You have one of two choices:

1- First option is to assume ihram when they announce the approach of Miqat in the plane. If you are travelling by Saudi airlines, they have a musalla where you can change into the ihram attire; in case of females, they do not have to go through this requirement as they are allowed to wear their regular attire.

2- The second option is to assume ihram after landing in Jeddah:

If assuming ihram in the plane is not possible, then you can postpone ihram until you arrive in Jeddah. As ruled by some of the eminent scholars of the past and the present, those who travel by air or ship are allowed to assume ihram in Jeddah.

 

Almighty Allah knows best.