Comment by olliej
6 years ago
I don't mean validation == determine which one is correct, I mean "make sure they agree" and don't trust them otherwise, which, as far as I can tell, is how other Boeing systems work?
I mean there's also the space shuttle system where you have N redundant systems controlling N separate motors (or whatever), and assume that if you'll never have >= N/2 producing incorrect output. That's a "no validation" approach that works by virtue of the correct instruments literally overpowering the incorrect ones.
Supposedly an Airbus plane had triple redundant sensors and two of them failed with the same reading and the good sensor was voted off the island.
I'm walking away with the following explanation. Boeing made a breaking change to the aircraft and did such a good job hiding it from themselves, the PAA, and pilots that they made it impossible for experienced pilots to handle things when it failed.
[edit to clarify: I'm not disagreeing with Gibbon1, I'm literally just curious about these questions and would love to know the answers]
oof, what makes AoA sensors so terrible? Also, it seems like if you have something that isn't particularly robust (pitot tubes apparently also being egregiously terrible in that regard), surely having a less accurate but more robust reference tool would be a good "oh bollocks" back up. e.g. additional redundancy based on different technology.
AoA sensors and pitot tubes are simple, purely mechanical devices that have to function in wind ranging from at least 0–700mph+ and in temperatures ranging from at least -60–120°F. They have to do this for tens of thousands of hours without failing. They have to survive being iced over repeatedly, being impacted by hail and rain, and all sorts of other difficult conditions that make reliability really challenging.
It’s a difficult problem to solve! These sensors are already probably much closer to what you would expect a low-fidelity reliable backup to be than you realize.
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