Oh well did not want to get the books out but as someone mentioned what I was saying was incorrect and then corrected it with a common misconception I thought I better had.
Uplinker.
In my explanation when I was mentioning changing from MACH/SPEED I was not talking about managed or selected. Like I stated, the little black button that flips from MACH/SPEED.
Selecting a MACH number does not take it out of soft mode, you have to select a SPEED. It is also nothing to do with altitude variations.
From the FCOM:
When the aircraft is in ALT CRZ mode with the autopilot engaged, autothrust engaged in
MACH
mode, and is within a 3 kt range of the target speed, the autothrust soft mode engages. This
mode reduces the thrust variation in cruise specifically in light turbulence. The autothrust soft
mode disengages when the speed deviation from the target becomes too large or the target is
modified ; autothrust transition from soft to basic mode may lead to transient thrust variation. This
mode is inhibited with speedbrakes extended, or with engine out or when Mach target is below
0.65.
What actually happens is that in managed speed, (speed button PUSHED = magenta speed bug), the aircraft will allow altitude variations of +/- 200' in order to avoid 'hosing' the engine's thrust up and down to maintain speed. This is the so-called soft altitude hold
It actually does not do this. The AUTOPILOT maintains the level accurately and there is no such thing as soft altitude hold. After looking in the FCOM it turns out it is called A/THR soft mode. If a +/- 200ft variation was allowed do you think this aircraft would be certified to fly in RVSM? What if its altimeter was at the limit of the allowed error and it was meeting another A330 coming the other way with its autopilot allowing 200ft in the other direction with its altimeter out by the limit the other way. How much space would this leave between the two A330s?