Jewish Law Faces Challenges Over Fasting Times for Air Travelers Crossing Time Zones

The rise of international air travel presents a complex halachic challenge regarding the fasting times for Jewish passengers, especially during fast days like Tisha B'Av. The core question is whether a traveler flying westward must fast continuously for up to 33 hours, following the local sunset times of their departure point, their current location above the earth, or their destination. Traditional Jewish law, as stated in the Shulchan Aruch (Orach Chaim 625:2), mandates that a person who moves from a place where fasting is not observed to one where it is must fast according to the local time of the destination until nightfall there. Most contemporary halachic authorities agree that "your place and your time" determine the start and end of the fast, meaning the fast corresponds to the geographic location of the traveler at each moment.

For westbound flights, this can significantly extend the fast, as the traveler "chases" the sun, potentially fasting beyond 24 hours. The stringent view, supported by Rabbi Ovadia Yosef and the "Igrot Moshe," requires fasting until nightfall at the traveler's current location, even if it exceeds a full day. Conversely, lenient opinions like those of the "Pri Eliyahu" and "Yashkil Avdi" allow breaking the fast after completing the required fasting hours based on the departure location, even if the traveler is still in the air.

Rabbi Vazner offers a compromise: after completing the fasting hours of the departure place, the traveler is considered ill and may consume necessary food until the fast ends at the destination. Medical experts warn that prolonged fasting on flights, which can last up to 33 hours, poses health risks such as dehydration and blood clots due to immobility and dry cabin air. They recommend walking every three hours on long flights and permit small amounts of water if health is at risk after the initial fasting period.

For eastbound flights, such as from the U.S. to Israel, the day shortens, and the fast may end sooner. According to the "Igrot Moshe," one may break the fast at nightfall in Israel even without completing a full 24-hour fast. However, Rabbi Moshe Sternbuch insists on completing a full 24-hour fast on Tisha B'Av regardless. Overall, while the traveler's current location generally determines fasting times, halachic authorities allow leniencies in cases of long flights and health concerns, especially before landing. The issue remains complex and often requires rabbinic guidance.