Overview: Three mysterious accidents send investigators hunting for clues. In the end, all three trails lead back to the same source-the fuel tank. Minutes before touching down in Portland, United Airlines 173 loses all four engines over a densely populated suburb. In Japan, a Boeing 737 lands safely, but then catches fire with all 165 passengers and crew still on board. And, nearly 700 miles off course, the crew of Varig Flight 254 are forced to make a crash landing in the Amazon jungle.