In the land of the free, the airline/aircraft owners would just prohibit firearms themselves, and implement security the same as, or possibly more stringent that what the feds do. They would at least be more effective at it, since they would have something to lose if they failed, namely their jobs or profit. Unlike federal employees, which are practically impossible to fire.
Of course there could be an airline that would advertise itself as carry friendly, but they would probably lose more business due to fear or the general public, than they would gain from armed citizens.
You can also always carry on your own private airplane, or one of a friend, it's completely legal.
I should point out, that LEOs only have to take a one day powerpoint presentation known as the armed while flying course, to carry weapons on board commercial passenger aircraft. This includes local LEO as well. As if their marksmanship training wasn't a joke to being with. But to be fair, the reason most LEOs, federal, state, or local, generally are armed while flying isn't to prevent issues on board, but because they need to be armed immediately at their destination, or are possibly transporting a prisoner.
