PBL,
Please read my analysis of the decision problem presented to the Bakshirian crew at Überlingen. They were faced with an "intruder" at 10 o'clock which they saw, and an unknown conflict at 2 o'clock which they didn't see, and for which they had an advisory to descend (that is, he was at or above their altitude).
The (sadly last) communication from the Tu-154 to Zurich was: "'Ja', we have traffic at your... 2 o’clock now at 360". Where does the idea of an "unknown conflict" come from?
What would you do? Climb towards another conflicting aircraft that you don't see but ATC does? Or avoid him, descend towards an aircraft that you do see, and hope to avoid him using visual means?
What does the TCAS have to say about it? Follow the commands to resolve the conflict. Done. To reverse the question, why would I
not follow the RA? You have 18 seconds to reply...
May I respectfully suggest that you're trying to find a complicated answer to a simple problem? The sky is often full of aircraft, some you can see, some you can't (try an approach to EWR or JFK on a busy day). The sort of scenario you're talking about is not uncommon; in fact, I would go as far as to say, unremarkable. Installation & use of TCAS is compulsory in the USA and Europe in most airspace that airliners use; if we all went about 'doing our own thing' in reponse to RAs, I don't really want to imagine the consequences. Until someone
proves it otherwise, I shall be 'staying out of the red', thank you!
bsieker,
I think you misunderstood. One cannot tell that these probablilities are "low enough" to disregard them. Since we do not know them, perhaps never will, they may be quite high.
Given the amount of flying hours logged and the number of incidents (and I'm talking generically about systems) one should be able to set an upper bound on the these probabilities, given certain confidence limits, just like you would with any other experimental data?
And yet, the Ueberlingen accident would not have happened, if neither aircraft had been equipped with TCAS.
Not possible I'm afraid. We all have to have it. Therefore we need a common standard in how we respond to it (which is where I came in on this discussion).
All,
I'm continuing to partake in this discussion because I don't want any impressionable pilots reading this thread and thinking that it's a good idea to start tinkering with standard responses to RAs (especially if I am in the other aircraft). I'm all for academic arguments and theories as that is the way we progress science but in many cases there has to be a set way of doing something until we build up enough evidence to justify changing it. This applies especially to aviation.