Since 2.7 update the only aircraft available in the Mission Editor is the F-15C and SU-25T. I have installed the basic A-10A, A-4E, F-22A, T-45.
Those aircraft were available in the Mission Editor prior to the update but now are not. The fact that the A-10A is not there is particularly puzzling.
(This is not the case in Open Beta. They are all available in Open Beta.)