Instructions
Drive to the marker set on your on-screen map. This will take you to a vacant airplane on a runway.
Press the triangle button to exit the car. Walk up to the plane and press the triangle again to enter the plane.
Hold down "R2" to accelerate the plane. Pull back on the left analog stick to raise the plane into the air.
Fly the plane toward the new marker on your map. After you reach the edge of the map, a cutscene will play where you and another character are at Saint Mark's Bistro. After the cutscene plays, you will be returned to Los Santos. The mission will complete and Didier Sachs will be unlocked.