THS position-indication and "Vc Prot Law"
PJ2,
Thanks for reminding me that the THS display on the ECAM F/CTL page (the lower display unit, not normally displayed in the cruise), would have eventually shown either
"13° UP" or "-13° UP" for what I refer to below as "13NU". (Perhaps you can tell us which?)
As far as I know, the crew were not presented with any ECAM drills on that lower DU, despite the various failures timed at 0210 and 0211. Presumably, the CRUISE page would still have been displayed, which does not include THS? If so, the best way of reading the THS position would have been the scale on the manual pitch-trim hand-wheel, but that involves turning the head. As I think you said, there is no "whooler", or equivalent, to announce THS movement.
Quote:
The THS response to sidestick orders is immediate, in other words. I believe then, that as the sidestick was held in the NU command position, (orders still gee-referenced but with rate/gain limits), the THS would follow through, likely at a varying rate in relation to slightly changing sidestick orders. I think once the AoA was below that which the autotrim ceases to function, it would respond to sidestick ND orders.
[my highlighting]
I'm not sure you needed to include the clause highlighted, so will try to explain why.
From 02:10:51
Would the auto-trim look at AoA when and while the system considered the AoA data invalid? Was the "Vc Prot Law" or "limited-authority stability order" of Andy Tracey's paper disabled some of the time – or constantly? When the stall warning was operating, the AoA was considered valid, so the THS would stop provided the stick was neutral.
When the stall warning was not operating, the THS could auto-trim if the AoA was below the stall-warning threshold. And if the AoA data was invalidated, my understanding is that it could auto-trim regardless of how high the AoA was.
But would the back-stick not have overridden the "Vc Prot Law" anyway? If that was not the case, would the THS have ended up at 13NU?
Hope this makes some sense.