The air pressure within the cabin of a commercial airplane is not the same as the air pressure at sea level. This means that when you travel by plane, oxygen will not enter your body as easily as it does normally.
Anyone travelling in an aircraft will have a drop in the amount of oxygen getting into their blood, although they are unlikely to feel any different.
When you have a chronic lung condition this can make your chest symptoms worse. You may feel more breathless, your chest may feel tight.
The longer your flight lasts, the more likely you are to experience symptoms.
With the right medical advice and precautions, very few people experience problems when they fly.