Originally Posted by
CogSim
That maybe the case. However, there is more to performance than "quality". There is a fundamental difference between how "software" performs and how the other systems you mention behave. I believe it was RR_NDB who brought up Taleb's "Black Swan". So I'll invoke that concept. Hydraulic pressure cannot go to infinity. Similarly the pressure cannot go zero 0 in zero time. See RR_NDB's comments below about analog systems. Yet, it is too easy for this sort of nonlinearity to crop up in software systems, especially at the points where the software system fails/degrades (a.k.a bugs).
It appears to me that RR_NDB, like many others, is working backwards from a hypothesis that something intrinsic in the way the Airbus control system is designed is, in whole or in part, responsible for the accident.
My position is that I don't know any better than he does, and the fact is that none of us will until the investigation has run it's course. However, as someone who is pretty well-versed in software disciplines, I'm simply trying to put forward what I know about what my peers have done to try to aid pilots in the day-to-day running of their aircraft. Not to de-skill their jobs, and definitely not setting in motion a trend towards pilotless airliners, but simply to assist.
I of all people am well aware of the ways in which digital systems can behave bizarrely when the inputs are outside of their design limits - in fact I deal with it almost every day, which is why I've been at pains to point out that the design of the systems took as near as damn-it every possible input into account before the systems were even let near an airframe.
The story of the DC-10 proves that even with the best intentions, unexpected failure modes can cripple mechanical and hydraulic systems in unforeseen ways, which is why I get so frustrated when people assert that such things did not happen before the advent of computer control in transport-category aircraft.
Perhaps conditioned by the blue screen of death. I kid. I understand this was the point you were trying to make that mission critical software systems are not like your average windows pc. In my book this only means, its damn hard to "beat" these "ultrareliable" systems. However, when they do fail (for whatever reason) they exhibit the same kind of nonlinearity that any old windows computer would.
And when they do fail they are designed to fail gracefully. In the case of a severe failure they will do exactly as many demand, which is to hand control back to the pilots in the form of Direct Law.
If you can find me a single fatal incident that was entirely caused by the software systems on a FBW airliner - Airbus or otherwise - then I'll cheerfully take my ball and go home. Otherwise, I'm happy to go round the houses for as long as is necessary - refuting some of the falsehoods routinely propagated about computer-controlled aircraft.