Instructions
Complete the main story missions in Los Santos, Red County, Badlands and San Fierro. You will unlock the Desert and Las Venturas, gaining the ability to perform missions for Mike Toreno. Complete his first mission, "Interdiction," and Toreno will ask you to purchase the Verdant Meadows Aircraft Graveyard as part of his "Verdant Meadows" mission.
Head over to the Verdant Meadows Airfield in the Desert. Buy the Aircraft Graveyard for $80,000. This purchase will complete Toreno's "Verdant Meadows" mission and unlock the Verdant Meadows Flight School in the control tower.
Complete the "Learning to Fly" mission at the Verdant Meadows Flight School. The mission is made up of ten tests that will assess your flying ability. Achieve a score of 70 percent or better on each test to continue. After you've passed all ten tests, the airports will be open to you, unlocking all of the airplanes inside.