A person is not allowed to break their fast until they are sure that night has fallen, by either checking themselves through the window or asking the pilot whether it is night in the local zone that you are flying over. For example, if a person is flying from Sydney to Indonesia, a person must wait until you see the night falling in the local zone before they can break their fast regardless of whether or not it is night in Sydney.

How do you know when its time to iftar on a plane? from Al Mahdi tv on Vimeo.