Modes in human-machine systems: Constructs, representation, and classification

This article surveys and discusses human interaction with automated control systems that employ modes. We focus our discussion on the features of the control system that lead to mode confusion and error. We first provide working definitions of the term mode and discuss key constructs that contribute to mode error, such as mode ambiguity and user expectations. Following this, we discuss human interaction with automated control systems in general and cockpit automation in particular. To provide a formal description of human interaction with such control systems, we introduce a modeling language, Statecharts, which is used by system engineers to specify complex control systems. We use the Statecharts language to describe the 3 types of modes that are commonly found in modern control systems: interface, functional, and supervisory modes. Examples from cockpit automation are used to illustrate each type of mode. The article concludes with a brief discussion of the links between the mode constructs and formal representation of human interaction with control systems.