While it is impossible to reduce chaotic systems to individual factors, and it is likewise impossible to predict the effect of an individual factor upon the system as a whole, it is certainly possible for one factor with a global effect to move the entire system towards or away from a probable outcome.<p>If we postulate that, now absent the selection pressures that have shaped human intelligence over the last few million years or so, human intelligence is likely to decline, then we can ask ourselves where this decline might be likely to first show up in the chaotic system of human endeavour.<p>One possible answer is that it will appear first at the boundary layers: the places where a critical level of human intelligence is required to keep a complicated task operating.<p>I propose that flying passenger aircraft is such a task. A critical level of intelligence must be maintained by a very large number of people in order to keep passenger aircraft in the air. Everyone, from designers to manufacturers, to QC, to maintenance to pilots to airline management has to function above a certain critical level to perpetuate the activity.<p>It is possible that clusters of aircraft accidents are purely random and part of the complex system that is air travel. However, it is possible that clusters of aviation accidents represent crossings of the boundary layer resulting from the change in a global factor, like human intelligence, that has moved the entire system probabilistically.<p>The details of some recent accidents should give us pause. The series of over-control/mis-control accidents including AF447, Colgan Air and others defy reasonable explanation, and they appear to have no precedent in recent passenger aviation. MH370 and MH17, so far as we can see, have no reasonable explanation other than unaccountable human behaviour (failing to communicate over the course of seven hours flying in the case of MH370, and navigating over a war zone in the case of MH17).<p>It is possible, although certainly not provable at this point, that we are simply becoming too stupid (in general) to fly passenger aircraft safely. It may be time to switch to fully automated aircraft systems.