Twenty eight planes were stuck on the ground at US airports for more than three hours that month, the height of the summer travel season. Eighteen of those planes were operated by US carriers.

Sixteen of the US flights were going in or out of Chicago O’Hare International Airport on July 13, a day of severe thunderstorms. All of the longest delays were on regional carriers that operate smaller jets for larger airlines.

There was only one international flight that sat on the ground for more than four hours, and it’s susceptible to a big fine. Caribbean Airlines flight 526 from Georgetown, Guyana to New York’s JFK Airport sat on the ground for four hours and three minutes. US and international airlines can be fined up to US$27,500 per passenger if a flight is stuck for more than three hours.

The last time there were more three-hour delays in a single month was October 2011. There was just one long delay last July.

Overall, flights were less on-time in July than they were in both June 2012 and July 2011. United Airlines, which has a base in Chicago, had the worst on-time rate. US Airways had the best on-time rate for a network carrier, but Hawaiian Airlines and Alaska Airlines topped the overall list.

As more flights were stuck and passengers grew frustrated, they complained much more. The Department of Transportation received just under 2,500 complaints in July, almost double a year earlier and up 50 per cent from June.

They also had more reason to complain about lost or damaged bags. The mishandled baggage rate fell from a year earlier but was up from June.