As you play through the game, you will encounter schools for the various types of vehicles you can drive. There is a school for Driving, Boating, Biking, and Flying, with each one offering tutorials on various mechanics regarding the type of vehicle. During the course of the main story, you will have to do the Flying School in order to progress, so that means you cannot miss this trophy/achievement at all. Note that you only need to get a Bronze medal in order to pass the school, so there is no need to worry about getting Gold in any of the tests. All getting Gold does is spawn an extra vehicle or two for you to use outside of the respective school. Note that getting Bronze on all of the tests for each school is required for 100%, so even if the Flying School wasn’t required for the story, this would be unmissable if you were going for 100%.