Using Hexadecimal instead gives over 6.5 times as many possibilities in the same 4 characters - should be more than adequate. I know airline systems have a lot

Using Hexadecimal instead gives over 6.5 times as many possibilities in the same 4 characters - should be more than adequate. I know airline systems have a lot of legacy code so it might be difficult, but at least logistically (having adequate space to print / display them), and for humans to deal with it's not too difficult.