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 failed attempts to sell itself to JetBlue and Frontier Airlines.

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, obligations that it’s unlikely to be able to meet.

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.

Shares of Miramar, Florida-based Spirit 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.

In October, Spirit and Frontier revived merger talks after discussions in 2022 ended with JetBlue outbidding Frontier, according to the WSJ. A federal judge blocked the JetBlue merger in January over antitrust concerns.