Hello gums;
Re, "
So question is: does HAL keep commanding the last A/P inputs or not?"
No, it doesn't. As you'd expect, AP orders stop the moment it disconnects.
However, flight control orders (C*), maintain the last pitch and bank attitudes until manual control input order a change. Roll is a roll-rate request until Alt2 Law and pitch remains a gee request until Direct Law. I know you know all this...just reviewing!
That means the controls on the wing and stabilizer are "busy" maintaining the last ordered attitudes...they're making tiny movements, but only for this reason. The AP has no input and neither does the stick so long as it is in the neutral position.
Should manual input be made, the controls will move according to such orders, while "on-the-fly" maintaining last ordered position. Once the orders stop, the airplane stays in that attitude.
I can't say whether a slight NU input is made to counter the slightly-increased gee at higher bank angles, (say, 20deg), but I know in Normal Law beyond about 33 degrees one has to pull a bit to maintain altitude in the turn.
So flying in turbulence, even moderate, is straightforward and is done with tiny stick movements because the airplane is already attempting to maintain last attitudes, in Normal Law and is doing so with exactly enough aileron and elevator. Maintaining bank isn't the case in Alt2 as we know and Roll Direct is sensitive but no big deal in terms of control. The airplane isn't about to roll over to 45deg+!...not unless the pilot does it and Bonin got the roll under control very quickly. It's a very stable airplane. It flies very well at cruise altitude under manual control.
By way of emphasizing this point, I've flown the airplane manually in turbulence a number of times (A320 as well), and really, it's not a big deal. One makes tiny inputs, just like the AP! Everybody out there on the wing is already doing their job trying to keep the last ordered attitude!
In Roll Direct (Alt2) that isn't happening but that doesn't mean the airplane is about to roll over! Tiny SS inputs again, and like I said Bonin got the hang of it really fast and had stopped the roll oscillations.
The question of Why the sustained pitch up?, may never be answered. For the record, in
July 2009 in a response to
stepwilk I stated that the correct response was to "do nothing" and initially got some flack for saying so mainly because the phrase "do nothing" was misunderstood as really "doing nothing", when of course maintaining pitch and thrust was what I had meant! Anyway...