Traveling can be a headache and, at worst, a nightmare.

And while many airlines often blame flight delays and cancellations on factors beyond their control, namely the weather, a new report shows that may not be the case.

Researchers at the U.S. Government Accountability Office (GAO) studied flight cancellations from January 2018 through April 2022 and found that most were caused by factors beyond the airline’s control — largely a lack of adequate crew and aircraft maintenance issues.

The study found that more flights were canceled in the second half of 2021 than in 2018 and 2019 combined, even though 14% fewer flights were scheduled during that period. The number of cancellations continued to rise until the end of April 2022.

The data shows that the leading cause of cancellations from October to December 2021 was aircraft maintenance and lack of crew. Delays in the last half of 2021 were also largely caused by airline-controlled factors.

“Stakeholders said operational challenges, including the need for additional pilots and crew, have made it more difficult for airlines to manage flight disruptions,” the study said. “In response, airlines have added new staff, opened new training facilities and reduced the number of scheduled flights, among other things.”

The GAO said the investigation was conducted to examine the core reasoning behind the frequent flight delays and cancellations due to the pandemic at a time when the airline industry was starting to boom again.

Airlines were bombarded with cancellations and delays in late 2022 and the first half of 2023.

Last December, Southwest Airlines infamously made headlines when it canceled hundreds of flights just before and before Christmas, leaving thousands stranded and without their luggage.

A recent study by WalletHub ranked it as the worst airline of 2023. Delta Airlines was named the best.