The Sky Fortress Pack Add-on for Just Cause 3 has 7 achievements.
Use the Bavarium Wingsuit to take off from water.
Defeat the "Old Friend" (Boss at the end of "Taking Control").
Earn at least 1 Gear in all Challenges of the Sky Fortress Expansion.
Use the Barrel Roll to evade 10 incoming missiles.
Defeat 1 of each Drone type.
Beat the last mission of the Sky Fortress Expansion and complete the story arc.
Earn 5 Gears in all Challenges of the Sky Fortress Expansion.