When Russia’s United Aircraft Corp. (UAC) launched its new single-aisle aircraft MS-21, its ambitions were clear. The aircraft’s name, Magistralny Samoljot 21 Veka, means “mainline aircraft of the 21st century.” The company was not alluding to mainline routes within Russia. It was thinking global. After all, Irkut President Oleg Demchenko believes the aircraft is “the best in its class”—a class...