A Northwest Airlines passenger liner takes off from Detroit, fails to gain altitude, yaws and descends, and crashes on a highway, killing all aboard except a four-year-old girl.
Investigators are all over the site of the crash and the wreckage itself, eliminating possible reasons one by one. Weather? No. Airplane overloaded for a short runway? No.
Finally they determine that the take off was made with flaps and slat fully retracted. An airplane can't take off with those settings. And here is gets interesting, in the way a Sherlock Holmes mystery is fascinating. They follow the same methods of analysis as the Mayo clinic does in treating a medical condition. They ask, "Why?" How could an experienced aircrew make such an elementary blunder?
Okay, the flaps and slats forced the crash, but that's what Aristotle would have called the material explanation. The investigators look beyond that, for the efficient explanation -- what caused the flaps and slats to be in that position? As usual, there was more than one factor behind the failure to deploy flaps and slats. The solutions to the problems was surprisingly simple.