Hi
Originally Posted by
airtren
The suggestion in essence was not intended as to provide more automation, or a different automation during a Stall, but rather reduce or eliminate the automation of the THS, in association with placing the THS in the "most optimal" position for the Stall Recovery. What the latter means, in terms of "optimal position" can certainly be the subject of more studying, but as a start can be considered THS Neutral.
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 ? This way :
- you prevent the automation to make the situation harder/longer to solve (THS full up = reduced ND effectivness = bad when stalled)
- but you don't inhibit/freeze totally the auto-trim (if you apply enough ND stick, the THS will eventually move ND too)
- 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.
Am I missing something?
I'm not sure that it will have changed anything substential in AF447's case, but I thought it was worth thinking about it.
On a side note, re the clues the crew had about the THS position : There was the
trim wheel index, but also the
F/CTL page on the center screen (showing all the control surfaces state, including numerical value for the THS angle). That page was automatically called due to some of the failures AF447 encountered (see ACARS analysis in interim reports #1 & #2).
It was not enough for the crew to notice. Sensory overload I guess?
I then support the idea of a clicking trim wheel, as it may give "another chance" to notice.