Delta Air Lines says its cancellation of 4,000 flights over five days in the wake of a one-day thunderstorm in Atlanta will cause a $125 million hit to its profit.

CEO Ed Bastian made his first public remarks since the cancellations last week during the company’s quarterly financial update Wednesday.

“To our customers, we apologize for the disruption to their schedules,” Bastian said. He said the event provides “fertile ground for improvements for the future.”

In a memo to employees this week, Bastian wrote: “We let you down, and I want to let you know we are taking steps to restore your confidence.”

“Thousands of our customers have been inconvenienced and frustrated during this situation,” Bastian wrote in the memo reviewed by The Atlanta Journal-Constitution. “I have personally heard from many of them who feel like Delta let them down.”

Out of about 80,000 Delta employees, roughly 30,000 are based in Atlanta, including at the company’s headquarters, its call center and its massive hub at Hartsfield-Jackson International Airport.

“Your dedication to your jobs, our customers and each other was the shining light amid the storm and it is your hard work that kept a bad situation from becoming even worse,” Bastian wrote to employees. “I want to apologize to all of my Delta colleagues for putting you in this position.”

Bastian acknowledged that the company needs to invest in improvements to its crew scheduling and information systems, and added that the problem was not understaffing.

“There were seven different thunderstorm cells that happened at a rapid-fire basis starting from early morning to evening” last Wednesday, Bastian said during the company’s financial update. “We had the virtual shutdown of Atlanta for the better part of the entire day,” combined with busy spring break travel that left little room to rebook customers.

Channel 2's Jim Strickland reports.

He said it was an “impact that in my 20 years at the airline we’ve never seen.”

“We certainly take full responsibility for making this better in the future,”  Bastian said, including technology investments with improvements to crew tracking and communication.

“We had crews calling in from all across the system,” Bastian said. “We were literally running the airline hour-by hour” to get the system “pieced back together.”

IT systems “were working throughout,” according to Bastian.

“It wasn’t a question that the IT didn’t work. It actuallyworked and it worked as designed. It got overwhelmed,” Bastian said.

Bastian said the flight schedule had to “be put together on the fly at an unprecedented level of volume.”

Delta spokesman Ned Walker said the company’s chief operating officer Gil West would do “a complete deep dive throughout the organization to find out lessons learned from all the different divisions.”