Originally Posted by Frangible
....... with no TCAS, there would have been no collision. Equally, however, if there had been no ATC, and TCAS only, there would have been no collision.
Both correct. (I omitted the word "axiomatic" since I am unsure what you mean by it.)
Originally Posted by Frangible
This is my point about demarcation – mix up the boundaries and you court disaster.
Now that is an interesting, and likely mistaken, viewpoint.
Boundaries between systems *are* mixed. It is necessary, indeed essential, to study the interactions. And as far as I can tell, that has not been done analytically with TCAS and ATC.
The Eurocontrol ACASA project did a bunch of simulations and analysed them thoroughly, but they did that with about two days' worth of actual data. Unfortunately people have drawn conclusions from that data about system interactions which claim to reach accuracies of one event in O(10**9) operational hours, which mathematically speaking one cannot justify from that limited data. Great project, but there seems to be a human tendency to claim what senior management wants you to claim, rather than to claim what your data support. That is why I like hazard analysis.
Similar happened with the Space Shuttle. Feynman's appendix on risk and hazard analysis to the Challenger report, cited on the Okinawa thread, makes a good read on that topic.
Originally Posted by Frangible
it was by no means clear to me that you were using Ueberlingen as template onto which to put speculative scenarios. Now I see that, this debate becomes less interesting to me. ...... I don’t see how “decision-theoretics” are helping.
Shame. But each to his own. I just wish that more professionals understood how hazard analysis works.
Originally Posted by Frangible
...... you should not go around saying it is unwise to advise pilots always to follow the RA.
It seems to me you are not quite reading what I said. See my reply to Spitoon.
PBL