There were eight planes stuck on the ground for more than three hours in September, the first month that international flights were included in the tally.
The government said Thursday that three of the extended delays were domestic flights. They were all trying to leave from Washington Dulles on Sept. 14, when severe thunderstorms were in the area.
Big U.S. airlines have been required to report tarmac delays of than three hours since April of last year. They face hefty fines of up to $27,500 per passenger for the delays, which on an average plane could cost them millions of dollars. There were 20 such delays in the year after the rule went into effect, compared with 693 the year before. Only one fine has been issued.
On Monday the Transportation Department levied a fine of $900,000 on American Eagle, a regional affiliate of American Airlines, for holding hundreds of passengers on board 15 planes for hours in Chicago earlier this year.
Despite more long delays in September, U.S. airlines cancelled slightly fewer flights than a year earlier. Cancellations were way down from August, when Hurricane Irene forced many major airports to close and led to thousands of scrapped flights.
Overall more flights were late than a year earlier. About 84 percent of flights were on-time, compared with 85 percent in September of 2010. There were more on-time flights than in August, when major US airlines had an on-time arrival rate of around 79 percent.
Airlines reported fewer problems with lost or damaged bags in September compared with both the month and year before. Complaints soared from the same month in 2010, rising 29 percent. They were down 31 percent from August, one of the busiest months for air travel. September is one of the lightest.