Question:  

Will salah be necessary on a traveler when the plane is flying in the air? If he performs salah in it, will his responsibility be lifted?
Answer:   حامدا ومصليا ومسلما

When the plane is flying the ruling is the same of a ship when it is sailing. That is, salah will be valid in it out of need.

كالصلاة على الدابة احسن الفتاوى 4:90

And Allah knows best.

Hazrat Mufti Ahmad Khanpuri Saheb (May Allah preserve him) Mahmoodul Fataawaa 1/471