For most of the past decade, 
Delta Air Lines has been the unquestioned leader in the commercial aviation industry. The carrier has been the first to innovate in key areas, has drastically reshaped the definition of a successful airline loyalty program through its valuable partnership with American Express, and has consistently boasted the industry’s best financial returns. For the majority of the past ten years, American Airlines and United Airlines, the carrier’s two most important rivals, have mostly been playing catch-up.