The country's three main international airports at Dublin, Shannon and Cork serve many European and intercontinental routes with scheduled and chartered flights. The London to Dublin air route is the ninth busiest international air route in the world, and also the busiest international air route in Europe, with 14,500 flights between the two in 2017. In 2015, 4.5 million people took the route, at that time, the world's second-busiest. Aer Lingus is the flag carrier of Ireland, although Ryanair is the country's largest airline. Ryanair is Europe's largest low-cost carrier, the second largest in terms of passenger numbers, and the world's largest in terms of international passenger numbers.