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.

Wassalam.