[m463]

My friend had one, and it would generate oxygen, and simultaneously fill a portable tank for going out.

I don't know the protocol for air travel - do you generate O2 with a device during your travel or carry an oxygen tank?

I could imagine scenarios where a pressurized tank on an airline is bad, and also scenarios where a device would be bad too.

I've also heard of people that had medical conditions and they just weren't allowed on the plane at all.

[cameldrv]

Oxygen concentrators are allowed, but they have to be FAA approved, you have to have a prescription, and they have to be battery powered (you can't plug them into the seat power).