Credit goes to DROGTURIST.
You need to score 9 consecutive kills without dying. The best way is to:
- Choose Enlist Now, Local Multiplayer, Game Setup
- Choose the Lost Island map, 15 kills, 10 bots, Cadet difficulty.
- Choose a Heavy plane with any weapons you like.
As soon as it starts, look for a turret and get in there (the white crosshair on the map). Use RT for Machine Gun or LT for Cannon. The cannon will take out enemies almost instantly. If a plane starts hitting you (you can see your green health bar go down), leave the turret with Y, do a 180 loop, and come back in it. When you get 9 kills, the game will tell you. You can stay in for the remaining 6, or you can leave the turret and work on your kills with a particular weapon.
When the game ends, do another one just like it until you get the reward 10 times. The Achievement page on the Menu will tell you your progress on all achievements.