The report notes that flight cancellations during the last six months of 2021 were up 16 per cent compared to the last half of 2019, with cancellation rates increasing at seven of the 10 largest US airlines. Cancellation numbers remained high during the first four months of 2022, totalling nearly 82,000, up from 56,000 and 67,000, respectively, during those four months of 2018 and 2019. 

While high incidences of cancellations have been well documented, the GAO said the causes of cancellations at the end of 2021 shifted proportionately toward airline culpability. In 2018 and 2019, weather was the leading cause of cancellations. But the causes began to change in February 2021, when airlines found themselves unprepared for the sudden explosion in demand for flights.

During the second half of 2021, the 10 largest US airlines attributed a higher percentage of cancellations to causes within their control than in 2019. For some airlines, such as JetBlue, United and Allegiant, that percentage increased several-fold. 

In interviews with GAO investigators, airlines and other industry stakeholders cited previously discussed problems, such as shortages of pilots and other staff, as well as delays in training, for cancellation spikes. Increased employee reluctance to accept shifts was another reason cited by both airlines and their unions. One union said airlines over-scheduled flights. 

The airlines responded to the increase in controllable cancellations by increasing hiring, reducing flight schedules, increasing training capacity and implementing technological improvements, according to the report.

The GAO concludes that airlines have also been forced to make changes due to more aggressive action by the Department of Transportation. The report notes that as of March, the department was investigating four US airlines for possible unrealistic scheduling, including Southwest, which cancelled 16,700 flights between 21 and 31 December last year in the wake of a major winter storm.