Is it okay for people with sickle cell to fly on the airplane?

Flying w sickle cell: Yes it is. Like anyone else on the plane, if you're flying for long time, make sure you get up and move around. For long trips, there is a risk of deep vein thrombosis so the airline actually recommends you move your ankles in clockwise and then counterclockwise fashion. Like wax-on, wax-off for your feet. That was a karate kid reference if you're a young person and never saw the classic film.

Depends: A person with sickle cell disease is at higher risk of a sickling episode. If the person has sickle cell trait, it should not matter in a commercial flight with pressurized cabin.