Yep. Of course there are ton of solutions that seem better at a glance. More digits! Alphanumeric! Problem is decades and decades of software with the assumpti

Yep. Of course there are ton of solutions that seem better at a glance. More digits! Alphanumeric! Problem is decades and decades of software with the assumption of 4 digit flight numbers baked in. My hunch would be an additional airline code would probably be the easiest solution.