@Walter Hinteler,
An interesting discussion is going today between the CEOs/spokespersons of various airlines here in Germany (Since I couldn't find a link in English, I just paragraph that).
Basically, the situation of flying between the UK and the EU-countries will be like 1973 from 2019 onward .... if no deal is made before. (Ryanair's Michael O'Leary* blamed France and Germany for doing that, but other airlines countered that they are affected as well.)
Travel companies make their deals at least 18 months in advance, in a couple of weeks, you can buy flight tickets for the period after March 2019 ... It is thought that air-traffic will be on the "divorce schedule" in 2018.
*Ryanair has a special interest because 40% of its flights to or from Ireland go to or come from the UK.