An old favorite. And I mean really old. You have to use Dosbox or a similar tool to play, it runs under DOS! (not Windows) Fortunately the DOS emulators work well. The UI is a mix of mouse clicks and keyboard shortcuts. I like the kind of simulator action where you build you own empire of airports and air routes and try to out-compete the AI competitors. If you try it and have trouble in the first years there is an option for easy first 3 years that you can select.
TIP: at the start you can only afford the DC-3 planes. You need to make profitable routes for several of these. You want either New York or Washington as one of your early airports. Don't forget to keep buying landing rights, or the AI competitors will lock up some of the more desirable landing slots. After about 18 months, start saving money to get your first bigger plane, the DC-4 or DC-6. These fly many more passengers and have much longer range. Also make 5x the profits on a good longer route.