(NewsNation) — Southwest Airlines is expected to apologize before a U.S. Senate committee over the holiday meltdown that led to the cancellation of 16,700 flights and pledge changes to ensure that there will be no repeats.

Chief Operating Officer Andrew Watterson is expected to apologize before the Senate Commerce Committee for the airline’s crew scheduling system, which it said was overwhelmed by the volume of changes, along with pledging that the company will budget more than $1 million for IT upgrades.

“Let me be clear: we messed up. In hindsight, we did not have enough winter operational resilience,” according to Watterson’s written testimony obtained by NewsNation.

Thursday’s hearing, titled “Strengthening Airline Operations and Consumer Protections” will also include Southwest Airlines Pilots Association President Captain Casey Murray, Sharon Pinkerton, a senior official with Airlines for America, an industry group, and Paul Hudson, who heads Flyers’ Rights, a passenger advocacy organization.

In written testimony seen by Reuters, Southwest Airlines Pilots Association (SWAPA) President Casey Murray is expected to tell the committee that the low-cost carrier’s “overconfidence” in planning and a “systemic failure to provide modern tools” were responsible for the December meltdown that the union said stranded 2 million passengers and is estimated to have cost it more than $1 billion.

Murray is expected to tell the committee that pilots “have been sounding the alarm about (Southwest’s) inadequate crew scheduling technology and outdated operational processes for years. Unfortunately, those warnings were summarily ignored.”

He blames the meltdown on “poor planning, systemic under-investment in crew scheduling technology and processes and a failure to collaborate with frontline employees.”

Murray said Southwest’s mismanagement forced the airline during the crisis to fly more than 500 flights without passengers to reposition crew or planes and more than 10,000 flights where pilots sat in the back rather than flying.

He said Congress should demand “a firm timeline for when crew scheduling technology and associated crew management processes will be fixed.”

Meanwhile, more than six weeks have passed since the holiday travel nightmare, but it feels fresh for Lauren Smith.

“I think I was at the airport for a total of 27 and a half hours,” she recalled.

Smith’s luggage was lost for eight days.

“I got a phone call at two in the morning saying your bags are here do you want to come get it,” Smith recalled.

The holiday meltdown will cost the company between $725 million and $825 million, the airline said in a regulatory filing on Jan. 6.

“When you are running your operation as hot as Southwest is running it with an infrastructure and IT infrasture that is compromised and isn’t up to the standards of many today and computer systems from one department doesn’t speak to another department, yes, it concerns me it with fatigue for crews for pilots,” said Lyn Montgomery with the Southwest Flight Attendants Union.

“I think you are going to have to see some serious investment in technology from Southwest to make sure this doesn’t happen again because it was a huge black eye for Southwest,” said Clint Henderson, with The Points Guy.

Southwest promised its customers impacted by the surge of flight cancellations 5,000 frequent-flyer points and reimbursement for travel expenses.

Smith said she received her full $1,300 back instantly, but it still doesn’t feel right.

“I think I want to hear a genuine apology The first one felt scripted to me because they got caught,” she said.

Smith said her loyalty is dashed, and the airline is her last resort now.

Reuters contributed to this story.