CHICAGO (CBS) — United Airlines ranks dead last in a U.S. Department of Transportation analysis of on-time performance for the month of July, according to a published report.

As CBS 2’s Kris Habermehl reports, the Chicago-based airline was only on time with its flights 64.1 percent o f the time in July, the Chicago Tribune reported.

Normally, airlines are on time at least 77 percent of the time, and no other airline really went below that mark except United, the Tribune reported.

The Tribune says the airline experienced some issues with its reservations computer system, which has been causing problems since March.

The reasons United usually gave for the delays include late-arriving aircraft and air carrier delays. Weather was not a major cause for delays, the Tribune reported.

United flights from O’Hare International Airport to Baltimore-Washington International, Ronald Reagan Washington National, and Orlando International airports, the Tribune reported.

United was also the subject of the most complaints in July, with 995 formal complaints, or about half of all those lodged against airlines, the Tribune reported.

Last month, a three-hour meltdown of the worldwide reservations computer system created chaos for passengers. Customer service representatives had to write tickets by hand, as lines at Terminal 1 at O’Hare grew as bad as any O’Hare on Thanksgiving Eve.

United had struggled with reservations computer problems on and off since March, when it combined its reservations systems with those it inherited in its merger with Continental Airlines.

But the airline emphasizes that things are changing. A representative tells the Tribune that so far, on-air performance for September has been 80 percent.