I haven't had any issues using my CPAP on AA, BR, DL, OZ, JL, KE or UA. All I've had to do is tell the Lead or the Purser I'm going to use it and a couple of times they've checked my machine for the aircraft approved markings on the name plate. Usually they don't even do that and I've been told that it isn't really a issue for them as long as the hose or cord doesn't block aisle access. Not usually and issue since I'm almost always in either J or PE window so no issue with sticking the machine itself out of the way. If I'm in cattle upstairs on an A380 I just put the machine either in the storage bin or on top of it.