Originally Posted by
maddogmax
Can't remember about the 320 but on the 330 there is a limitation that says you cannot operate the packs and external air at the same time. Also, most times it is not that easy to get external air disconnected unles you do it yourself.
No such limitation on the MD (that I know of
). Ground air enters in the mix manifold downstream of the packs so the presence of ground air has little, if any, affect on the operation of the packs.