AlphaZuluRomeo, thanks for your reply, and ideas.
Originally Posted by
AlphaZuluRomeo
Hi
I agree with the first of your ideas (reduce or eliminate the automation of the THS) but not with the second part (repositionning the THS to neutral when stall warning is ON), as I feel unconfortable with this last idea.
Why not "simply" prevent any further NU movement of the THS by the auto-trim while the stall warning is ON ?
The reasoning for returning the THS to a Stall Recovery Optimal Position - I picked Neutral as that seems the best candidate - is that from other BEA reports it seems that in other Stall incidents, unlike AF 447, where the THS was started the move NU after the Stall, the THS was further NU, or max NU already before the Stall.
A THS Stall Recovery Optimal Position is one, which yields the most effective Elevators ND, and NU actions, which are needed in a (quite) quick sequence during Stall Recovery .
- but you don't inhibit/freeze totally the auto-trim (if you apply enough ND stick, the THS will eventually move ND too)
As long as the Stall is ON, as it is a slow move/reacting surface, I would not risk interference with the Elevators, which need be quickly very effective, and for short time intervals.
- you don't prevent the crew to manually apply (trim wheel) more NU or ND trim depending on their assessment of the situation
- you don't add another alarm (USE MAN PITCH TRIM type) to an already stressed crew to process.
Manual control of course remains. Sound alarm can become easily a disturbance, so agree. A visual - a LED - would, IMO, be useful.
I'm not sure that it will have changed anything substential in AF447's case, but I thought it was worth thinking about it.
The Elevator NU would have been less effective, while the Elevator ND would have been more effective. Which means different pitch angles and AoAs - less NU, more ND. That we know. This could be simulated. Would they have taken advantage of it?