Spirit Airlines filed for bankruptcy as its ultralow discount model proved insufficient to satisfy its hefty debt obligations after its merger with JetBlue Airways was blocked. Spirit filed a chapter 11 petition in the U.S. Bankruptcy Court for the Southern District of New York seeking to restructure its debts to bondholders and survive more intense competition from larger airlines for value-minded fliers. The Wall Street Journal reported earlier this month that Spirit was preparing to file for bankruptcy.