Originally Posted by
BraceBrace
1) we are talking about fly-by-wire systems. Boeing advises the use of A/T with A/P off on FBW aircraft. The statement "A/T OFF" is incorrect and applies to none FBW Boeing. On a FBW Boeing you are allowed to fly A/T off, but this is mainly done for proficiency and preferably in good weather conditions and otherwise standard operations (ie standard ILS approach into known airport).
Yes, there is a lot more to talk about regarding airplane design, we could spend several days debating.
I don't understand what you typed here. Which statement is incorrect ?
You mean having the A/T OFF should not be done, or a statement that I made regarding what happens with A/T OFF is incorrect ? If so, which one ?
Originally Posted by
BraceBrace
The PF is not supposed to look anywhere else for 10 seconds, especially not when he's reducing the speed. Why would he look anywhere else? This is basic piloting skills. Hence the question if you're a pilot or an engineer.
Of course the pilot is supposed to be flying the plane. "Supposed to"... An airplane that is more stable, is easier to fly.
In some fatal accidents, pilots have been seen not to look at their displays for "extended" period of times.
Eastern 401 is the most prominent example. Much more recently, prime air/atlas air 3591, one was disoriented, the other one wasn't properly monitoring.
Another very good example is Turkish 1951. The A/T retarded and it wasn't noticed until too late. All of these are proof that pilots are fallible at maintaining a perfect constant monitoring of flight parameters.
Hence, a stable aircraft is a better idea than one that you have to keep a very close eye on.
In this debate you could simplify or caricature my position as one of the following :
- advocating for airbus law without the speed in the FBW law
- advocating for an easier trim. Display the trim reference speed (I'm told that the A220 displays it, which I couldn't verify), or have a way to synchronise the trim with the speed, or reduce the stick force to make the unstable behavior slower...
Then, easy or easier is subjective.
Imagine you're flying the airplane on final, you know the power setting for this phase of flight. Usually around 55% on most jets. Imagine you perfectly matched your speed bug and your TRS.
Your plane should be stable, right ? Still not !
If you pitch down ever so slightly, the A/T will reduce the thrust to keep the speed. You will lose energy. When you notice the glide error (be it small or large), the thrust will increase to help you climb back to the glide, then decrease again. All of it is destabilizing.
If you flew A/T OFF, with the correct power setting, if you pitch down slightly, now your airplane will accelerate. Hence you now have a second cue on your PFD that you're low : the glide and the IAS. You can just pitch up, you will trade speed for altitude, and you will be back on the glide at the correct speed, without thrust variation.
Some people will find the first method easier, because they focus on one cue and don't have to worry about knowing power settings. Other ones will prefer the second method.