As a fix, it was made so that C/F pax are very sensitive to Route Image. So you can't do that right from the start. As far as I know, you can still do this later one in the game if you wanted once you have a high RI, but I've never tried it to see.
Oh! So you can still do magic carpets after building up route image on a normal plane?
So I can fly an all C/F Concorde and..break even?
Not possible either. You need to have at least as many Y seats as you have C/F, in order to sell any of the C/F-seats. I've been experimenting with this shortly after the magic carpets were 'forbidden'/made impossible. Having a CI of 90, and a RI of 100, I still needed 50% Y seats, in order to get C and F sold. Whereas you also need more C than F seats, because F seats are also sensitive of C-class.
Apparently this kindof destroys the margins of the CONC... having yet been the only player to operate them at a profit ever, it only worked from LHR with a seating of only C/F class. (not mentioning the details, as this is still a company secret
). Since these configs are made impossible, which does not mean technically impossible, you can still config your plane that way, but LFs end up between 0 and 10%, it has only hardly been possible to turn in profits on owned CONCs, not even talking about leased ones
I am still good with the change made, as it tended to be abused a lot in prior games, where it was still possible. With all C/F seats a LHR based airline in a DotM game could pull in 1-1.5M/week on a 707-320B just flying to JFK and coming back. This lead to rapid expansions of such airlines, which then a lot later would start carrying eco passengers, and would already be ruling the airport from early off, making it impossible to start up against them.