Here is the full list of all 22 AX:EL - there are Air XenoDawn achievements.
Send 1000 enemies to the "otherside"
Complete Mission 10 in a special way
Complete Mission 10
Complete Mission 9
Complete Mission 8
Complete Mission 7
Complete Mission 6
Complete Mission 5
Complete Mission 4
Complete Mission 3
Complete Mission 2
Complete mission 1
Destroy 500 enemy vehicles
Kill 250 enemies
Visit the hub 250 times
Visit the hub 100 times
Shoot down 100 enemies
Kill 50 opponents
Visit the hub 50 times
Shoot down 10 enemies
Kill your first enemy
Visit the hub.