Spirit Airlines filed for bankruptcy protection Monday after the company struggled with a long run of quarterly losses, failed mergers and looming debt, but it plans to keep flying. Spirit's troubles deepened after the collapse of its $3.

The announcement comes before the busiest travel weekend, Thanksgiving, but the airline assured its customers that the tickets they booked are still active and future fares will also be.

The low-fare carrier has struggled to find its footing after its planned merger with JetBlue was blocked by a federal judge.