Originally Posted by
safetypee
Vessbot, how do you recognise the need to disconnect ?
Are you able to describe the process which you use, which will always apply in every situation. If this starts with understanding the situation, then how do you understand.
To you it might be obvious, to others no so depending on the situation, experience, training - even of this can be trained at all.
The criteria are very clear.
Aircraft trajectory deviated, deviating, or even about to deviate from the prescribed and safe track. The deviate, deviating or about to deviate depends on the pilot's capacity to detect the problem as soon as possible.
(For very minor deviations, the automation could be kept on. I heard of a case where the AP descended below the minimum altitude, but it was 2450ft instead of 2500ft. In clear blue sky it could be discussed that it is more interesting to observe the aircraft as long as it is doing something safe (once again : VMC) and be able to describe the problem in more details to the manufacturer, so that the system can be improved in the future)
One could even say that if there is even a mere potentiality that the system might misbehave : automation mode can be changed or even disconnected (if it is deemed safer to manually control the aircraft than to risk the aircraft doing something unexpected)
Some well know criteria are : descend below safety altitude, deviation of more than half a dot on loc or glide, or half deviation of the vor scale, 0.5nm for a dme arc, etc..
Other well know criteria are speed below Vls (airbus world) or alpha above alpha prot, there is no well-known figure for beta (sideslip), I think because the figure would be 0. Since aircraft are yaw-stable, any deviation is caused by a large external force (engine failure, aerodynamical problem..) which require immediate correction.
You could also put a limit at 33° of bank and debate of a figure for negative Vs. Some say "one minute before touchdown at all times"
The process that is used and trained is to monitor the aircraft. Speed, pitch, power, bank, altitude, radionavigation, all these are monitored constantly. The whole point of training is to know what to expect, how to achieve it, in a light aircraft. In a large aircraft it is exactly the same except it is more often achieved by the flight guidance system on the pilot's orders rather than manual inputs.
Originally Posted by
FullWings
Vessbot,
That’s a couple of very cogent posts, dense with some really good observations.
For me, having had a fairly long career in aviation but coming from an engineering/science background, one of the (many) issues that gets me is the user interface that a modern commercial transport presents to its operator. In a word: suboptimal. They are an unholy mix of a century’s worth of ideas and technology, keeping the bad as well as the good for some kind of continuity. IMO many EFIS+FMC presentations are actually worse for SA in some areas than an equivalent steam-driven setup: un-annunciated hidden modes, weird logic and a plethora of known but too-expensive-to-fix bugs in prehistoric firmware/hardware.
Suboptimal : yes.
One very interesting aspect is flight at high altitude.
Yes, people are not supposed to be flying manually at high altitude. But many accidents have happened there. So pilots should still have an optimized interface.
Suppose your aircraft is on its way to cruise flight level 380. At flight level 372, AP disconnects. What are you going to do ? Suppose the best course of action at this time is to stabilize, first, at FL380.
Say you climb at 800ft/min, speed is about 450kt. You just have to push the nose and stabilize the aircraft. The pitch change required is about 1 degree.
But which instrument do you have to control this ?
https://lh3.googleusercontent.com/pr...30Dzx6K4Hkrabg
From what I read, the center square on the PFD is about 1.6° large, and each pixels is about 0.2mm large
Between +10° and -10°, there are 4cm. That is 2mm per degree. And the center square is about 10x10 pixels. So the pitch change required to go from climb to cruise, or cruise to climb is about half the size of the center square and 1mm. Now look at a ruler with millimiter markings and ask yourself if it's easy to differentiate them.
It leads to something like this :
In climb, the top of the bottom segment of the center square is aligned with the top of the 2.5° line.
To go from climb to cruise, you have to put the bottom of the top segment and align it with the top of the 2.5° line.
This is a variation of about 0.8° so a realistic value for a heavy day.
It is absurd to think a normal human being can easily control something so tiny.
If Airbus really wanted to make possible manual flight at a high altitude (for cases of automation failure) they should implement a button that could be used only at high altitude which would switch the aircraft in "high precision mode".
- The PFD would be magnified at least 4 times. There is no point in seeing +/-20° in cruise as is the case on the above picture.
- The flight controls would also have a reduced efficacy (not sure about this one though, just a possibility, in my opinion the sidestick is too small even for low altitude flight so...).
There is the same kind of problem on the thrust levers.
When you want to begin taxi and apply breakaway thrust, let's say 30%, there are a few centimeters of dead area. So the thrust lever course, which was not very long to begin with, is even more reduced by this. On final approach, a variation of just 1% corresponds to almost 100ft/min.
I did not measure the distance to be traveled to change the thrust by just one percent... But my guess is it is about half a millimeter.
I don't get it. The aircraft is huge, there is plenty of space in the cockpit, but you have to move the thrust levers and the PFD target by distances similar to that of an ant's arse !
It seems that I completely agree with you overall.
The idea of giving airline pilots a few hours every now-and-then in a light aircraft to get the old scan and handling ability up again often comes around and is generally pooh-poohed as being impractical, expensive,
Which is exactly what I'm doing, at my own cost obviously. And if it is indeed pleasure, it surely helps.
At one point during the covid crisis I wasn't flying much on the airbus. To get myself going again, I booked a flight on a small aircraft. I did 15 short circuits followed by landings. All were full flaps and idle power. This gives a descent rate that is close to what you get on the A320, so it was good practise, my landings were definetely better that without this.