Describing and Probing Complex System Behavior: A Graphical Approach

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Describing and Probing Complex System Behavior: A Graphical Approach

Bachelder, Edward / Leveson, Nancy

Hands-on training and operation is generally considered the primary means that a user of a complex system will use to build a mental model of how that 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 presents 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 fundamental goal of the model is to capture and present critical interactive aspects of a complex system in an integrated, intuitive fashion. This graphical approach is applied to an actual military helicopter system, using the onboard hydraulic leak detection/isolation system as a testbed. The helicopter Flight Manual is used to construct the system model, whose components include: logical structure (waiting and checking states, transitional events and conditions), human/automation cross communication (messages, information sources), and automation action and associated action limits. Using this model, examples of the following types of mode confusion are identified in the military helicopter case study: 1) Unintended side effects, 2) Indirect mode transitions, 3) Inconsistent behavior, 4) Ambiguous interfaces, and 5) Lack of appropriate feedback. The model also facilitates analysis and revision of emergency procedures, which is demonstrated using an actual set of procedures.