Les autorités regardent l'origine des vols et savent que, si le vol vient de Montréal, il y aura des citoyens européens et d'autres citoyens, certains étant en transit, d'autres non, selon l'aéroport concerné.
They can look at a specific flight and know that if it's a flight from Montreal, then depending on the airport, it's probably going to have a mixture of EU and non-EU citizens, some in transit, some not.