The CEOs of United and Frontier airlines are creating turbulence of their own just ahead of the holiday travel season.

Barry Biffle, the CEO of low-cost carrier Frontier, shot back at his United counterpart Wednesday for his comments predicting the end of Spirit Airlines and the budget flight industry as a whole.

“That’s cute,” Biffle said Wednesday at the travel-centric Skift Global Forum, CNBC reported.“If he’s good at math, he would understand that we have a [flight] oversupply issue in the United States.”

Biffle came to Spirit’s defense after United CEO Scott Kirby said the low-cost airline, which declared bankruptcy for the second time this year, was going to go out of business. When asked at a conference last week why he was so sure, Kirby replied, “Because I’m good at math.”

Biffle’s ambition to have Frontier surpass Spirit as the top ultra-low cost carrier would make him the “last man on a sinking ship,” Kirby added.