pilot to be an imminent RA, the Pilot MUST:

Prepare to respond to an RA
Query ATC as to whether they have the traffic and are aware of the conflict. For example: "Center, ABC123, I have a TCAS TA for co-altitude traffic 20 miles ahead. Do you have them?"

Intruder :
If you want to get yourself in trouble, it is a good advice. :hmm:You are going to upset a lot of people down there .

I would also avoid to use the word " must" in here . There are existing ACAS procedures , and so far those MUST be followed. The rest is only our humble opinion, mine included.

I apologise in advance for not having read all relevant posts yet, but i meant to ask in the approach of a humble law student dealing with a moot court case identical to that of the ueberlingen collision only dated 2 years later, is there any ICAO or Eurocontrol document that clearly specifies that one should follow the TCAS-RA over the ATC instructions?