Originally Posted by PJ2
By "stable, level flight" is meant maintaining an altitude while accepting small excursions above and below the exact altitude to maintain and not climbing or descending. It's never going to be "level" in the exact sense.
Is this what you meant? Tx...
Indeed, the "a/c" trajectory is never really a "perfect" "straight line". It is rather a series of segments of the type I've mentioned - "up", "down", "left", "right", "level" - with the length of these segments depending on the degree of air turbulence, and how fine the control of the "a/c" is.
In non turbulent air, the 4 "non-level" segments are very short, while the "level" segments are long, or very long, and predominant.
That is different in turbulent air: the length of the 4 "non-level" type segments is a lot more significant, while the length of the "level" segments a lot shorter, possibly down to "zero", with a predominance of the "non-level" segments, versus "level" segments.
That implies more drastic or significant actions of the "a/c controls", that react to the change and transition from one type of segment, to the next, to keep the "a/c level".
Originally Posted by PJ2
But as you say, it is going to remain more or less level out of it's own inertia and the position of the control surfaces, etc.
My understanding is that that would be the case if there is no, or little turbulence.
However in turbulent air, at an "a/p and a/thr disconnect", which can be coincidental with a change of law, and loss of certain protections, the "inertia" and the "a/c control surfaces at normal position" would keep the "a/c" level, ONLY and ONLY if the segment is "level".
Otherwise, as I understand it, if the segment is "non-level", there is a good chance/probability that "inertia" and "control surfaces" as left after the disconnect, and lack of protections, can bring the "a/c" way out of being "level" - "up", or "down", or "left" or "right". The degree of how off from "level" depends also on the time interval between the "automation disconnect" and the taking of the controls by the pilot, as well as a correct control correction coming from the pilot.
The probability of 20% and 80% I've referred to implies an equal distribution and length of the 5 types of segments, which is a stretch, for the sake of an easier explaining/understanding .
But it is a stretch in both directions!!!
Which means that for a very active turbulence, for the duration of that turbulence, the segments might be only "non-level", in which case in that time interval the "probability" goes from 80% to 100% - which makes it "a sure thing".