O’Hare International Airport is on pace to again be the world’s busiest airport, a designation it lost a decade ago, Chicago city officials said Wednesday.

Hartsfield-Jackson Atlanta International Airport wrestled the top honor away from O'Hare in 2005 and has retained it since, according to the official flight count by the Federal Aviation Administration. O'Hare previously had bragging rights to the title since the dawn of the Jet Age, when it surpassed the number of flights at Midway Airport, which had been the leader.

From January to August of this year, 585,517 flights departed or landed at O’Hare, according to the FAA. However, Atlanta’s airport was not far behind, at 582,138, or 0.6 percent fewer. Atlanta edged out O’Hare by 3 percent in 2013.

City officials say part of the move is due to international passenger volume, which through the first half of the year rose 8 percent at O’Hare, to 5.2 million passengers. In the last 18 months, O’Hare and Midway airports together added six new international airlines and dozens of destinations, according to the city.

FAA data show the key to O’Hare’s move to pass Atlanta was losing fewer flights during the first eight months of the year. The number of total flights is down at both airports, down 0.85 percent at O’Hare and down 5.6 percent at Atlanta, according to FAA numbers.

O’Hare might be the busiest airport but during some months it’s also among the worst for flights departing on time, according to data from the U.S. Department of Transportation. However, the most recent numbers, for July, show O’Hare flights departed on time 73.6 percent of the time, trailing modestly the average of 75.3 percent.

Scott Gustin with Tribune Broadcasting talks on the phone with WGN Midday News. Scott Gustin with Tribune Broadcasting talks on the phone with WGN Midday News. SEE MORE VIDEOS

The announcement about O’Hare’s pace was made at the end of the 20th World Route Development Forum, being hosted in Chicago in recent days. The convention brings together airports and airlines as a networking event and helps shape the future of aviation routes.

gkarp@tribune.com