How do you get a plane license on grand theft auto San Andreas?

Answer 1

you have to unlock the desert on beat the pilot school

For more details, perhaps these notes will help:

During his missions working for Mike Toreno, CJ will get a phone call from Toreno telling him to purchase the old disused airstrip at Verdant Meadows in Bone County. Once CJ has bought the airstrip, he is able to enter the Flying School office. There he will get another call from Toreno telling him that he needs to learn to fly and how to get started on the lessons. To pass the Flying School missions, CJ has to get at least a bronze pass on each lesson. CJ will be given instructions on how to fly the aircraft he has to use, and once he has completed all the flying missions, he will have his full pilot's licence with access to all airports in San Andreas. This will also enable him to fly the planes and helicopters situated there. There are other aircraft available in the game which he can use of course, for example, there is a Sea Sparrow chopper situated on the waters in the Sherman dam area and a chopper parked on the beach in Los Santos.