Ruler Of The Skies Achievement
Ruler Of The Skies5
Destroy 500 air units in combat
Campaign mission 2-4 is the best spot for air battles if done in the campaign. As always, you can verse other players in air combat with it being advised that you gravitate toward people with very easy or easy classifications to make things less damaging on your army. It helps if you work on bounties during this time as well, but the campaign mission is the best spot to grind out the kills.