Spirit Airlines is set to announce in the coming hours that it will halt flying as of 3 am ET Saturday, according to two sources familiar with its plans, making it the first significant US airline to halt operations in nearly 25 years. The shutdown comes as soaring jet fuel prices derailed its plans to emerge from its second bankruptcy. Efforts to reach a deal with the Trump administration on an 11th-hour rescue package that was also acceptable to a key group of creditors proved unsuccessful Friday.