The system creates ragged edges that don’t fit.
The human component is at the center of the SHELL model that represents the modern air transportation system. This is a critical and flexible component in the system, interacting directly with other system components, namely Software, Hardware, Environment and Liveware. Human senses for collecting vital task and environment-related information are subject to performance. A human sense does not detect the whole range of sensory information available. The circadian rhythm and emotions are triggers for variations in human performance. Humans are variables in information processing effectiveness and influenced by motivation. E.g. aircraft display, instrument and alerting, or warning system design are engineered to reduce the effect of these variables. After sensing and processing information, the output involves decisions, muscular action and communication. Design considerations include aircraft control-display movement relationship, acceptable direction of movement of controls, control resistance and coding, acceptable human forces required to operate aircraft doors, hatches and cargo equipment and speech characteristics in the design of voice communication procedures.
The key to success is not in the edges but within the system itself.
The concept of SMS that we don’t manage risks; we lead personnel, manage equipment and validate operational design for improved performance above the safety risk level bar is strengthen by including the SHELL model in a root cause analysis and risk assessment. A lesson learned from the SHELL model is that it comes with ragged edges, which also is characteristics of an effective SMS.