AlphaZuluRomeo, thanks for the follow up.
The Stall Warning reliability is among the concerns raised with the AF 447, here on this Forum, as well as the BEA report. I am confident, or perhaps just hoping that it is going to result in a BEA recommendation, and will be mandatory to address.
I understand your perspective, and I perceive it, as being in the same direction.
Perhaps with the risk of repeating myself, I see in general the time constraints of the Stall Recovery as a very important parameter. There is very little time for such a Stall Recovery - we know it took about 3 minutes to loose 38K ft of altitude - and with the THS being a slower moving control surface, I see it beneficial to have the THS down to Neutral sooner, rather than latter, and let the Stall Recovery be handled with the Elevators as a main element.
Originally Posted by
AlphaZuluRomeo
Hi airtren
I understand your point, it is valid but I still feel uncomfortable with it, because:
- it adds another layer of complexity to be aware of (KISS)
- it may be dangerous if stall warning isn't 100% reliable (and it's not)
- the crew must react to the stall by pushing ND. That would give ND elevators, then ND THS if the latter was NU by far.
(note : on AF447, if one accepts that the flight control surfaces acted accordingly with the crew inputs, the crew never pushed enough on their sidestick to make the elevators go ND, only less NU)
I am sorry for not being clear, or not using a better word. Let me try to clarify - sorry if there is any repetition.
The use of "interference with the Elevators" was meant as "diminishing the effectiveness of the Elevators".
Specifically, it was in reference to the effect of a THS NU, versus a THS Neutral when summed with the Elevators ND, for the first phase of the Stall Recovery (ND command, gain speed, loose altitude),
efficiency THS NU + ElevatorsND < efficiency THS Neutral + Elevators ND
respectively the effect of THS ND, versus a THS Neutral when summed with the Elevators NU, for the second phase of the Stall Recovery (NU command, level off, stabilize and start regaining altitude).
efficiency THS ND + ElevatorsNU < efficiency THS Neutral + Elevators NU
In both cases, the THS Neutral is more "neutral"
than the others.
An important consideration was that while it is true that the non-neutral effect of the THS may mean "amplifying", as opposed to "diminishing" - for instance THS ND with Elevators ND, and THS NU with Elevators NU - for the duration of one of the two phase of the Stall Recvery, it is also true that the Slow speed of the THS move, is a factor that may transform the "amplifying" during phase 1, into a "diminishing" in phase 2, at the transition from phase 1 or phase 2 of the Stall Recovery.
The short time available for the Stall Recovery, requires a very quick. and very effective ND to NU transition from phase 1 to phase 2 (described above), with fully effective Elevators - any "diminishing" is undesired.
I hope it is clearer.
I don't think I understand which interference you may be refering to? I didn't suggest to limit the elevators in any way, only to prevent THS NU move.
I agree that if THS stays where it is, the recovery may be a bit longer than with the THS neutral (or ND), but as the crew has to push SS ND, elevators will go ND and eventually THS too.