Alternate title: "Mystery Crashes" The Boeing B-737 is the most reliable plane in the world. But in 1991, United Airlines Flight 585's rudder fails and the plane nosedives during approach. Investigators know nothing about what caused it. T hen in 1994, USAir Flight 427 crashes in the same way after take-off. What is causing the crashes? Is there a Hidden Danger in every B-737 in the world?