The FAA differentiates primary and non-primary airports by the number of enplanements. A non-primary airport is an aerodrome with less than 10,000 passengers boarding each year. A primary airport is an aerodrome for passenger services with over 10,000 enplanements annually. A primary airport can be further broken down into four categories based on the share of overall passenger boardings: non hubs account for under 0.05 percent of the overall enplanements; small hubs - between 0.05 and 0.25 percent; medium hubs - between 0.25 and one percent; and large hubs account for over one percent of the total U.S. enplanements. Delaware is the only U.S. state without a primary airport.
The United States is home to some of the world’s busiest and most punctual airports. Atlanta’s Hartfield-Jackson International Airport handled over 104 million passengers in 2016, making it the world’s busiest airport . It was also the leading airport in terms of airport operations.
Chicago O’Hare International had the second largest number of airport operations. With total operating revenue of over 845 million U.S. dollars, the airport is United’s main operating hub, handling some 9.7 million passengers from United’s flights in 2016.
Los Angeles International Airport, colloquially know as LAX, was ranked fourth for airport operations. With around 300,000 flights arriving and departing, the airport handled over 56 million domestic passengers and some 21 million passengers on international flights in the fiscal year of 2016.