Spirit Airlines said Monday that it has filed for bankruptcy protection and will attempt to reboot as it struggles to recover from the pandemic-caused swoon in travel and a failed attempt to sell the airline to JetBlue.

Spirit, the biggest U.S. budget airline, has lost more than $2.5 billion since the start of 2020 and faces looming debt payments totaling more than $1 billion over the next year.

Spirit said it expects to operate as normal as it works its way through a prearranged Chapter 11 bankruptcy process and that customers can continue to book and fly without interruption. All tickets, credits and loyalty points remain valid, the airline said, as are affiliated credit cards and other membership perks.

Shares of Spirit Airlines Inc., based in Miramar, Florida, dropped 25% on Friday, after The Wall Street Journal reported that the airline was discussing terms of a possible bankruptcy filing with its bondholders. It was just the latest in a series of blows that have sent the stock crashing down by 97% since late 2018 — when Spirit was still making money.

Shares rose nearly 4% before the opening bell Monday.

CEO Ted Christie confirmed in August that Spirit was talking to advisers of its bondholders about the upcoming debt maturities. He called the discussions a priority, and said the airline was trying to get the best deal it could as quickly as possible.

“The chatter in the market about Spirit is notable, but we are not distracted,” he told investors during an earnings call. “We are focused on refinancing our debt, improving our overall liquidity position, deploying our new reimagined product into the market, and growing our loyalty programs.”

People are still flying on Spirit Airlines. They’re just not paying as much.

In the first six months of this year, Spirit passengers flew 2% more than they did in the same period last year. However, they are paying 10% less per mile, and revenue per mile from fares is down nearly 20%, contributing to Spirit’s red ink.

It’s not a new trend. Spirit failed to return to profitability when the coronavirus pandemic eased and travel rebounded. There are several reasons behind the slump.

Spirit’s costs, especially for labor, have risen. The biggest U.S. airlines have snagged some of Spirit’s budget-conscious customers by offering their own brand of bare-bones tickets. And fares for U.S. leisure travel — Spirit’s core business — have sagged because of a glut of new flights.

The Association of Flight Attendants told union members early Monday that it does not expect any furloughs, or changes to pay or working conditions. The union also said that it has retained bankruptcy counsel.