Fortnite's airplanes, called the X-4 Stormwing, have been a controversial addition to the game ever since they were added at the beginning of season seven. No matter how you feel about them, though, they are needed to complete a variety of Battle Pass Challenges, like this time trial challenge from the season's penultimate week.
You will need to hop in a plane and fly through timed trials to finish out the challenge, and we've marked their locations on this map. One is found by the hero mansion south of Lonely Lodge, another is to the east of the hotel, and the last one is on the very southwestern tip of the island. Just fly through the rings as they appear in a timely fashion and you should be fine.