The world's largest airlines can be defined in several ways. American Airlines Group is the largest by its fleet size, revenue, profit, passengers carried and revenue passenger mile. Delta Air Lines is the largest by assets value and market capitalization. Lufthansa Group is the largest by number of employees, FedEx Express by freight tonne-kilometers, Ryanair by number of international passengers carried and Turkish Airlines by number of countries served.Groups such as the International Civil Aviation Organization
establish worldwide standards for safety and other vital concerns. Most
international air traffic is regulated by bilateral agreements between
countries, which designate specific carriers to operate on specific
routes. The model of such an agreement was the Bermuda Agreement
between the US and UK following World War II, which designated airports
to be used for transatlantic flights and gave each government the
authority to nominate carriers to operate routes.
Bilateral agreements are based on the "freedoms of the air",
a group of generalized traffic rights ranging from the freedom to
overfly a country to the freedom to provide domestic flights within a
country (a very rarely granted right known as cabotage).
Most agreements permit airlines to fly from their home country to
designated airports in the other country: some also extend the freedom
to provide continuing service to a third country, or to another
destination in the other country while carrying passengers from
In the 1990s, "open skies"
agreements became more common. These agreements take many of these
regulatory powers from state governments and open up international
routes to further competition. Open skies agreements have met some
criticism, particularly within the European Union, whose airlines would
be at a comparative disadvantage with the United States' because of cabotage restrictions.