First, one should strive to do the prayers while still on the ground rather than pray them while in the air even if it means combining the prayers according to the rules of combining in the madhab.
If they’re unable to, they should ask permission of the stewards in the back, face the qiblah as best as possible and pray the prayer as fully as possible with the rukū’ and sujūd.
Khalil says “(It’s necessary) as long as one is safe (and able)…to face the direction of the qiblah.”
And he says “It is necessary in a fardh prayer to stand except if it causes hardship.”
One hardship might be turbulence during the prayer time or the airline not allowing prayer, so if they’re still unable to do that within the prayer time at the back they can do it at their seat without facing the qiblah.
They should try to stand in all the areas standing is prescribed in the salah. For the rukū’, they should lean slightly from the standing position. For the sujūd they should lean over while sitting down.
Written by Ustadh Tariq Patanam. Approved by Shaykh Rami Nsour.