The human operator as an essential component

As technology progresses the safety of man-machine systems depends more and more on the quality of the human component (operator). This fact is very obvious in transportation, where the operator (driver) is formally and actually in control of his or her vehicle. In aviation, however, a strong trend towards software control of the aeroplane is already becoming dominant, forcing the operator (pilot) primarily into the role of supervisor or monitor of the automatic control system and into that of trouble-shooter in case of (technical) failure. In this respect a cockpit crew is facing the same situation as for instance a shift of operators in the central control room of a completely computerised chemical process plant. 

This development does not mean that we are on our way towards industrial systems without production staff or transportation systems without drivers Or pilots. 

The human operator will continue to play an essential part in the safety of such complex systems because of several inherent limitations of software control  

Only those situations can be handled by software which are foreseen in the design phase and for which software solutions have been found and implemented. Since a substantial part of accidents (Wagenaar and Groeneweg, 1987) happen precisely because of unforeseen or impossible circumstances, the flexible human operator will have to be present in order to cope with these, even though he will have difficulties in doing so pre-sicely because of those same reasons, 

Even the safe handling of foreseen problems is never completely guaranteed, because software, being the result of a complex human activity, will always contain (hidden) errors. The human operator will then have to be able to control the system manually. 

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