According to CAPA and OAG, American Airlines was the world's busiest airline for the week beginning March 29, 2021.

American Airlines leads the ranking for domestic and international flights; more than three-quarters of its international flights are to Latin America and the Caribbean.

U.S. airlines have returned to the top positions in recent weeks as the U.S. domestic market has opened up, with more than one million daily passengers flying most days.

Each of the three largest U.S. carriers, American Airlines, Delta Air Lines, and Southwest Airlines, offer more than 3 million seats for the week, most of them in the domestic market. All of the major airlines have significant domestic routes, as international routes continue to languish.

The four biggest US airlines - American Airlines, Delta Air Lines, Southwest Airlines, and United Airlines - between them accounted for just over 20% of all seats flown across the world.

American again heads the world in terms of international seat numbers, but the profile of airlines in the top ranks changes considerably when only international seats are accounted for.

American's international seat numbers focus on short/medium-haul routes to the south.  Most of American Airlines' international seats are to holiday destinations in Latin America and the Caribbean, as US holidaymakers are limited in their international travel options.

As American ramps up its North Atlantic frequencies, the impact of these longer-haul routes can quickly be seen when the shares are shown in ASKs (or ASMs), with a much larger proportion of seat kilometers flown (22.5%), compared with seats flown (8.9%) in the previous graph.

Source: CAPA/OAG & AA