Spirit Airline, Inc.’s (SAVE) upbeat air-travel demand is boosting its top line. The company’s efforts to upgrade its fleet are commendable. However, SAVE is grappling with major headwinds like high operating expenses and high capex, which are adversely impacting its bottom line.Factors Favoring SAVEDriven by an uptick in leisure air travel demand, Spirit Airlines' consolidated traffic, measured in revenue passenger miles, has been significantly rising, boosting the company's capacity. As a result, availabl ...