The United States has an extensive air transportation network. In 2013, there were 86 airports in the U.S. that annually handled over 1,000,000 passengers each and eight of the world's thirty busiest airports by passenger volume in 2020 were in the U.S. (down from 12 in 2014), including the world's second busiest, Hartsfield-Jackson Atlanta International Airport. In 2012, 88% of all traffic was through the 62 busiest airports in the country. In terms of cargo, in 2015, eight of the world's thirty busiest airports were in the U.S., including the world's second busiest, Memphis International Airport, behind only Hong Kong International Airport in China. Private aircraft are also used for medical emergencies, government agencies, large businesses, and individuals, see general aviation. Due to the geography of the United States and the generally large distances between major cities, air transportation is the preferred method of travel for trips over , such as for business travelers and long distance vacation travelers. For cities closer together in the Northeastern part of the country (e.g. Boston, New York City, Philadelphia, Baltimore, and Washington D.C.), the Northeast Corridor rail line carries the majority of intercity traffic. From the start of the Great Recession to the early 2010s, air traffic in the U.S. declined and the U.S. government reported 1.2 million fewer scheduled domestic flights in 2013 than in 2007. Air traffic volume also dropped sharply during the Covid-19 pandemic. At the same time, the airline industry has also experienced rapid consolidation with all of nation's largest carriers experiencing mergers. The average domestic airline fare steadily increased from 2009 until the first quarter of 2017 where it retreated to the same average of 2009, the lowest the average fare has been since 1995. History On January 1, 1914, pioneering aviator Tony Jannus captained the inaugural flight of the St. Petersburg-Tampa Airboat Line, the world's first commercial passenger airline. World War I When the U.S. entered the World War I in April 1917, it had already been lagging behind its European counterparts in aircraft production. This was largely due to the fact that the U.S. entered the war much later, when most of the European countries were already pressured to advance their aircraft technologies to outcompete one another. The Europeans had already developed standardized mass production of aircraft, while the U.S. was forced to expand to meet their wartime necessities. Even so, most of the aircraft used