When a plane goes down, the initial concern is to find survivors and save lives. But immediately thereafter the focus changes to assessing the cause. It is vital for investigators to find the reasons behind crashes so that similar disasters can be prevented. But the causes of airplane crashes today are rarely traced to just one problem, and they are not easy to determine amidst the chaos and wreckage of a downed airplane. Complex factors generally combine to bring down a plane. Bad weather, like thunderstorms or fog, can compound pilot error, while small mechanical problems can affect other aspects of a plane's ability to function. In many cases, planes have flaws that may not be discovered until after disaster strikes. Still, investigators have done remarkable work in making sense of perplexing crashes, and as a result many safety features are regularly...