Note that this very much only worked one way: Europe to the US, not vice-versa, because of the curvature of the Earth (and even then, better for London versus P

Note that this very much only worked one way: Europe to the US, not vice-versa, because of the curvature of the Earth (and even then, better for London versus Paris because of geography). Since the plane needs to be full on all of it's flights to pay it's costs, this was quite the problem and very much a limit on routes that could be profitable.