A Spirit Airlines Airbus A321 airplane taxis at Los Angeles International Airport after arriving from Fort Lauderdale on March 30, 2025 in Los Angeles, California. Kevin Carter | Getty Images Just hours after Spirit Airlines collapsed , its rivals unveiled their new flight plans. Airlines had actually been at work for months on their route changes as Spirit's shutdown looked more and more likely. Some new flights start this week. It comes after Spirit abruptly ceased operations overnight Saturday, stranding thousands of customers. The quick move shows how carriers are vying for Spirit's valuable assets, like airport gates and a customer base that has one less choice when booking. That could drive up airfare even more than it already has risen after the fuel-driven hikes this year, analysts said. Even though Spirit's already pared-down summer schedule was about 1.5% of U.S.…