The Flight School is an addition available after downloading free DLC. This activity is very similar to the one that can be played in single player mode. However, here you will be faced with the 'military' challenges which are the hardest challenges. It is a great possibility to earn money and experience. It also enhances your flying skills.
The tasks can be repeated, but then you will get only about 10% of the former reward. Acquiring gold medals equals the payment of 10-30 thousand dollars as well as 1-2 thousands of experience.