Can a woman travel alone, if the journey is less than 24 hours and is by plane?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

A woman is not permitted to travel without a Mahram (husband or unmarriageable male relative) for the distance of 83 km, whether she travels by air or any other means.

Furthermore, passing through the distance fast or slow has no effect on the above ruling.

In this vein, the Prophet said: “It is forbidden for a woman who believes in Allah and the Last Day to travel for a one-day and night-journey without a Mahram.” [Al-Bukhari and Muslim]

For more benefit on the prohibition for a woman to travel without a Mahram, please refer to Fataawa 262621, 88562, 193077, 102095, and 85945.

Allah knows best.