I have created a custom airport by following the instructions of the example.txt file, most of the functions worked properly, but when I created a scenario for my custom airport, I found out that all the planes generated in the scenario wouldn't perform according to the planetype information I set up in the file. I wonder why it worked the way it did, and hopefully there will be a solution for this.

Hi. Perhaps writing the planetypes in lower case fixes it. But it's hard to know what causes the issue without seeing the actual file. If you have Discord you could probably get more help from other content creators there. Good luck.