Pneumatic Calves' 5 foot flight speed with average mobility leads to some rather odd rules interactions. Average fliers can only ascend at best 60o
up and in doing so their movement is halved. So it could be done with a double move/full round action perhaps. However, due to average maneuverability requiring moving at least half one's flight speed in a round to stay airborne, even moving that 5 feet is impossible because half of that is 2.5 and that can't technically be done in D&D.
I suppose it could be done with the run action, but according to WotC
it has to be a natural flight speed, which Pneumatic Calves doesn't seem to be unless it gets changed.
DMG 20 has the info on the different flight maneuverability levels. The SRD also has it here