Perhaps the classic example of a failed flight control system involves United Airlines Flight 232, a scheduled domestic passenger operation of a DC-10. On July 19, 1989, while in cruise at FL370, the jet’s center, tail-mounted engine’s fan disk failed. The pieces penetrated the engine’s containment shroud and severed the airplane’s hydraulic lines. Those lines quickly leaked out their fluid, eliminating any ability for the flight crew to reposition the airplane’s primary control surfaces.
Using the only controls remaining—the left and right engines’ throttles—the crew managed to descend and approach the Sioux Gateway Airport/Col. Bud Day Field in Sioux City, Iowa, where the DC-10 crash-landed, killing 111 of the passengers and crew aboard. Survivors totaled 185, including the flight crew. Many lessons were learned from this accident, including alternatives to aircraft control when the primary systems have failed. To understand them, though, we first have to understand the systems themselves.
