(Reuters) -United Airlines said on Thursday that it would expand its winter schedule and add flights to 15 cities including Fort Lauderdale, Orlando, and Las Vegas.

United's move aims to cash in on flights operated in key regions by Spirit Airlines, days after the no-frills pioneer filed for bankruptcy protection for the second time in a year.

"If Spirit suddenly goes out of business it will be incredibly disruptive, so we're adding these flights to give their customers other options if they want or need them," said Patrick Quayle, United's senior vice president of Global Network Planning and Alliances.

The new flights will begin in January, with tickets on sale later on Thursday.