This mission will begin at Michael's house, which is marked with a "M" on the map, and must be started by Franklin. After a short conversation, the game will switch to Michael and then to Trevor after the cutscene finishes. Drive your way to the hangar and get inside the Duster. Take off and make sure you stay as low as possible to the ground, as you don't want to trigger your position on the radar.
Eventually, you'll spot the cargo plane in the distance, but you'll still need to stay low as you follow it. Should you get too high, Ron will warn you and you'll need to get lower again. Also, when you fly close to the military base, do not fly over it. Keep following the plane until you get out of the military zone, which allows you to gain altitude.
Fly higher and straight towards the tail of the plane, ignoring the warnings given by the Merryweather guys. As you get close, they will open up the door and begin firing at you. Just keep going straight into the plane and Trevor will make a "nice" landing. You must now fight your way towards the cockpit of the plane, making sure you use cover to hide.
When you finally clear all of the guys inside, climb the ladder up to the cockpit and shoot the pilot. Commandeer the plane and start heading towards the new marker, only to have military jets come and ruin the party. Ignore them and fly higher as Ron says, but they eventually fire missiles at you, blowing one of the plane's engines.
Keep flying until the game switches to Trevor inside, where you will need to run to the door and jump out. Skydive towards the ground and open the parachute whenever you feel like you need to. The plane will crash into the nearby waters, but there's nothing you can do about that now. The mission will end whenever you land on the ground.