A graphical language for describing complex system behavior: applications to design, training and user operation

Operator manuals of complex systems involving human-machine interaction largely employ text to convey knowledge of the system. The occasional diagram intending to integrate portions of the text typically focuses on mechanical/electrical component interaction - a schematic of the automation logic is a rare finding. When the automation is diagrammed, it is usually presented as a stand-alone system that communicates only with itself. The communication between human and machine is often explained separately in tabular form, given as a listing of stimulus and associated meaning. While such a piecewise presentation can impart eventual understanding of the system to an operator, hands-on training and operation is generally considered the primary means for building a mental model of how a system works. However, accidents abound where a major contributing factor was user disorientation/misorientation with respect to the automation behavior, even when the operator was a seasoned user. This paper will present a compact graphical method that can be used to describe system operation, where the system may be composed of interacting automation and/or human entities. The graphical approach is applied to an actual commercial aircraft system, using the descent flight phase as a testbed. Cockpit and flight management system manuals are used to construct the system model, whose fundamental goal is to capture and present critical interactive aspects of a complex system in an integrated, intuitive fashion. Potential applications of this model to design, training and user operation are presented, and various instances of potential mode confusion are identified in the commercial aircraft case study.