Federal regulators launched an investigation Tuesday as Delta Air Lines' woes following a technology glitch stretched into a fifth day, with nearly 1,800 more flights canceled or delayed and customers increasingly frustrated in trying to figure out how to get to their destinations.

U.S. regulators are looking into how the airline is treating passengers affected by canceled and delayed flights as it struggles to recover from a global technology outage.

Transportation Secretary Pete Buttigieg announced the Delta investigation. "All airline passengers have the right to be treated fairly, and I will make sure that right is upheld," he said.

Delta canceled 483 flights nationwide Tuesday by 8:30 p.m., according to tracking platform FlightAware.

The outage began last Thursday night into Friday morning, after a faulty software upgrade from cybersecurity company CrowdStrike derailed more than 8 million Microsoft computers worldwide.

The Atlanta-based carrier with a major hub at Minneapolis-St. Paul International Airport has canceled more than 6,600 flights since the outage started, far more than any other airline, according to figures from FlightAware and travel-data provider Cirium. The meltdown has crippled the airline, and the fallout has spread to hotels and rental car companies.

Delta said it was cooperating with the investigation.

Investigators are likely to focus on whether Delta is complying with federal rules and offering prompt refunds to passengers whose flights are canceled or significantly delayed. In a text provided to the Associated Press, a Delta passenger whose flight was canceled Saturday was told, "If you prefer not to rebook your trip, your ticket value will automatically be available as an eCredit that can be used towards a future Delta ticket."

Nightmares for thousands of stranded passengers continued Tuesday.

Scott and Connie Powers gave up trying to fly back home to Orlando after spending eight hours Monday at MSP hoping their Delta flight would take off. About 11 p.m., the couple, who had been in town for a wedding, learned their flight was a casualty of the ongoing meltdown.

"Who would have thought Monday would be worse than Friday?" Scott Powers said.

Powers thought he had secured lodging when he called and booked a room at the Quality Inn/Mall of America for $175 for the night — $50 more than advertised online. But the couple arrived to find the hotel was oversold. With the help of a police officer who was on site to remove another disgruntled customer, Powers was directed to another hotel well after 1 a.m.

On Tuesday, lines were just as daunting at the Enterprise counter in Brooklyn Center, where Powers showed up to pay $400 to rent a car to drive to Florida to find lines as long as those in the airport terminal and people sitting on sidewalks waiting for availability.

Other hotels near the airport saw travelers filling any unused rooms as they waited to get new Delta flights.

Mary Wadlow has been in Cooperstown, N.Y., to watch Twins legend Joe Mauer get inducted into the National Baseball Hall of Fame over the weekend. She made it back to the Twin Cities at midnight Monday, but only because she used all the tools at her disposal. She checked flightaware.com to find when flights were leaving Syracuse, N.Y., went to the airport, worked with the airport manager at the ticket counter and got booked on flight to Minneapolis via Detroit.

"Delta never offered that," Wadlow said. "It's all about knowing how to use FlightAware, knowing where other flights are and what their status is. It's all about advocating and being savvy. I can't imagine the Delta meltdown and not being an experienced traveler."

Given the magnitude of the meltdown, things at Delta may not get better for days, said Kyle Potter, editor of Thrifty Travel.

"It broke Delta's operations … pushed them past the breaking point," he said in a phone call.

While other airlines that were hit have largely recovered, Delta continues to struggle to get flights back in the air. The more than 4,000 flights canceled through Sunday and 1,150 on Monday, according to FlightAware, is more than in 2018 and 2019 combined, Potter said.

With so many planes and crews now out of position, and the system used to schedule them still languishing, it's questionable whether Delta will be a reliable airline by the weekend, Potter said.

"If you need to be somewhere, it's time to book a flight with another airline," Potter said. "I always say hope for the best and plan for the worst, and right now I have no hope a Delta flight will take off with any certainty, or at all."

The collapse at Delta is stunning given that it was widely viewed as the best big U.S. airline — the most profitable before and after the pandemic, and the best-run. Delta has almost always ranked near the top among U.S. carriers for on-time performance.

Thousands of passengers with few options remained stranded Tuesday at Delta hubs, including Salt Lake City, Detroit, Boston, Minneapolis and New York. Alan Oberg of Sioux Falls has been stuck in Atlanta for the past four days, unable to get to North Carolina for a vacation or get back to South Dakota.

"It's a cluster," he said in a phone interview. "We have been bumped four times and put on standby. The app does not work, the internet barely works."

Oberg and his wife, Jen, were able to go the local aquarium, but they have spent many hours in the airport hoping and praying to get on a flight. He said he might get out of Atlanta on Wednesday.

Overnight Monday into Tuesday, lines formed at MSP with travelers standing in the concourses waiting well after midnight to rebook flights.

Delta said it's working hard to clear the backlog.

"I want to apologize to every one of you who have been impacted by these events," the airline's CEO Ed Bastian wrote to passengers in an email. "Delta is in the business of connecting the world, and we understand how difficult it can be when your travels are disrupted. Canceling a flight is always a last resort, and something we don't take lightly."

Delta has offered waivers to passengers with trips planned through Tuesday, allowing them to rebook trips and have fare differences waived through Sunday. Travelers who had a "significant" delay or cancellation can also request a refund, according to Delta's cancellation and delayed flight information web page.

Potter reminded travelers to be as patient and kind as possible when interacting with gate agents, customer service representatives and those behind the ticket counter. "It's not their fault," he said.

This story contains material from the Associated Press.