@BOAC:
That's really clever - when you inadvertently pitch too much, the system ensures you stay pitched too much. A climb no-one wants or needs - thanks AB
Well, inadvertent pitch up is always going to give you a climb you don't want/need by definition - and it only "ensures you stay" until you tell it to stop.
For every safety measure you can always find a scenario where it will be bad for you. If you are asking "will this ever possibly kill someone" then you are asking the wrong question.
@Lonewolf:
The feature appears to be primarily designed for flight regimes near to the ground.
Agreed, and if I understand it right, it is one of the things that gives AB superior GPWS escape capability. On the other hand, it has acutally
caused one crash on landing (which is near the ground...).
The activation logic has changed as a result.
Clearly if above 30kft, we shouldn't be needing a GPWS escape, so maybe disable it. Then what happens if the plane has dodgy altitude info ? Ah, but what's the probability of needing a GPWS escape
and at the same time the altitude being screwed ?
[ Bit like what's the probability of grid power at a major power station being down for several hours
and there being a tsunami
at the same time... (think about it) ]
No easy answers, and the events are so rare it can be decades before you get a clue if you made the right call.
@galaxy flyer
But, why did the engineers not just make it fly last the last 100 years of aviation. Speed stable (trim for a speed), back-driven so the pilots know what is happening with the stick and rudder, no obscure modes that are confusing in an emergency.
You know, I admire the boeing backdrive, impressive feat of engineering - but there's still a nagging doubt that it's added a whole lot of complexity, and hence failure risk. All to give the pilots a "feel" of something that hasn't acutally been there (ie. direct cable control) for decades. That "feel" is something you want most when things go wrong, but, you know, it's precisely
when things are going wrong that
you shouldn't trust it - because it is purely artificial and is
calculated using the same airdata, config etc. information that may be what is going wrong in the first place.
The backdrive has limits (soft, not hard, but there) - if the a/c is flying on bad data, those limits will be in the wrong place. I am also pretty sure it will use airspeed etc. in calculating gains even within the limits - lose airspeed and are you
sure the feel is going to be "right" ? If it's dark over water and your instruments start acting up, and the autos drop out, are you going to start flying the plane based on that backdrive feel - even though it's being
calculated from the same airdata that you
know is screwy ? Is that better or worse than "no feel" ?
And, of course, the backdrive is modal too - or at least sometimes it can cause "higher than normal control forces" in a way that is, as you say, "confusing in an emergency". But that's ok, no one's died so far, and there's an AD for it now - a software fix to make sure we don't activate that mode at the wrong time. That sounds so very... airbus, doesn't it ? [ But I'm sure you B fans will
know the AD and I don't have to dig out the reference, right ?
]
It's an imperfect world, A or B side, fbw or non. Both fbw are very safe, but also very different. Feel free to have a preference as to which is nicer to fly, but as to which is safer to fly
in - I don't believe there is anywhere near enough data, and too many variables, to separate them.