>[!abstract] >In aviation, the SHELL (or SHEL) model is a conceptual model of human factors that helps to clarify the location and cause of human error within an aviation environment. > >It is named after the initial letters of its components (Software, Hardware, Environment, Liveware) and places emphasis on the human being and human interfaces with other components of the aviation system. > >The SHELL model adopts a systems perspective that suggests the human is rarely, if ever, the sole cause of an accident. The systems perspective considers a variety of contextual and task-related factors that interact with the human operator within the aviation system to affect operator performance. As a result, the SHELL model considers both active and latent failures in the aviation system. > >The four components of the SHELL model or aviation system do not act in isolation but instead interact with the central human component to provide areas for human factors analysis and consideration. The SHELL model indicates relationships between people and other system components and therefore provides a framework for optimising the relationship between people and their activities within the aviation system that is of primary concern to human factors. > >According to the SHELL model, a mismatch at the interface of the blocks/components where energy and information is interchanged can be a source of human error or system vulnerability that can lead to system failure in the form of an incident/accident. Aviation disasters tend to be characterized by mismatches at interfaces between system components, rather than catastrophic failures of individual components. > >## Software >- Non-physical, intangible aspects of the aviation system that govern how the aviation system operates and how information within the system is organized. >- Software may be likened to the software that controls the operations of computer hardware. >- Software includes rules, instructions, aviation law and regulations, policies, norms, orders, safety procedures, standard operating procedures, customs, practices, conventions, habits, symbology, supervisor commands and computer programmes. >- Software can be included in a collection of documents such as the contents of charts, maps, publications, emergency operating manuals and procedural checklists. > >## Hardware >- Physical elements of the aviation system such as aircraft (including controls, surfaces, displays, functional systems and seating), operator equipment, tools, materials, buildings, vehicles, computers, conveyor belts etc. > >## Environment >- The context in which aircraft and aviation system resources (software, hardware, liveware) operate, made up of physical, organisational, economic, regulatory, political and social variables that may impact on the worker/operator. >- Internal air transport environment relates to immediate work area and includes physical factors such as cabin/cockpit temperature, air pressure, humidity, noise, vibration and ambient light levels. >- External air transport environment includes the physical environment outside the immediate work area such as weather (visibility/Turbulence), terrain, congested airspace and physical facilities and infrastructure including airportsas well as broad organisational, economic, regulatory, political and social factors. > >## Liveware >- Human element or people in the aviation system. For example, flight crew personnel who operate aircraft, cabin crew, ground crew, management and administration personnel. >- The liveware component considers human performance, capabilities and limitations. > >(Wikipedia, 2025). >[!related] >- **North** (upstream): — >- **West** (similar): [[IMSAFE checklist]], [[PAVE checklist]] >- **East** (different): — >- **South** (downstream): —