WASHINGTON — A top executive for Southwest Airlines is expected to tell Congress “we messed up” in a hearing Thursday that will explore the mass flight cancellations that left thousands of customers stranded for days over the holidays.

“Let me be clear: we messed up. In hindsight, we did not have enough winter operational resilience,” Southwest Chief Operating Office Andrew Watterson will say, according to prepared remarks obtained by NBC News ahead of the hearing of the Senate’s Commerce, Science and Transportation Committee.

The hearing is scheduled to begin around 10:30 a.m. ET.

Southwest has been under intense scrutiny after it canceled thousands of flights in December, leaving many passengers scrambling during the hectic holiday travel season. While other airlines had to disrupt services due to winter conditions, none were impacted like Southwest.

The Transportation Department said in January that it opened an investigation into the meltdown to look into “whether Southwest executives engaged in unrealistic scheduling of flights which under federal law is considered an unfair and deceptive practice.”

“The American people have a lot of questions about the Southwest debacle in December that left passengers stranded or unable to be with loved ones over the holidays,” said Commerce committee chair Sen. Maria Cantwell, D-Wash. in a statement released before the hearing. “We’re going to ask for answers to those questions. I’m interested in hearing the pilot’s testimony that this debacle could have been avoided if Southwest had made investments sooner.”

Captain Casey A. Murray, the president of the Southwest Airlines Pilots Association, is set to testify at Thursday’s hearing, along with Watterson; Paul Hudson, the president of the travelers’ rights’ group Flyers Rights; Sharon Pinkerton, an executive at Airlines for America, the trade group that represents airlines. Dr. Clifford Wilson, a senior fellow at the Brookings Institute, is also expected to testify remotely.

Cantwell also held a panel on Wednesday with constituents affected by Southwest’s issues.