"Older airplanes have more mechanical issues than newer ones. But does that make them unsafe? Absolutely not."

For the last decade, Allegiant Air has built a thriving business buying secondhand jets and connecting small cities to leisure destinations like Las Vegas and Honolulu.

By keeping costs low, offering cheap fares, and flying from places that other carriers have neglected, like Fort Wayne, Ind., or Allentown, Pa., Allegiant has grown rapidly. Today, the airline has one of the highest profit margins in the business and among the lowest costs.

It has also become the dominant carrier at St. Pete-Clearwater International Airport, accounting for more than 90 percent of its total flights and propelling the airport to a projected record passenger year in 2015.

But Allegiant's scrappy success is now being questioned by its pilots, who say they are worried about repeated mechanical problems with the airline's fleet of older planes, poor maintenance operations and a culture where profits come before safety.

Read more at the Tampa Bay Times.