Southwest Airlines is the world's fourth-largest carrier by September flights. Examining its entire network using Cirium Diio data shows that it has 3,733 daily services (given its former use of the 737-300, I like that number). It is surpassed by American Airlines (5,867), Delta Air Lines (4,960), and United Airlines (4,793).

While the evolving carrier ranks fourth overall, its all-Boeing 737 fleet (and no use of regional jets) means that it is the US's second-largest domestic operator by seats for sale. Some 17.8 million are available in September, which is second only to American (18.5 million).

Southwest's Top 10 Routes By September Flights

Southwest is undergoing many well-discussed changes to its product, operations, and network. The latter includes even more very sho

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