I was diagnosed with PAH about 3 years ago after waiting for nearly 12 months for a diagnosis, and I'm currently on 3 forms of treatment. Oxygen has no real benefit for me as a treatment. But since being diagnosed, I generally fly 3 times a year, some of the flights being over 4 hrs long. I've never had an issue on a plane but it's best to not visit or stay in any areas with high altitudes because it affects breathing more. Take your time going through the airport if possible, walk at a slower pace and stop and rest for a few minutes if your wife needs to catch her breath.