.........and eat and drink until the white thread become the distinct to you from the black thread of the dawn. Then strictly observe the fast till nightfall) (Al-Baqarah 2:187)
"Anyone in a high place, like the Alexandria lighthouse for instance, is not to break his fast until he sees sunset, but the people in the city are to break their fast when the sun sets in the city. The same is applied in the sunrise as regards the Fajr (Dawn) Prayer and the predawn meal." -(the prominent scholar Ibn Abidin al-Hanafi author of al-Fayd) -
Quoted by Syeikh Yusuf al-Qaradhawi while clarify the same ruling should be applied to PLANE TRAVELERS who fly many miles away from the earth, as well as to those who live in mountains and high buildings.
They have their own dawn time, sunrise time, and sunset time. Therefore, when dawn appears to them on the horizon, they must begin fasting and pray Fajr; they must not pray Fajr before that or eat or drink after that.
The same is applied in the sunset: airplane passengers are not permitted to pray Maghrib or break their fast according to the time of the country over which they are flying. But they should eat, drink, and pray Maghrib after seeing the sun setting with their own eyes.