Spirit Airlines filed for bankruptcy protection Monday after the company struggled with a long run of quarterly losses, failed mergers and looming debt, but it plans to keep flying. Spirit's troubles deepened after the collapse of its $3.

Spirit Airlines tells customers that its bankruptcy will not impact their travel plans. Find out why it pays to use a credit card when booking your vacation.

The airline listed its estimated assets and liabilities in the range of $1 billion to $10 billion each, according to a court filing on Monday.