MOST PILOTS HAVE seen the video of the United Airlines' DC -10 cartwheeling down Runway 22 at Sioux City, Iowa, in 1989. It is a sight unlikely to be forgotten. The accident was caused by the catastrophic loss of all hydraulic power, which made it impossible to move any of the flight controls. There are no backup cables with which to manually control a widebody jetliner. Not even an Olympic weightlifter could operate such massive control surfaces. The stabilator on a Lockheed L-1011, for example, weighs 7,000 pounds. Captain Al Haynes and his crew discovered that the only way to control their crippled DC-10 was to vary the thrust of the two underwing engines. (The uncontained failure of the center engine in the tail caused the loss of fluid from all three hydraulic systems.)
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