The department stated that the cancellations and delays are "unacceptable," and it will be looking into whether they were within the control of the airline and whether Southwest is complying with its customer service plan and other relevant USDOT rules.
Southwest Airlines canceled 70% of its scheduled flights on Monday and has already canceled 60% of its planned Tuesday flights, according to FlightAware. The airline has also delayed a significant portion of its flights on Sunday and Monday. Southwest Airlines has issued an apology and stated that it is working to address the widespread disruption caused by the extreme winter weather.
Comparison of Southwest Airlines' Cancellation and Delay Rates to Other Major US Airlines
While other major US airlines have also experienced significant cancellations and delays in recent days due to extreme winter weather, the rates at Southwest Airlines have been significantly higher. On Monday, the airline canceled 70% of its scheduled flights and has already canceled 60% of its planned Tuesday flights. In comparison, the cancellation rates at other major US airlines have not been nearly as high, and they have largely recovered from the weather-related disruptions.

The USDOT has pointed to Southwest Airlines' customer service plan, which states that the airline will provide meal or hotel vouchers for extended delays that are due to issues within the airline's control but not for unforeseen issues such as weather. In August, several major US airlines, including Southwest, committed to providing meals for customers delayed by three hours and hotel rooms for stranded passengers in the event of delays caused by issues under the airlines' control.