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 airports as 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. 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. In fact, the International Civil Aviation Organisation has described human factors as a concept of people in their living and working situations; their interactions with machines (hardware), procedures (software) and the environment about them; and also their relationships with other people. 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 characterised by mismatches at interfaces between system components, rather than catastrophic failures of individual components. Interfaces Liveware-Software (L-S) Interaction between human operator and non-physical supporting systems in the workplace. Involves designing software to match the general characteristics of human users and ensuring that the software (e.g. rules/procedures) is capable of being implemented with ease. During training, flight crew members incorporate much of the software (e.g. procedural information) associated with flying and emergency situations into their memory in the form of knowledge and skills. However, more information is obtained by referring to manuals, checklists, maps and charts. In a physical sense these documents are regarded as hardware however in the information design of these documents adequate attention has to be paid to numerous aspects of the L-S interface. For instance, by referring to cognitive ergonomics principles, the designer must consider currency and accuracy of information; user-friendliness of format and vocabulary; clarity of information; subdivision and indexing to facilitate user retrieval of information; presentation of numerical data; use of abbreviations, symbolic codes and