There's also a fairly good argument for this in the line of trains and highways. Planes aren't physically trapped on one course, but pretty much every nation heavily regulates who can fly where, when. Airports are often state-controlled, and even private ones need state approval to add new runways or flights.

What we have now is one of the ridiculous "private non-market" arrangements. When airlines in Europe fly empty planes to stop the government from taking their flight slots away, that's not the fault of the companies, but it's also not a functional market we should expect efficiencies from.

I'm not a fan of "regulate markets into dysfunction then nationalize them", but if the fundamental restraints on travel are too severe to let the market function freely, privatization stops making much sense.