AF447 is an example of a fly by wire system that has to keep working no matter what happens, thus a bunch of redundant systems and a series of alternate modes the system can fall back on to operate in a degraded state.
MCAS, in contrast, is not a critical system. It could shut down with no problems at all. These crashes happened only because it didn’t shut down when faced with a failed sensor, because it couldn’t detect the failure.
AoA sensors by design don't work reliable in low speed and they don't work at all on the ground.
> AF447 is an example of a fly by wire system that has to keep working no matter what happens, thus a bunch of redundant systems and a series of alternate modes the system can fall back on to operate in a degraded state.
AF447 is a good example that two AoA sensors can simultaneously have same erroneous readings. It's not that unlikely.
Airspeed is a critical system while aoa is not. (Unless aoa is tied to mcas like in the max jets)
You’re just badly arguing details while ignoring the actual point here.
What was the point? Two sensors (in this case alpha vanes) can fail at the same time and in the same way on an Airbus:
> First: I said it’s very unlikely, not impossible.
> You’re just badly arguing details while ignoring the actual point here.
My point here was that with two AoA sensors you can't reliably detect failure. They can both fail simultaneously and provide the same erroneous readings. And because it's not that unlikely we have to be sure that pilots can handle MCAS problems when two AoA sensors fail.
> Second: the failure of AF447’s pitot tubes was detected immediately
Because A330 have three pitot tubes, right? Not two out of two sensors?
I'm not arguing about AF447 case, I gave it as an example that two sensors _can_ have same erroneous readings. Airbus engineers were not sure that can happen in real life, so stall warning issue was a real surprise for them.
They don't have to fail simultaneously in a flight. And they don't have to fail by internal sensor problems. There are many cases in which they can simultaneously fail and give same readings, article even mentioned such types of events:
>> That probability may have underestimated the risk of so-called external events that have damaged sensors in the past, such as collisions with birds, bumps from ramp stairs or mechanics’ stepping on them.
And AF447 gives an example when such erroneous readings combined with pilot errors may lead to.