I differ with PBL on the likely causes of the Bashkirian crew’s decision to descend. My reading of the translation of the CVR is that they were in a simple dilemma about whether or not to obey the controller or TCAS. I don’t see any evidence for worries about two other aircraft in the Russian cockpit in the report or the CVR.
They chose to follow the controller instead of TCAS because their training on and experience of TCAS was very limited, and also because their manuals stated that a TCAS RA was a “recommendation” to the crew, not an absolute requirement. On the CVR the Russians don’t mention two other aircraft and when they see the DHL they only ever talk about “it”.
I don’t see how PBL can argue that the 10 o’clock versus 2 o’clock confusion was “crucial”. He says nothing to contradict the more obvious interpretation, which is that they were conflicted about what to do and made a bad choice.
PBL’s point 1 is strange. Is this really the TCAS “philosophy”? If that is printed somewhere, I would like to see it, as it seems a strange and illogical assertion for software experts to make. They are only dealing with their own system. ATC is another system. Where the designers, regulators and ICAO failed was in not emphasising strongly enough the dangers that would arise when both systems issued different orders to the aircraft at the same time.
As ATC Watcher pointed out before, when you translate the American “advisory” into other languages it often does not come out, as it should, as “command”. Secondly, there was little acount in TCAS’ implementation of the vital importance of stressing that you must never ever do the opposite of a TCAS RA. The strictures against this were well buried in the TCAS manual. Now, every pilot has burned into the brain, “Never manoeuvre contrary to an RA”, but before Ueberlingen, less careful airlines with less careful regulators and sketchy training regimes could fail to see the crucial importance of this rule.
I don’t mean to criticise PBL on the software and algorithms front. I haven’t the first notion about them, but I do think that the “three-aircraft scenario”, while of importance to flight safety was never a feature of Ueberlingen.
Finally, to say, as PBL does,
“I cannot think it wise to advise people to *always, without exception* follow an RA..”
is the height of irresponsibility. Perhaps not “follow”, but the golden rule of “Never manoeuvre contrary to an RA” is just that, golden, and to argue otherwise is very dangerous indeed. All sorts of incidents have been recorded where pilots thought their visual intepretation of a TCAS situation was better than the gizmo’s, and they were wrong every time. PBL’s comment is just the kind of thing that could possibly introduce doubt in the minds of pilots.