SHELL model

[1]: 3 [4] The SHELL model adopts a systems perspective that suggests the human is rarely, if ever, the sole cause of an accident.

[2] Each component of the SHELL model (software, hardware, environment, liveware) represents a building block of human factors studies within aviation.

[7] The human element or worker of interest (liveware) is at the centre or hub of the SHELL model that represents the modern air transportation system.

Humans require food, water and oxygen to function effectively and deficiencies can affect performance and well-being.

[2] Humans have limitations in information processing capabilities (such as working memory capacity, time and retrieval considerations) that can also be influenced by other factors such as motivation and stress or high workload.

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.

[2] People function effectively only within a narrow range of environmental conditions (tolerable for optimum human performance) and therefore their performance and well-being is affected by physical environmental factors such as temperature, vibration, noise, g-forces and time of day as well as time zone transitions, boring/stressful working environments, heights and enclosed spaces.

A diagram showing the SHELL model components as building blocks. Liveware is in the middle, surrounded by Software, Hardware, Environment and Liveware. A note reads, "In this model the match or mismatch of the blocks (interface) is just as important as the characteristics of the blocks themselves. A mismatch can be a source of human error."
The SHELL model