Originally Posted by
RR_NDB
The worst case scenario is just one failing?
Well, the worst-case scenario where the automatics can continue to function is, yes, because a software-driven triple-redundant quorum can only be effective if two components are working correctly (in this case giving readings within the acceptable tolerance range)
I've moved your quoted post around a bit so that my reply can deal with the questions properly - hope you don't mind.
Question (yet posted earlier): Why they put this redundancy? For what reason? What benefit?
Simple - as has always been the case, computers are better than humans when it comes to monotonous, repetitive tasks like comparing readings in a data stream. A computer will be much quicker at flagging a pitot failure problem specifically than a human will be able to. Compare the previous generation's B757 - classic triple redundancy with the flight computers linked to a single air data input at any one time - where, originally, the first warning you got was "MACH TRIM - RUDDER RATIO". This is logical in terms of the systems engineering, but to a pilot the message could be confusing. They later added an "AIRSPEED DISAGREE" warning if I recall correctly.
Redundancy is "powerful" when critical elements do not fail simultaneously. And UAS cases show clearly simultaneous "failing" (due product limitation)
Simultaneous "failure" of critical elements should be reported immediately.
They were, and there was a service bulletin in effect to replace the components (along with pilot information to assist recovery from the issue) - unfortunately the airframe that became AF447 had not been taken into MX for that fix yet.
@Chris Scott re: misquoting, no problem. The problem I have is how the system would attempt to calculate G-loading in this scenario. The whole design ethos seems to have been based around making sure that the computers did not interfere if any data was missing, because at that point the pilot is best suited to keeping the shiny side up. Of course, even if this was the case, you've got 3 ADIs in front of the crew telling them they're too nose high, so why is the stick neutral or back? IMO this is the 300-pound gorilla in the room that the people who want to blame the aircraft are wilfully ignoring.