Advertisement Spirit Airlines has filed for Chapter 11 bankruptcy protection, it said Monday.The airline will continue to operate as normal, and all tickets remain valid, it added.Spirit has struggled since a proposed merger with JetBlue was blocked by a federal judge in March.Spirit Airlines has filed for Chapter 11 bankruptcy protection, it said Monday morning.In an open letter to customers, the budget airline said people can continue to book tickets and fly as normal as it undergoes a financial restruct ...