http://www.europarl.europa.eu/RegData/etudes/STUD/2017/602028/IPOL_STU(2017)602028_EN.pdf
https://committees.parliament.uk/publications/8781/documents/88926/default/
https://www.esri.ie/system/files/publications/QEC2019SPR_SA_Bergin.pdf
http://openeurope.org.uk/today/blog/will-brexit-ground-flights-europe/