Possible reasons for roll when AP disconnects in ALT 2....
Fuel imbalance
Asymmetric thrust
Rudder position
Roll demand
Aileron or spoiler position
Icing
Any more, anyone?
And responding to
ventus45....
The autopilot would have been performing rudder inputs to maintain heading.
The autopilot uses bank angle to control heading. It applies rudder to maintain balanced flight. If this is done as yaw damping the rudder pedals do not move.
Would the rudder freeze there ?
No.
A few pages back, someone noted that Airbus pilots don't usually have their feet on the pedals in the cruise.
But once PF was flying manually in ALT 2 he would have his feet on the pedals.
Given that the BEA do make a point of emphasising the "continuous" left stick, and since they also emphasise there were no engine issues to support any asymetric thrust induced yaw
I must have missed this "emphasis" - can you point me at a quote from the BEA?
Is it possible, that simply failing to press that button to ensure the rudder was zero
If the pilot needs to adjust the rudder trim he uses the rudder trim switch. When the AP disconnects it is not a requirement to press the "zeroing" button.