Think we fly for the same opperator OY and I was wondering whether switching them on with the engines going amost full pelt does the packs any harm?
When we do packs off, which is only when performance requires, we switch the first pack back on after thrust reduction. We switch the other pack back on after flap retraction.
Why after flap retraction, I don't know? Perhaps that's just a convenient memory jog to do it, and it is long enough after the first pack on so to avoid a possible pressure surge which the system would experience if both were turned on at the same time.