(August 2011) It has often been said that accidents result not from one big cause, but from a lot of little ones that happen to converge in some unforeseen way. Nevertheless, many fatal accidents do arise from one simple cause: VFR pilots flying into IFR weather. This happens so regularly, and in so monotonous a pattern, that I seldom write about it, since there seems to be so little to say about any given instance. I prefer, if one can be said to prefer one type of sad event to another, to examine accidents whose causes are more complex and thought provoking.
Another truism is that mechanical failures are comparatively rare; most accidents are precipitated by some pilot action or omission. Such mechanical failures as do occur fall into various categories — materials failures, maintenance errors and so on. Of these categories, one of the least populous, but of the greatest practical interest, is that of accidents that are due to engineering. These accidents arise from unexpected interactions of seemingly benign or unrelated design features. This is the soil in which certification requirements, and liability lawsuits, sprout and proliferate.
