A330/340 maintain straight and level.
A320 will go into a slight climb.
With no input on the sidestick you are commanding 1 g. At altitude g is less than 1 so to maintain 1 g it has to climb slightly. A330/340 the software accounts for this but not in the a320 family.
Last edited by fmgc; 7th Dec 2012 at 16:46.