This Halacha is an excerpt from our Sefer
Flying on Tisha B’av
May one fly on Tisha B’av if there is a need to do so?
Yes, however it is best to arrange for an afternoon flight.
If one is flying on a fast day and is extending or hastening the sunset, when is he to break his fast?
He is to break his fast as soon as Tzeis Hakochavim arrives in the area that he is currently in. Thus, if he flew from the U.S. to Israel and is hence hastening the coming of Tzeis Hakochavim, he may to break his fast as soon as Tzeis Hakochavim arrives on his plane. If, however, he flew from Israel to the U.S. and is hence delaying the time of Tzeis Hakochavim, then he is to fast until Tzeis Hakochavim arrives while he is on the plane. Some Poskim however rule that one may be lenient to break his fast in accordance to the area that he left from, upon Tzeis Hakochavim arriving there.
 Nitei Gavriel 79:9
 Igros Moshe 3:96; Betzeil Hachochmah 1:31; Chavatzeles Hasharon 1:43; Yaskil Avdi 8:31; Piskeiy Teshuvos 562:2; See Nitei Gavriel Bein Hametzarim 4:5
 Shevet Halevi 8:261; See Nitei Gavriel ibid