The Remain campaign leaflet says “the EU rules have reduced airfares”. EU rules have created greater competition between air lines but you can’t say what the aviation authorities might have achieved by now anyway. It is not correct to attribute all of these reductions to the EU. Some of the super cheap flights are due to subsidisation by travel companies and hoteliers who want you to fly. Also I have an impression that air travel has got much cheaper everywhere not just in/to/from the EU. I think implying this is a big thing we will lose if we leave seems a bit weak because we probably won’t.