They do, but not very well.

Usually I only see nemesis start AI use air forces at all. Many majors decide not to build air forces and use only ground based air defenses. I heard it's supposed to be 50% chance a Major builds air forces but either I'm really unlucky or it's less than that. Even when ...

I'm playing on Hard too, so I think the AI is failing to ever develop air forces when it starts at tech 3.

Are you using a higher starting tech level? Which difficulty settings?

I've been starting on tech level 3 meaning they would have to research the tech before they can build an airforce. I see every AI major choosing to rely entirely on anti-air and never build air forces even when they have time to deploy advanced technologies like laser weapons.

<t> I've played several games since the air forces were introduced and have yet to see any AI major build an air base or air unit. Only nemesis AI makes any use of air forces and it seems like that's only because they start with one. Nemesis AI does not seem to expand or replenish their air force ...