Spirit Airlines is in talks with alternative investment firm Castlelake for a potential takeover as the discount airline looks for a path out of bankruptcy, CNBC has learned.

Spirit filed for Chapter 11 bankruptcy protection last August for the second time in a year after its previous turnaround plan fell flat.

Fellow budget carrier Frontier Airlines had been in talks with Spirit over the years for a potential merger, including in recent months, but didn’t secure a deal, according to people familiar with the matter, who requested anonymity to speak about the discussions. The two had reached a deal four years ago but it was called off after a surprise all-cash offer from JetBlue Airways.

“We don’t comment on market rumors and speculation,” a Spirit spokesman said. Castlelake didn’t immediately respond to requests for comment.

It was not immediately clear if Spirit’s bondholders and Castlelake would reach a deal or what form it could take. Minneapolis-based Castlelake has been active for years in aviation finance. In August, it announced it was launching a new aviation lending arm, Merit AirFinance, with $1.8 billion in deployable capital.

Spirit in mid-December said it amended its agreement with creditors to receive another $50 million in funding immediately, a lifeline for the carrier. Additional funding would be contingent on “further progress on a standalone plan of reorganization or a strategic transaction,” Spirit said Dec. 15. “Spirit is currently in active negotiations on each of these possibilities,” the company added.

In its fight for survival, Spirit has slashed flights, reduced its fleet and cut jobs to save money. Unions last year agreed to pay cuts for the carrier’s pilots and flight attendants. That amounted to $100 million in concessions, the Air Line Pilots Association said in a Jan. 13 open letter, urging bondholders to support Spirit’s restructuring and avoid a liquidation.

Dania Beach, Florida-based Spirit for years enjoyed largely steady profitability and enviable margins in the often-rocky airline industry. But things took a turn after the pandemic, when wages and other costs soared, customer preferences changed, and an oversupply of domestic flights drove down airfare. That was especially punishing for U.S.-focused carriers that don’t enjoy a buffer from plush first-class cabins and large credit card and loyalty program deals.

The carrier’s problems snowballed after a Pratt & Whitney engine recall grounded dozens of its Airbus aircraft starting in 2023 and the planned acquisition by JetBlue was blocked two years ago by a federal judge who ruled it was anticompetitive, leaving both carriers to fend for themselves against a backdrop where larger carriers dominate.

Spirit has been trying in recent years to win over higher-spending customers by offering roomier seats or bundled fares that include seat assignments and baggage, or allow for changes, to better compete with larger rivals whose profits have been buoyed by big-spending customers post-pandemic.