A lot of Islamic scholars have explained issues regarding fasting and traveling. As explained by Sheikh Muhammed Salih Al-Munajjid, these are the instances or conditions a traveler MUST meet before breaking his or her fast.
1. His journey should be lengthy, or else be known as traveling, and should go beyond the city and its suburbs. His journey should also not be a journey for sinful purposes (according to the majority of scholars), or for the purpose of trying to get out of having to fast.
3. Whoever is determined to travel in Ramadan should not have the intention of breaking his fast until he is actually traveling, because something may happen to prevent him from setting out on his journey. (Tafseer al-Qurtubi, 2/278).
4. If he is flying, once the plane has taken off and has gone beyond the city limits, he may break his fast. If the airport is outside his city, he can break his fast there, but if the airport is within his city or attached to it, he should not break his fast in the airport because he is still inside his own city.
5. If the sun sets and he breaks his fast on the ground, then the plane takes off and he sees the sun, he does not have to stop eating, because he has already completed his day’s fasting, and there is no way to repeat an act of worship that is finished.
6. If the plane takes off before sunset and he wants to complete that day’s fasting during the journey, he should not break his fast until the sun has set from wherever he is in the air. The pilot is not permitted to bring the plane down to an altitude from which the sun cannot be seen just for the purposes of breaking the fast, because this would just be a kind of trickery, but if he brings the plane down lower for a genuine reason, and the disk of the sun disappears as a result, then he may break his fast. (From the fataawa of Shaykh Ibn Baaz, issued verbally).
7. Whoever travels to a place and intends to stay there for more than four days must fast, according to the majority of scholars. So if a person travels to study abroad for a period of months or years, then according to the majority of scholars – including the four imaams – he is regarded as one who is “settled” there and so he has to fast and pray his prayers in full.
8. If a traveler passes through a city other than his own, he does not have to fast, unless his stay there is longer than four days, in which case he must fast, because the rulings that apply to those who are settled apply also to him
9. Whoever begins fasting while he is “settled” then embarks on a journey during the day is allowed to break his fast, because Allaah has made setting out in general a legitimate excuse not to fast. Allaah says (interpretation of the meaning): “… and whoever is ill or on a journey, the same number [of days on which one did not observe sawm must be made up] from other days…” [al-Baqarah 2:185
10. A person who habitually travels is permitted not to fast if he has a home to which he returns, such as a courier who travels to serve the interests of the Muslims (and also taxi drivers, pilots and airline employees, even if their travel is daily – but they have to make up the fasts later).
The same applies to sailors who have a home on land; but if a sailor has his wife and all he needs with him on the ship, and is constantly traveling, then he is not allowed to break his fast or shorten his prayers. If nomadic Bedouins are traveling from their winter home to their summer home, or vice versa, they are allowed to break their fast and shorten their prayers, but once they have settled in either their summer home or their winter home, they should not break their fast or shorten their prayers, even if they are following their flocks. (See Majmoo’ Fataawa Ibn Taymiyah, 25/213).
11. If he starts Ramadan in one city, then travels to another city where the people started fasting before him or after him, then he should follow the ruling governing the people to whom he has traveled, so he should only end Ramadan when they end Ramadan, even if it means that he is fasting for more than thirty days, because the Prophet (peace and blessings of Allaah be upon him) said: “Fast when everyone is fasting, and break your fast when everyone is breaking their fast.” If it means that his fast is less than twenty-nine days, he must make it up after Eid, because the hijri month cannot be less than twenty-nine days.