On the other hand, in many cases there is no "smoking gun," the one significant factor that made an accident inevitable. Often experts are unsure what caused a crash, and even the pilot, if he survived, may have no idea what caused the accident or, if it was pilot error, what led him to make the fatal mistake that led to the crash. In the May issue of Flying ("No Greater Burden"), I wrote about how Russ Jeter landed his amphibious floatplane gear-down on a lake, leading to the death of his young son. Jeter, a very careful and professional pilot, was totally mystified as to why he had neglected to do the final GUMP check that he always does to ensure that the gear is up or down as appropriate. It was only after a specialist in human factors gave him a stress test that he realized he had not been sleeping well after the death of his mother and had felt unusually drowsy that morning. That one subtle factor that he was not consciously aware of, combined with a relaxed flight and the distraction of his son asking him questions as he descended to land on the lake, was enough to cause a momentary loss of focus that allowed him to land gear-down.