Delta had about 3,900 flights scheduled for Sunday, meaning it canceled about 2.6% of its flights that day.
Delta said the majority of passengers whose flights were canceled were rebooked for the same day.
“We apologize to our customers for the inconvenience,” the airline said in an email. “As more of our workforce becomes vaccinated and more pilots return to active flying, we are confident in the reliability of our flight schedule heading into the spring and summer.”
Last year amid the sharp decline in travel due to the COVID-19 pandemic, Delta put 1,700 junior pilots on inactive status. They have had to go through training before flying again. Pilot retraining was an issue for Delta late last year, too, causing mass flight cancellations over the Thanksgiving and Christmas periods.
What’s more, the Federal Aviation Administration says that, after each dose of the COVID-19 vaccine, pilots cannot fly in the cockpit as crew for 48 hours, due to potential side effects.