So i've got what I think is a dumb question, but it's been niggling at me. You've mentioned airbus (and i'm guessing others) controls essentially dissengage when autopilot is active, ie they don't move with inputs from the autopilot. So what happens when you turn off autopilot? Is the position of the controls matched to the postion of the control surfaces in some way? I'm thinking with the talk before about autothrust, if you essentially had the controls at idle but autothrust was set at 50% (not sure if this is possible) if autothrust disengaged how would you be able to throttle back manually? Similarly if the plane was banking right and you disengaged autopilot given your controls would be centred would the plane right itself rather than continuing the bank? I really hope that question makes enough sense.
Firstly, no question is dumb. I've regularly had to go back into the manuals to answer what has been asked here....
Airbus and Boeing have a basic disagreement here. In a Boeing, the controls all continue to move with both the autopilot and the autothrust, whilst in the 'bus the joystick just sits there, and the thrust levers sit in a gate and don't move.
When the time comes to disconnect, the Boeings' controls will always be in the right place, so just disconnect and hold them wherever they happen to be, and the transition will be smooth.
The Airbus...well you should make sure that it's not actually 'doing' anything when you disconnect the autopilot. 99% of the time the disconnects occur when wings are level on an approach. Its basic rules are a bit different to a non FBW aircraft...if the aircraft condition is stable (i.e. a level 20º turn) then the joystick would actually be centred anyway. As long as it's not in the process of changing anything, then again, there is literally no transition. Press the A/P disconnect, and don't move the joystick...nothing changes.
Autothrust is different, and it is a gotcha. In a Boeing, the levers are always matched to the power output. There are no gates. When you select TO/GA, the levers motor to the end of their travel. The 'bus, on the other hand, has a couple of gates. From 'IDLE' to 'CLB' is about 95% of the travel, and only comes into play when using manual thrust. Above climb is 'MCT/FLEX' and then 'TO/GA'. If the lever is at TOGA, then the autothrust has no control of the system. If it's at MCT/FLEX, the autothrust only has control if you have an engine out, otherwise it gives you the FMC generated FLEX power. At CLB and below, the autothrust has control, with the lever position limiting its ultimate power. There is little to no reason to use less than CLB with the autothrust still engaged, but that's how it behaves.
Now, to disconnect the autothrust Airbus have installed some nice little red buttons, which happen to be right under your throttle thumb. These are called the 'instinctive' disconnect buttons...but, don't press them. If you do, the power will immediately go to wherever the levers happen to be (99% of the time in the CLB gate). First, you must always pull the levers out of the gate, to match the power with what you're actually using...and then you press the buttons.
