Is it permissible to pray on an airplane or in a car during long journeys, and what is the ruling on praying Maghrib and Isha when traveling westward while the sun is still shining?

It is not permissible to pray Maghrib or 'Isha on an airplane as long as the sun is still out, even if their times have begun according to your country's local time. This is because the time for Maghrib begins with the setting of the sun, and similarly for Dhuhr and 'Asr. Therefore, one must adhere to the Sharia (definition)-based signs for the beginning of prayer times.