Originally Posted by
ChrisVJ
I declare my amateur status, just another seeker after information.
I would think, in view of the importance of Pitot tubes, that they should be at least of different types so that a common failure did not cause them all to fail at the same time.
Dissimilar components cause as many problems though. If you want to rely on being able to compare the outputs, then the components have to be practically identical. In particular, you're forced to design to at least the same specification, and perhaps the actual same design details (in the case of a pitot probe, geometry for example). So the same extreme conditions which will disable probe A will quite likely also disable probes B and c anyway. meanwhile you have to deal with the nuisance of 2 or 3 suppliers for one part, carrying more spare parts in the maintenance pool, and so on.
This may well not be common failure - in the sense of the probes being at fault - it may be the case that the environment was too much for them.
Suppose you wish to drive your car quickly, and put high speed-rated tyres on all 4 wheels, but to "be safe" you go for one Michelin, one Goodyear, one Bridgestone and one (someone else). Then you drive at 20mph over the rated limit for all the tyres anyway. The fact that they are dissimilar sourced won't do much good, in all likelihood. You're pushing them all outside their design spec anyway.
I understand three pitot tubes and three ADIRUs. Do A330s also have a steam ASI? If not I can imagine that all three pitot failure would be very difficult at high altitude, turbulence, even moderate, and in the dark.
ISIS is the "integrated standby" for when the main three systems fail - but it still has to source pressure from outside, so again, the environment could well be the issue. Not the aircraft components.
Is/are AoA indicators part of the pitot tubes?
No, different component. Some a/c use measured AoA to correct the measured air data - I
don't know if this is the case for A330 or not.
Are the Pitots electronic, ie, are there sensors in the pitot heads or are there still air pressure tubes back to the ADIRUs. Are the static heads duplicated for each pitot head, do alternate static cut in automatically, by electric switch or (like mine) by pulling a plug/ turning an air cock? (Or am I being naive assuming there is alternate static?)
Air pressure lines to the ADIRUs,
I believe. Most large a/c will have duplicate (left/right) statics for each pitot, to balance sideslip effects; again,
I expect that to be the case here. The back-ups are through the multiple ADIRUs and ISIS -
I doubt the crew can reconfigure the system beyond selecting which ADIRU they can display data from.
I'll remove my speculative statements if/when someone more knowledgable comes along