According to a first look at new data compiled by federal regulators, some regional carriers are retaining their flights better than industry giants such as American Airlines and Southwest Airlines.

A report from the US Department of Transportation released on Tuesday is the first to include details of regional carriers, a huge part of the airline industry that has been missing from departmental performance surveys for several decades. This year, more than half of domestic flights have been made by regional airlines or "code-share partners," as DOT calls it, carrying about a quarter of US air travelers.

In July, four major regional airlines – SkyWest Inc., Endeavor Air Inc., ExpressJet Holdings Inc. and Republic Airlines Inc. – posted better punctuality rates than US airlines United Continental Holdings Inc., Southwest and JetBlue Airways Corp.

SkyWest is ranked fourth in the industry with 80.4% of its flights at the time. SkyWest, the largest US-based regional airline in Utah, owns ExpressJet; Delta owns Endeavor. Mesa Air Group Inc., which operates for American and United, is also ranked among the top five airlines in the previous months.

The three largest US airlines, plus Alaska Air Group Inc. and Hawaiian Holdings Inc., use regional airlines to fill a large portion of their flight schedules.

In the new report, "the traveling public will see a more complete picture of the performance of regular passenger service," the department said in a press release. Regulators demanded that airlines start reporting in January, although they have not been released so far because they are under review, the department said.

The data suggests that US airlines have made concerted efforts in 2018 to enhance the reliability of their regional partners, who fly smaller 50- to 100-seat jets to route traffic to the hubs of major carriers.

Regional airlines still have higher cancellation rates than the major airlines. This is because smaller planes are cleaned before bigger ones in cases where airlines have to restrict their flights due to bad weather or congestion at the airport.

Delays continue to weigh on JetBlue Airways Corp., with only 69.1% of its flights in 2018, placing New York-based JetBlue behind its competitors, including two very low cost carriers, Allegiant Travel Co. and Frontier Airlines. JetBlue representatives did not respond to requests for comments via email.

American, the world's largest carrier, lagged 77.2 percent on the overall performance of its Delta Air Lines Inc. and United network. This compared to 82.5% for Delta and 78.4% for United. Delta regional carriers also flew more of their flights on time than the American and United regional carriers.

Hawaiian Airlines was at the top of the year rankings until July, followed by Alaska, which largely completed the integration of Virgin America. Delta was third.

Delayed aircraft were the main cause of delays (8.4%), followed by congestion problems in the national aviation system (6.7%), according to the DOT. Airlines delays accounted for 6% of late flights.

The industry has also continued to reduce the number of passengers who boarding is denied because of overbooked flights or other operational issues. The practice caught the eye last year after a man was fired from a United Express flight when he refused to voluntarily leave the plane.