Chief Executive Officer of Irish airline Ryanair Michael O'Leary attends a press conference at a hotel in London on August 31, 2016. Brexit will halve Ryanair's UK growth, Europe's largest airline said Wednesday, as it urged Britain to prove it was open for business post-Brexit by building new London runways. / AFP PHOTO / DANIEL LEAL-OLIVASDANIEL LEAL-OLIVAS/AFP/Getty Images