From an old pilot. Two things: 1. The cabin altitude of an airliner flying in the 25-35 thousand range is normally 8,000 feet. i.e. the air is much thinner. Anyone flying in an airplane is not going to get the normal oxygen they would at sea level or living at 2 or 3000 feet. This will then affect everyone to some degree and us with lung problems even more so. 2. With the exception of some very new models most commercial airplanes must recycle the air in the cabin. No outside air is added. Therefore, any desease or bugs of any kind can easily be spread. Because of this, some doctors will advise their patients to only fly when absolutely necessary. My 43 year old son has CF and does fly on occassion. I have COPD and my doctor will not allow me to fly without oxygen. You can't bring your own in the cabin and must use the airlines. Not all airlines will even provide it. It currently costs $75 per leg. My son lives in Texas (I'm in Virginia), so when I go to see him I have only 2 choices. Delta, thru Atlanta (2 legs) or $150 and $150 return, or Continental, which has a non-stop flight and oxygen for a round trip ticket would only be $150. Going back to item 1. When I have to go to the rest room, I can't take the oxygen, so by the time I make the short walk there and back, I need the oxygen badley!