Spirit Airlines shares soared by as much as 65% on Monday after the budget airline struck a deal to extend its debt refinancing plan by two months. The agreement with US Bank National Association to push the deadline — which was set to expire Monday — until Dec. 21 provides some wiggle room for Spirit to refinance its $1.1 billion loyalty bonds due to mature next year. The Florida-based airline said it has fully drawn down its $300 million revolving credit facility and expects to end the year with more than ...