This summer travel season has been plagued by flight cancellations and delays as airlines deal with staff shortages, inclement weather and air traffic control delays. As of Saturday night, at least 636 flights to, into or out of the United States were canceled and an additional 5,921 domestic flights were delayed, according to FlightAware. Newark Liberty International and Chicago Midway International Airport topped the list of US airports with the most canceled flights, the flight tracking website said. American Airlines canceled 4 percent and delayed 24 percent of its Saturday flights, according to the website. Meanwhile, United had 4% of its flights canceled and 23% delayed, and Delta had 2% canceled and 22% of its flights delayed, FlightAware reported. About 41 percent of JetBlue flights and 36 percent of Southwest flights were also delayed Saturday, according to the website. “We continue to work on a variety of weather-related challenges across the country this weekend,” Southwest Airlines told CNN in a statement Saturday. “Our teams are working to get our customers to their destinations safely and as quickly as possible.” CNN reached out to the other domestic carriers for comment on Saturday’s delays and cancellations. Amid a flurry of flight cancellations and a flood of complaints from passengers, the US Department of Transportation proposed Wednesday to expand the circumstances under which airline passengers can receive refunds. The department said it has been inundated with complaints from airline passengers seeking refunds since the start of the Covid-19 pandemic. The proposed refund rules come after Pete Buttigieg held a private meeting with airline CEOs in June in which he told them to fix summer flight schedules that have been plagued by thousands of cancellations.