Spirit's top two markets are Fort Lauderdale, Fla., and Detroit. It is No. 1 in the former, holding 20% of the market, and No. 2 in the latter, holding about 5% of the market, which is dominated by Delta ( DAL). Atlantic City is a key market, as is Myrtle Beach, where Spirit is the only carrier to fly big jets as opposed to regional jets. In terms of the operational realities of the airline industry, the charge makes perfect sense because it addresses a major problem: delays incurred when passengers search for space in overhead bins, typically to stash their roller boards. By cutting five minutes from the time each aircraft spends at the gate, Spirit could gain 15 hours of flight time each day, Baldanza said. The carrier's 29 aircraft make about a half dozen "turns" each day. However, the airline industry is also sensitive to public and Congressional opinion. On Sunday, Sen. Charles Schumer (D-N.Y.) said five airlines told him that they will not institute fees for carry-on bags. These include Delta, American ( AMR), United ( UAUA), US Airways ( LCC) and JetBlue ( JBLU). Spirit doesn't care what other carriers do. "We're indifferent about whether they follow," Baldanza said. However, it is worth noting that Spirit was the first U.S. carrier to charge for the first checked bag, starting in June 2007. It was not until February 2008 that United became the first major carrier to follow. In the end, Baldanza is clearly pleased by the furor over Spirit's fees. He is, after all, a marketing guy who was previously senior vice president of marketing at US Airways, and free publicity is something he values. Asked whether he believes all publicity is good publicity, Baldanza said no, but: "Our sales are up and the media exposure is big and becoming more balanced, and that combination is a good one for Spirit." -- Written by Ted Reed in Charlotte, N.C. .