Originally Posted by
Uplinker
Well, actually PM's side-stick could be designed to be ignored by the FBW unless and UNTIL the take-over button was pressed. On pressing the take-over, PM's 'stick would become active and PF's; inactive. That would exactly prevent dual inputs happening, but still allow PM to take control.
But Airbus did not engineer it that way - why ? Nor did they provide a take-over button for the tillers, and the "dual input" warning does not activate when dual tiller inputs are made. Why is that ?
Think about risk assessment. If You want to exclude a primary flight control You must willfully do it, this applies to all the airplanes where there is a possibility to exclude the other Crew Members primary flight controls. Simply acting on a flight control cannot exclude the other.
Originally Posted by
Uplinker
Yes but remember in your very initial PPL training, when the instructor occasionally applied pressure or even firm corrections to their yoke when you were learning and feeling how to flare for the very first times - without the "I have control" full dramatic take-over, just gentle guidance and finesse.
Completely taking over is not gently correcting, and the cadet is left feeling that they screwed-up big time rather than simply being guided.
I was often invited to "follow me through on the yoke" when learning to land my first commercial types, and deal with crosswinds etc. You cannot do this with un-linked controls, and I think Airbus engineered the arithmetical addition and keeping both 'sticks active to allow this sort of assistance, and the ability to quickly "nudge it" to avoid a prang.
Cadets are now going from a flight school Diamond 42 straight onto an A320 large jet, rather than gradually building up skills and experience via small turbo-props, larger turbo-props, small jets and then large jets. So the first flares and landings on the A320 family are going to be a huge step from what they are used to. The first few might therefore be a bit sketchy, and I suspect that Airbus designers allowed both 'sticks to be always active to allow a TRE to prevent it going bad, or gently nudge it, but without all the drama and stress of "I have control", and taking over, which would destroy confidence.
Why not though ? You have that facility on every other aircraft type, why should it be denied on Airbus FBW ? The Airbus side-sticks are not mechanically linked of course, so this arithmetic addition is probably the closest way of simulating it.
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It is all tied to a different design philosophy, whereas we can achieve the same results but through a different process.
Your inputs also serve as an opening for a very important aspect: it is of utmost importance that instructors properly teach the landing technique to the trainees at SIM stage -which is often not the case- and then the issues are transferred to the line. We have, more or less, all been there.
As discussed before, the trainee must be aware that during LIFUS the takeover is absolutely normal, especially at early stage. What becomes important afterwards, during the debriefing, is that the instructor identifies the root cause of the takeover, otherwise the one who fails at the job is the instructor, not the trainee. Within the next few landings the root cause will be tackled and the problem solved. Providing the trainee with "a little help" during flare is a short-term fix (again a no-no on Airbus FBW) that does not address the root cause.
During instructor training, the instructor trainers have to highlight the most common "mistakes" made by trainees of different level of experience -cadet, experienced changing type, etc..- and raise awareness to find solutions. We are looking at permanent fixes as quickly as possibile, that is the idea.