After a year on top of the busiest U.S. airport pinnacle, O'Hare shows no signs of losing its status.
O'Hare International Airport handled 919,704 flights in 2019, a 1.8% climb from 2018.
However, Midway International Airport's numbers dipped, related partly to the grounding of Boeing's 737 Max airplane. In 2019, there were 232,084 flights at Midway compared to 243,322 in 2018, a 4.6% decline.
At O'Hare, "we're reaping benefits of new runways and gates, which are allowing airlines to boost service," DePaul University transportation professor Joseph Schwieterman said. "Getting these projects done wasn't easy, but they are paying dividends."
O'Hare hosted 903,747 flights in 2018, which was the first time it had surpassed 900,000 since 2007.
It also stayed ahead of rival Hartsfield-Jackson Atlanta International Airport, which held the crown from 2015 through 2017.
O'Hare connects passengers to small cities as well as top international destinations, Chicago Department of Aviation spokesman Matt McGrath pointed out.
O'Hare's No. 1 status "is also a vote of confidence from our airline partners, who are continuing to invest and grow in Chicago," McGrath said. That is happening as a result of shifting the airfield to a parallel runway system, which nears completion this year, and O'Hare 21, a revamping that includes a new global terminal, concourses and gates, he added.
Schwieterman said "the latest numbers show that both American and United Airlines remain committed to keeping O'Hare major global hubs. We shouldn't take that for granted -- no other airport has two mega-hubs operating side-by-side.
He added, "the most impressive aspect of O'Hare's dominance is that Atlanta hasn't been affected as much by the grounding of the 737 Max" as other airports. Delta's hub is at Hartsfield-Jackson, and the carrier "doesn't use the Max."
McGrath said the decrease in Midway flights is "very much connected to the grounding of the Max, and changes to Southwest Airlines' schedule that resulted."