Originally Posted by
Uplinker
I have always wondered about this. Why do Airbus side-sticks arithmetically add if they are never supposed to be operated together ? I think the intention is so that a TRE can grab the situation and pick up a wing in the event of a bad gust near the ground, or a missed flare, or a bounce, that a trainee does not react appropriately to, to avert a prang. If they also press the red button, fine, but even if they don't, they can still save the situation. I suspect that the "Dual Input" warning was provided for the trainee to be aware that their instructor was correcting on the non linked side-sticks.
Some years ago I was taxiing out at JFK and my Captain suddenly slammed on the brakes because I had slightly strayed off the centreline in a turn. The whole 230 tonne aircraft dipped and shuddered and lurched to a stop which was far too dramatic. If he had simply used his tiller to steer back onto the line and said something appropriate, it would have been far smoother and less alarming for all concerned, including the passengers.
.....Indeed as I myself did to another Captain when he went wrong - I just steered him back to the centreline with my tiller and asked if he was OK. No dramatic emergency stop required, just a gentle tweak.
Obviously, you absolutely do NOT want both pilots applying simultaneous inputs to their side-sticks routinely during normal flying or taxiing, but the facility is surely there for very occasional emergency corrections.
Originally Posted by
sonicbum
The only reason the inputs are algebraically added is because there is no better solution; it is the one that makes more sense from a design point of view.
The “Dual input” is a big no-no. It’s a warning rather than a caution like: “you are not supposed to be doing this”.
In your example of a bad gust near the ground you push the TakeOver PB and you correct. the sentence “I have control” is simultaneous to pressing the red button.
Trainees of any experience level have to be taught by the instructor from Day 1 that on Airbus FBW there is no room for “a little help in flare”. So if needed the instructor/cpt/FO (incapacitation) will takeover and no hard feelings. It’s absolutely normal.
Originally Posted by
BUSSPilot
The Airbus recommended techniques for taking over during take off and landing is by pressing the take over push button and keeping it pressed - irrespective of how many tenth’s of a second away we are from the main wheels touching the runway. From my personal experience I have found that it has worked well enough. I suppose it’s prudent to ensure you are not too late to exercise the use of it. Airbus golden rule - Take action if things do not go as expected. I am sure using the Prompt-Assist-Takeover model or its equivalent at your airline should help mitigate these issues.
As far as discussing the disadvantages of your proposed “software update” - why should it be deactivated for a training flight and not regular line flights? Are these tail strikes happening only during training flights with first officers on the CM2 seat?
It should be applicable for all flights. And the software update obviously isn't for CM1. The priority can be assigned in advance. Tailstrikes are more likely after a bounce followed by a landing or go around when both pilots give control inputs. Also, the Capt can correct for only what he sees at that moment and not cater for what his/her FO is about to do. FO still has the TO pb as an option to cancel the priority logic.
Question is, what is the disadvantage of this logic? In what situation, can it go wrong?