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