Can I use Maaser money towards airfare to go to a friend’s wedding?
In the unusual case where there are not enough people to be Mesameach the Chosson and Kallah, as the expected norm, and it is certain that the Chosson / Kallah will indeed be made happy as a result, one may use Masser money towards travel expenses.
Nonetheless, one should still seek out to do this Mitzvah locally, where Tzedakah will not suffer from the expenditure. Likewise, one should attempt traveling through cheaper methods of travel, such as car, train, etc.
In the event where this isn’t possible, or even if possible, but one would otherwise not go, then one may use Masser money for airfare.
In the case of a poor family of a Chosson / Kallah, there can be more room for leniency.
ראה שו״ת בצל החכמה קסב, יח. קסג. ושם מחמיר יותר לשיטתו שבכלל מעשר כספים לעניים זולת באופנים המפורטים שם.