السلام عليكم و رحمة الله و بركاته، احسن الله إليكم When travelling via airplane, if the flight will result in missing multiple salawat should one pray them all before getting on the plane or should pray in the plane? Also if sitting in plane is salah valid since rukn of qiyam is not fulfilled?

Ustadh AbdulAziz al-Haqqan

No this is forbidden. You should only combine thuhr and asr or maghrib and isha' for example, and if u will miss the time for both the salahs then u pray on the plane standing up facing the qiblah to the best of your ability. If it is not possible then you pray sitting down and Allah knows best.