KEY TAKEAWAYS Spirit Airlines shares are tumbling 40% in premarket trading Friday as the carrier reportedly is exploring a bankruptcy filing in the wake of its failed $3.8 billion merger with rival JetBlue Airways. According to The Wall Street Journal, the budget airline has been in talks with its bondholders over the terms of a chapter 11 filing. It also has been looking into restructuring its balance sheet as it grapples with billions of dollars of debt, the report said. Spirit Airlines (SAVE) shares are ...