Answer: The Mishna (Taanis 26b) writes that from when the
month of Av begins until after Tisha B’av, we reduce in our enjoyment. The
Shulchan Aruch (OC 551:2) lists a few restrictions that must be observed during
these nine days. The Noda Biyehuda (OC 2:105), however, writes
that one should also avoid other activities that one enjoys during this time. Thus. R’ Shmuel Wosner (Shevet Halevi 10:26) and R’ Ephraim Greenblatt (Rivevos
Ephraim 1:374) write that one should avoid going on outings during the nine
days.
The Shulchan Aruch (OC 551:18) writes
that one should also avoid doing anything potentially dangerous during the three
weeks. Following this, R’ Shlomo Zalman Auerbach (Halichos Shlomo, Bein
Hametzarim 14:24) writes that one should avoid flying during the nine days.
While flying is considered a safe means of transport, one still says the beracha
of hagomel afterwards due to its potential dangers.
Nonetheless, R’ Auerbach allowed yeshiva
bachurim learning in Eretz Yisrael to return home during the nine
days rather than leave yeshiva earlier. Likewise, he maintained that
it is permitted to fly to Eretz Yisrael during the nine days, and
if necessary, even on Tisha B’av (afternoon).
In conclusion, while one should avoid
flying during the nine days, one may travel to Eretz Yisrael then.