The deal made United the world's biggest carrier, until the 2013 tie-up that created American Airlines Group Inc., and was marked by struggles to achieve financial benefits as quickly as American and Delta Air Lines Inc. did when they found merger partners. Switching Industries Munoz, 56, comes to the airline industry after serving as second-in-command at the largest railroad in the Eastern U.S. He told United employees in a letter Tuesday: "I recognize that this news is unexpected, and I want you to hear it directly from me, as United's new CEO." Munoz, who graduated from the University of Southern California and earned an MBA from Pepperdine University, in February was named president of CSX, prompting analysts and investors to consider him as the heir to CEO Mike Ward, 65. Munoz served as chief financial officer at the Jacksonville, Florida-based railroad for almost nine years before becoming COO in 2012.