How do we actually perform our salah in the airplane without knowing the qibla?
You can pray in your seat facing directly ahead, since it is often difficult and inconvenient to pray out of the seat. And if it is possible and convenient, you can face in the direction of the qibla if you can determine where you are on the globe (some airplanes have a screen that shows your current location). If you know where you are, you’d face in the general direction of Mecca from that location.
Source: Ibn Baaz, fatwa 6293.