Originally Posted by
infrequentflyer789
We are talking about taking a single protection active in one law/mode and making it available in another mode. In the other mode that protection is part of a set, and the algortihms and code may well be interdependent, so you have to first split out the logic for that one protection and that might not be simple. Setting up the testing etc. won't be as simple either, for the same reason.
I read your "may" as your making a cautious assumption, which is always welcome at the outset. A closer perspective can clarify if the more distant perspective caution is justified.
With the risk of repeating the considerations mentioned by AlphaZuluRomeo, with my own closer perspective and words:
As far as I can remember from when I looked closely at Normal Law protections, in an up-down sequential flow, the elements of the set are parallel, and independent.
Please note, dependency of more than one algorithm on a certain parameter, which, if I recall correctly is the case, does not make the elements of the set of algorithms dependent on each other, or interspersed.
An additional factor is that the Alternate Law is a subset of Normal Law, in fact a minimal subset, which means that the number of parallel algorithms in the set is minimal.
These are both elements that speak about simplicity.
...
However, I think there may be an even bigger problem that is much more fundamental. Looking across the civilian FBW implementations, there is a clear and consistent decision that protections/limits based on airdata are dropped when airdata is not valid/trusted. Either that is an independent engineering decision across teams/types and mfrs (yes, it's the same on B), or it's a regulatory / certification decision.
You need to overturn that decision to put trim protections into Alt2.
It's good to remind us the philosophical and general principles, if there is a suspicion that the "higher" perspective was lost.
But I don't think it was the case, the perspective was/is there.
In the same time let's not loose the close perspective - while we look at the Forest, let's keep looking at the Tree we're concerned about.
The function of the Autotrim is an automation factor to "the Trimmed Stabilizer".
When Autotrim didn't exist, pilots did the trimming Manually - if the "trimmed stabilizer" was present - if there was no "trimmed stabilizer" on a plane, the pilot did NO trimming at all
So, the intention of the "automation" was/is to do the "autotrim", on behalf of the pilot, in those conditions in which the pilot would have done the "manual trimming". This is very important and should be remembered by everyone, pilots, engineers, system architects, managers,etc.... !
What do we have in the AF447 case?
We have the STALL condition being announced loudly - and after so much analysis, very clear in its meaning to us - and throughout the duration of that announcement, we have an "automation" decision/action of employing the "autotrim" to max NU, which obviously if it did anything, it helped the STALL.
So, who do you want to kill ? - because that is what it boils down to. It's normally the engineers faced with the dilema, maybe it should be answered by the pilots ?
The analysis work of last 2 years, performed by appropriate organizations, and the very clear and loud resulting recommendations for the required actions from pilots at High Altitude Stall Approach, or Stall is to bring the ND, which implies the strong recommendation of NO Manual Trimming NU during such conditions!
When remembering the few lines above, that the "automation"s role is to only do what the pilot would do manually if automation was not present, the answer to anyone's dilemma seems simple....extend the "don't do manual trim NU", with "don't do manual/automated trim NU"...
IMO, the recommendations for what "automation" is supposed to do during the conditions of the new recommendations for pilots are just one step behind. The lag seems to be normal, although the current dichotomy
present in some systems will need be resolved regardless of recommendations or not.