(Adds updated Buttigieg statement, United statement)
By David Shepardson
WASHINGTON, Nov 28 (Reuters) - The U.S. Transportation Security Administration (TSA) said it screened 2.56 million air passengers on Sunday, the highest number since December 2019 and the busiest day since the start of the COVID-19 pandemic.
The number was, however, below the 2.88 million screened on the same day in 2019 at the end of the busy U.S. Thanksgiving travel period.
Between Nov. 18 and Sunday (Nov. 27), airlines carried 22.2 million U.S. passengers compared with 23.5 million in the same period in 2019, down by about 5.5%.
U.S. airlines reported very few cancellations over the holiday travel period, including 177 on Sunday and 56 on Monday, according to FlightAware.
U.S. Transportation Secretary Pete Buttigieg said Monday on Twitter that "the system did well. Sunday's weather led to an elevated but not extreme level of delays (5.3%) & overall cancellation rates held below 1.0%."
United Airlines said Sunday was its third-busiest travel day of 2022, with more than 476,000 customers traveling and it completed 99.8% of flights over the week.
U.S. airlines had planned to operate 13% fewer domestic flights during the eight-day Thanksgiving travel period compared with 2019, data by Cirium showed, but often with larger planes.
Airlines and Buttigieg clashed for months over summer problems that led to tens of thousands of flight disruptions and prompted the department to pressure airlines to do more to boost customer service to passengers.
In September, President Joe Biden said his administration had cracked down on U.S. airlines to improve treatment of passengers, a claim rejected by the carriers.
"My administration is also cracking down on the airlines to get passengers fairer treatment," Biden said. "Secretary Buttigieg, at my request, called them out." (Reporting by David Shepardson; Editing by Toby Chopra and Alexander Smith)