United Airlines and Spirit Airlines are clashing over the future of ultra-low-cost carrier (ULCC) models.

While Spirit has thrived on this model, it filed for its second bankruptcy in under a year late last month.

Speaking at an industry conference on Thursday, United Airlines CEO Scott Kirby predicted Spirit Airlines would soon be out of business.

"That is a fundamentally broken business model, and the consumer has voted. They are going out of business because customers do not like their product," Kirby told moderator Brian Sumers, an airline industry journalist, according to APEX.

When asked how he was so confident in the prediction, Kirby said simply, "because I’m good at math."

The sentiment is similar to one that Kirby expressed at the U.S. Chamber of Commerce’s Global Aerospac

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