وعليكم السلام ورحمة الله وبركاته

It is not permissible for a woman to travel without a maḥram, regardless of whether the journey is short or long, by car, plane, or any other means. Ibn 'Abbas (may Allāh be pleased with them) reported: I heard Allāh's Messenger (ﷺ) delivering a sermon and making this observation:" No person should be alone with a woman except when there is a Mahram with her, and the woman should not undertake a journey except with a Mahram." A person stood up and said: Allah's Messenger (ﷺ), my wife has set out for pilgrimage, whereas I am enlisted to fight in such and such battle, whereupon he said:" You go and perform Hajj with your wife." [Sahih Muslim, 1341] The scholars have explained that this prohibition applies to all forms of travel that are considered “safar”, and that the texts do not differentiate between one hour and several days. Additionally, the reasoning behind this ruling is not about the dangers of travel alone per se, but about obedience to a clear and general prophetic command that applies regardless of modern transport safety. ------ Sheikh Ibn Baz rahimahullah said: "It is not permissible for a Muslim woman to travel by airplane or by any other means without a maḥram accompanying her during her journey, due to the generality of the statement of the Prophet ﷺ: “A woman must not travel except with a maḥram” — agreed upon. This is because it is possible that she may be exposed to harm during the flight in one way or another, so long as she has no one to protect her. Another matter is that airplanes sometimes encounter malfunctions, causing them to land at an airport other than the intended destination, and their passengers may have to stay in a hotel or other place while waiting for repairs to be completed or for another aircraft to be arranged. Such delays may last a long time — a day or more — and in this there lies the risk of the woman traveling alone being exposed to harm. In summary, the wisdom and benefits of the rulings of the Shari'ah are many and great, and some of them may be hidden from us. It is therefore obligatory to adhere to the textual evidences of the Sharīʿah and to beware of opposing them without a clear, certain legal justification. May Allāh grant everyone understanding in the religion and steadfastness upon it. He is the best of those asked. And peace and blessings be upon you." Source: https://binbaz.org.sa/fatwas/14047/%D8%AD%D9%83%D9%85-%D8%B3%D9%81%D8%B1-%D8%A7%D9%84%D9%85%D8%B1%D8%A7%D8%A9-%D9%81%D9%8A-%D8%A7%D9%84%D8%B7%D8%A7%D9%89%D8%B1%D8%A9-%D8%A8%D8%AF%D9%88%D9%86-%D9%85%D8%AD%D8%B1%D9%85