Gentlemen, - I think there may be a bit of confusion here.
Firstly - I am not talking about smooth conditions Autopilot off and maintaining straight and level.
I am talking in the event of an upset be it from an Overspeed event or wake turbulence or some such disturbance.
There is a key difference in Airbus from Boeing Heavy jets. (Again not wanting to start a boeing/Airbus feud)
The key difference is this-
All Wide body modern airbus have a trim tank that uses fuel. Fuel is pumped to the rear of the aircraft during the climb to move the centre of gravity aft to make the trim drag in the cruise less. This results in a marked decrease in longitudinal static stability. So as I have stated should one experience an upset at high altitude, best you leave that Autopilot engaged.
