U.S. no-frills carrier Frontier Airlines is focusing on growing its network in "high fare" markets like Seattle and Detroit at the expense of its footprint in leisure markets such as Las Vegas and Florida in a bid to lift earnings, its CEO told Reuters. Frontier's struggles, along with some other discount carriers, has some analysts raising questions about their business model. Frontier CEO Barry Biffle pinned the blame on excess industry capacity in key leisure markets that has depressed airfares.