The Qibla (Arabic: قِـبْـلَـة, "Direction", also transliterated as Qiblah, Qibleh, Kiblah, Kıble or Kibla), is the direction that should be faced when a Muslim prays during Ṣalāṫ (Arabic: صَـلَاة). It is fixed as the direction of the Kaaba in the Hejazi city of Mecca. Most mosques contain a wall niche that indicates the Qiblah, which is known as a miḥrâb (Arabic: مِـحْـرَاب).
We must try to perform our obligatory Prayers (Salah) where ever we are including in an airplane. We must try to find a suitable place to stand for few minutes to pray.
The direction of Qibla can be known through the cabin crew who usually ask the pilot about the direction of Makkah. You can also see the map of the journey and check where is Makkah from your flight route. There are also Qibla applications which can help.
In case you have no way at all to know the Qibla direction, you must pray facing any direction. After praying towards any direction which is obligatory , it will be recommended (not obligatory) to pray towards the other three directions.
If you are for any reason not allowed to stand to pray in the airplane, you should pray in sitting position on your seat.
The main point here is that the obligatory Prayers Must be performed in the best possible way within its time and it is not allowed at all to leave praying the obligatory Prayers till its time goes away.
If there is no way to find the Qibla direction then praying to one direction is enough but according to Mustahab precaution if you have enough time you may pray 3 other prayers to the other 3 directions.