Dozy;
I clarified the FD matter in
post #119 with help from various documents at my disposal. While complicated to explain, the FD operation is fairly straightforward after training and some experience with the system.
It works extremely well, and there is a very good reason why the UAS memorized drill requires that they be turned off.
I suspect you're well aware that building in an "auto-shutoff", like the oft-cited issues with the stall warning NCD matter and the movement of the THS, may create new, separate problems with their own extremely-rare-though-possible risk exposures, and isn't as straightforward a solution as it may seem. It was stated many threads ago that this is a performance accident not a technical one. The issue here is performance, not system characteristics in extremely rare circumstances, for no designer can possibly expect to anticipate and then counter all possibilities and permutations of degradation and system behaviour. As I have observed many times, this is, in essence, sadly, tragically, not a complicated accident.
OK465;
The select VS window on the FCU will NOT be open (i.e. the display will be blank) until the FD's return. There is no active mode until FD's are available.
Precisely.
edit: BTW, in ALT2 the A/P is inhibited permanently for the remainder of the flight.
Which clarifies
BOAC's concern that the AP would engage at "+6000fpm"; It wouldn't, in ALT2B.
The AP would engage in Normal Law but, under normal protections/limits it would also ensure a smooth reduction from an obviously-too-high VS to a stable level-off or gentle climb.
In any case, (because of the Madras accident), as speed reduces, VS reverts from VS to OPEN CLIMB and the thrust reverts to SPEED.