Just months after emerging from Chapter 11 bankruptcy, Spirit Airlines is warning about its future ability to stay in business. Spirit Aviation Holdings, the budget carrier’s parent company, says it has “substantial doubt” about its ability to continue as a going concern within the next year — which is accounting-speak for having the resources needed to sustain operations.

Spirit Airlines on Monday warned investors and passengers that it may no longer be in business in a year even after a successful bankruptcy restructuring and recent attempts to generate