For this mission you'll need a truck or a van. To start the mission head over to the current city's airport and start the mission by entering the checkpoint and typing the command /robbery to start the mission.
After a couple of seconds of breaking into the airport, a timer will show up. In this time you'll have to get out of the truck/van and collect boxes. The more boxes you collect, the more money you'll recieve at the end of the mission. Beware that during this time you will be wanted, so you'll be an easy target for nearby officers.
Boxes can be put in the truck/van by pressing the Middle Mouse Button or by typing /box. When the time is over you'll have to get back into your truck/van. Once you get in the vehicle you'll see another timer appear which indicates the time you have left to get to the hideout.
Once you reach the hideout, you will recieve your payment. If no cops are nearby, your wanted level will also drop.
Type /cancel at any time during an Airport Robbery to cancel the current mission.