XXTSGR
Not acceptable. Not professional. Not legal. Not safe. Not intelligent.
I'm somewhat disappointed to be characterised as such. I had hoped folks might use the search facility as I suggested as this is just regurgitation of issues that have come up before in numerous threads.
Just for the record, I've been singing the 'follow the RA' hymn for years, ever since being the project pilot for TCAS implementation at our company. At the time, SOP authority to disregard an RA in the event of visual spotting was available, however our training course emphasised in the strongest possible way the dangers in so (not) doing.
If you think an RA is unnecessary, so what. Follow it anyway.
However, if the RA is, in itself, dangerous, then I believe that as professional pilots we have the right to hold final authority.
I haven't yet heard of any sensible reasons for not following TCAS.
Like I said, TCAS is not a perfect system. Here are a few reasons why.
Someone earlier said "Only TCAS sees the whole picture". Well, thats not true. TCAS doesn't see non transponding aircraft, and effectively can't do anything about non altitude reporting aircraft either.
It also doesn't properly see terrain either. OK, RAs have various radalt based inhibitions, but that won't help you if you are flying towards a ridge / cliff / escarpment or over tall buildings / aerials.
Someone else said that GPWS will protect you from ground contact. Thats true, but now check your MEL. Can you dispatch with EGPWS inop? My current aircraft type can. Do you have any AIS related issues or QRH procedures that might require you to disable your EGPWS or its terrain function? My current aircraft type does.
I therefore put it to you that TCAS is quite capable of flying you into terrain or obstructions.
So the point is, that in a potential mid air collision scenario, NO ONE can see the big picture. Not TCAS, not ATC and not the mark 1 eyeball. Therefore any action taken by the crew has to be a composite of the available information, and it is something that ultimately requires judgement, and training.
Now, as it happens, the output of that process should, in 99.9+% of scenarios, be that following the TCAS is the best plan of action.
OK - so neither aircraft manoeuvres oppostie to TCAS advice and what happens?
Now, whilst I can think of scenarios where one aircraft might feel a manouevre in one sense is dangerous, I can not think of any where both aircraft would feel that.
e.g. if at low level over sharply undulating terrain one aircraft might balk at a descent RA, there would be no reason for the other aircraft not to climb.
So, 2 out of 3 of the general kinds of scenarios involve a collision risk with something TCAS doesn't know about - i.e. aircraft and terrrain.
That leaves my 3rd group. Namely that TCAS will command an unachievable rate of climb. Whilst it is correct to say that TCAS has performance based RA inhibitions, it should be pointed out that these are approximate only. With the TCAS equipment we had fitted to the ATRs I was flying at the time, the manufacturers handbook specifically stated that the pilot was responsible for protecting the flight envelope of the aircraft, if necessary to the detriment of following the RA. Simple really, if you are told to climb, but you stall, you descend, (a manouevre in the opposite sense) and therefore more dangerous than doing nothing.
Having looked at the performance inhibitions, they were quite optimistic. Certainly at heavy weights, especially in icing conditions plus actual ice on the airframe, you could definitely recieve an unachievable RA.
But if you are being directed up, then the other guy is being directed down and should have no problem achieving it.
So, in summary, there are reasons why TCAS RAs can be dangerous in themselves. A disregarded RA is NOT the end of the world - the other aircraft will be perfectly capable of solving the encounter and is not going to feel constrained in the same sense.
Therefore the idea that failing to follow and RA means you are "probably going to die" is overly alarmist. Its not supported by data either - there are many documented cases of RAs not being followed where the scenario was resolved by the other aircraft or horizontal separation.
Neither of which means that RAs should be disregarded casually. Defintely not so. Follow the RA unless there is an immediate, obvious, in your face danger.
And in fact, thats pretty much what it says in the links provided by Mike Jenvey below. Here is a quote:
One of the main messages for pilots to note from the ACAS training material is an emphasis on the need for pilots to ‘follow the RA’. Indeed, ICAO Doc.8168, ‘Procedures for Air Navigation Services – Aircraft Operations (PANS-OPS)’, Volume 1, Part VIII, Chapter 3, Paragraph 3.2 c) 1) of Amendment 12, states that: "in the event of an RA [Resolution Advisory], pilots shall respond immediately by following the RA as indicated, unless doing so would jeopardise the safety of the aeroplane".
I therefore put it to you that my contention is precisely in line with ICAO, and is not in fact a 'load of dingos kidneys'.
If you operate good performing twin jets into flat airports with poorly equiped GA aircraft kept outside of the airspace, your chances of meeting a 'dangerous' RA are slim. If on the otherhand you operate a more poorly performing turboprop into regional airports swarming with 'puddle jumpers' and blessed with cliffs / ridges etc the chances start to grow a bit.
Finally, what I can not emphasise enough is that it is manoeuvres opposite to RAs that are the killers.
Rather than saying "Always Follow the RA" it is better to say "If you possibly can, follow the RA. Failing that, get as close as you can. Whatever you do, never manoeuvre opposite."
Mike Jenvey
A couple of points from this incident. Would you not agree that if the second aircraft had done nothing this would have been resolved relatively safely. It is the manoeuvre in the opposite sense that made it so dangerous.
Secondly I find it profoundly depressing that there are still crews making up their own avoidance manouvres based on the Traffic Display. This sort of behaviour should have been trained out of the pilot workforce during the initial implementation of TCAS.
What this tells me is that as an industry we have got the training wrong. We've invested in the kit, but we have paid lipservice to the need to train our crews to understand the system properly. They don't have the right ammount of faith in it. Either no faith at all (as per the incident you report) or too much faith, such that companies view it as sufficient to have proscriptive SOPs.
Lack of training killed the folks at Ueberlingen. Trying to dumb it down is not the answer.
CPB