what untreatable illness, doesn't allow person for air travel for life?

is there sickness, or medical conditions, disqualificating a person from flight by airplane?

Check with travel.state.gov for that one. I'm guessing HIV or something along those lines that could be deadly wouldn't be allowed into another country. But I could be wrong.

No. There is no illness that bans a person from air travel for life. People with highly communicable diseases (airborne infectious diseases) naturally should not travel on an airplane - such as they shouldn't be in any enclosed space with other people while they are sick.

I would have to say leprosy and tuberculosis.