How can I pray on an airplane when the direction of the Qibla changes during the flight?

One must face the Qiblah in obligatory prayers, based on the Almighty's saying: (So turn your face toward Al-Masjid al-Haram. And wherever you [believers] are, turn your faces toward it [in prayer]). One can ask the flight attendants to determine the direction and pray standing while facing the Qiblah when the plane is stable. If it is possible to delay the prayer until after landing without its time expiring, so you can face the Qiblah while standing on the ground, then do so. If that is not possible for fear of the prayer time expiring, then pray according to your situation on the plane, and your prayer will be valid, for Allah does not burden a soul beyond its capacity.