Airlines were running on time more often in June than they did last summer and travelers seemed to be finding less to complain about.

But that was before computer outages this month at Delta and last month at Southwest led to more than 4,000 flight cancelations, widespread delays and travel nightmares.

The Transportation Department said Wednesday that 78 percent of flights on major U.S. airlines arrived on time in June, up from 74.8 percent in June 2015.

The on-time rate slipped from May's 83.4 percent mark, however.

Hawaiian Airlines and Alaska Airlines had the best on-time ratings. American Airlines had the worst.

At least one in every four flights was late on American, Virgin America, Spirit Airlines, Southwest Airlines and JetBlue Airways. Flights that arrive at least 15 minutes behind schedule are considered late.

About 1 percent of domestic flights were canceled in June, down from 1.8 percent a year earlier but double May's 0.5 percent rate. Regional airline ExpressJet and Spirit were most likely to cancel a flight.

Delta Air Lines had the lowest cancellation rate in June, a record that was marred this month by a massive computer outage.

Travelers filed 1,078 complaints with the government about all U.S. airlines in June, down 31 percent from 1,567 a year earlier.

Southwest had the lowest complaint rate, while Spirit had the highest. Spirit passengers lodged complaints at least twice as often as travelers on any other airline and 13 times more often than Southwest customers.

For the first six months of 2016, complaints to the Transportation Department were down 12.2 percent from 2015. However, those figures don't include complaints that consumers lodge directly with the airlines - the airlines are not required to report those numbers.