Originally Posted by
CONF iture
Airbus, with reason, put in place some restriction to not autotrim all the way when everything works fine, but decided autotrimming all the way was the way to go when data acquisition was known as deficient …
Incorrect. Autotrim is never inhibited or restricted directly (on the A330 at least), it is subject to the protection limits in the same way that autoflight or human pilot input is in Normal Law. Take away those protection limits (i.e. in any law below Normal) and any of the aircraft's controls (including trim) has full authority.
I don't see what's graceful in such degradation ?
I question Airbus on such 'logic' ?
That's because it's what you want to see. You're so invested in the idea of Airbus's logic being wrong and that their intent was to restrict pilots that you can't see the wood for the trees - in this case the design is intended to give full authority to the pilot in every axis precisely because "data acquisition was known as deficient".
If the pilot mishandles the aircraft outside Normal Law then the chances are good that something's going to go amiss, but that's true of every aircraft flying, not just Airbus.
I repeat -
autotrim only worked against this crew because their control inputs were inappropriate, and if they'd realised their situation and applied corrective inputs then autotrim would have helped them get stable - until quite late in the sequence.
Now - I can see either putting an extra alert or (in extremis) limiting the autotrim angle being a possible option, but as studi pointed out:
Originally Posted by
studi
There is a term for this in flight safety: black swan event. They are so random and so unpredictable, that if you start to adapt technology to the specific event, a totally different unexpected thing will happen and fail your adapted technology.
this comes with a risk - especially when such a change is in response to a single incident that was way outside the bounds of acceptable aircraft handling.
But more than anything, I do question the BEA on their apparent lack of curiosity ?
And again - just because it does not mention a specific item in the report in the way you want it to (because trim response to SS input is covered in the sequence in some detail) does not mean that the investigators didn't look into it.
Originally Posted by
RR_NDB
Question:
Graceful degradation is the same in both?
They can't be, because the control philosophy is different. Airbus used advances (in 1982 terms) in technology to rework the concept of an airliner cockpit from the ground up. Boeing used the fact that their technological starting point was later (about 1988-89) to create a more complex system that restores a more traditional feel through artificial means.
FM (frquency modulation) has the so called "threshold effect". Up to a certain level, everything is fine (excellent Signal to noise ratio).
Below a certain level worms, dominate the scene. So aviation uses AM.
I'm a little lost by this - if we're talking code complexity here, the Airbus logic is actually incredibly simple (in software terms), even by the standards of the time.