The frequency of crisis seen is extremely variable and every patient has a consistent pattern. It is important for you to know the environmental triggers that set off crises in you. These often include exposure to cold temperature, dehydration, stress, too much exercise etc. Low oxygen tension causes the cells to sickle but most aircrafts are pressurized so that is usually not a problem if the flight is about 6 hours or so. See if you can break journey in between so that your continuous flying time is reduced. Drink plenty of water in the flight and cover yourself well so that the air conditioning doesn’t make you feel cold. While in the U.S., dress yourself in layers to keep yourself warm as cold temperature can trigger a vaso-occlusive crisis. Also speak to your treating physician who will be better placed to advise you.