Four jetliners, two of them flights by American Airlines and two by United Airlines, had taken off from three U.S. airports on the morning of Sept. 11, 2001, unknowingly to become part of the 9/11 attack and the greatest aviation tragedy in American history.
At 9 a.m. Friday, United will mark the moment a quarter century ago with a flyover at its flight-training center in Denver by a Boeing 777 accompanied by four F-16 fighters from the Colorado Air National Guard.
A private memorial event for United employees at the training center will include the unveiling of a monument honoring crews aboard United Flight 175 and Flight 93, created from steel recovered from the World Trade Center wreckage in New York. The monument will stand 9 feet 11 inches…