Hi rudderrudderrat,
Originally Posted by
rudderrudderrat
roll is direct and will constantly need an input until the aircraft is trimmed correctly.
Or unless there is turbulance - true?
It seems to me that the PF
had to make some roll inputs immediately after the AP disconnected, due to the turbulance (page 74, English version), and the (mainly NU) pitch inputs which led to the stall, were inadvertent and unintentional (e.g. perhaps muscular tension (not unexpected due to the "surprise factor"), and/or seat adjustment, and/or l/h vs. r/h seat usage, or other unknowns etc. as has been mentioned here before).
My point is that without having an "H-gate" arrangement (like a manual car gearstick) on a sidestick or control column - which I'm not advocating, of course - then it's impossible to
only make inputs which are only in
either roll
or pitch. There will always be an amount (hopefully very small) of cross-coupling between inputs in those two dimensions (at least in my experience) especially when there is turbulance.
In other words, a design which
requires roll inputs, is going to get
some pitch inputs, like it or not, with a normal pilot - add in the surprise factor, turbulance, lack of high alt hand-flying training etc. etc. and this can all add to the
amplitude of the pitch inputs, which seem to have been unrecognised by the PF, and the lack of recognition then caused the long
duration of that NU input (which, integrated over time, drove the THS movement).
Can we ever expect a total lack of any pitch input, when there must be roll input, during conditions such as those? I'm uneasy (as a non-expert) with adding yet more automation into a situation like this, where the automation can "give up", but I can't believe there isn't a better way than dumping roll
and pitch control onto a surprised pilot at FL350, at night, in some turbulance.
Interesting, the AB design seems to recognise a sort of "keep things as they were" philosophy (not unlike the UAS procedure, when above MSA) regarding the throttle at the point when the AP disconnected, since throttle lock occurs (until deliberate manual control of the throttles is commanded).
If that is appropriate for the throttle (and it seems to me that it is appropriate, for the short term immediately after an event like AP disconnect), why not also for the pitch control (again, until there is a deliberate decision from the pilot to takeover that function, which must
not then be trained for pilots as an immediate reaction)? That would give some time for the PF to "catch up" with what is happening, rather than force him/her to takeover more than roll inputs initially... Just a thought.
[Edited to add: Of course that sort of "pitch lock" idea, would have to mean "with neutral elevators". Perhaps this isn't such a great idea, but I just don't believe that we can expect a total lack of unintentional pitch input, when there must be roll input, and with all the other factors that were against them...]
[Edited again to add: When you said earlier:
Why can't the AP simply hold "ATT" like we used to have with CWS (control wheel steering) 40 years ago?
Is that the same as having an initial "pitch lock" (until deliberately overridden, when the PF has "caught up") which I've been trying to describe (badly)?]