HUMAN FACTORS MODELS

(a)              Fundamentals of human factors are better understood by different models postulated by experts.

(b)              In this section, some models of human factors will be highlighted as a beginning of the basic elements of the subject.

 The SHEL Model

(a)      Perhaps the most common way of expressing complex systems is to use simple models to illustrate the ideas. In aviation, Elwyn Edwards (1972) proposed the SHEL model to identify the components and interactions within our complex industry (see Figure 1.1).

 

Figure 1.1: Shel Model

(b)     The acronym identifies the components with the following meanings:

Software: manuals, rules, procedures, spoken words, etc., which are part and parcel of standard operating procedures in an organization;

Hardware: aircraft, machinery, tools, control and display systems;

Environment: physical, social and economic climate in which the organization and individuals operate; and

Liveware: the human beings i.e. engineers, flight crew, cabin crew, ground crew, management and administration people - in the system.

(a)              Interactions between components are represented in the model by interfaces. There are 3 interfaces in SHEL model: Liveware-software, liveware-hardware, and liveware-environment (see Figure 1.1), Human factors concentrates on theses interfaces and - from a safety viewpoint, on the elements that can be deficient, e.g.:

Deficiency in S: likelihood of misinterpretation of procedures, badly written manuals, poorly designed checklists, untested or difficult-to-use computer software etc.

Deficiency in H: not enough tools, inappropriate equipment, poor aircraft design for maintainability etc.

Deficiency in E: Uncomfortable workplace, inadequate hangar space, extreme temperatures, excessive noise, poor lighting etc.

Deficiency in L (the central component): Shortage of manpower, lack of knowledge or skill, lack of supervision, lack of support from managers, general nature of human fallibility and so on.

Note: Practical deficiencies may be identified/listed by participants that they experience in their own working environment and their impact on performance may be highlighted for realization.

(a)              Notably, Liveware is at the hub of the SHEL model. Liveware has to interact with other elements in the model forming the interfaces: Liveware-Hardware, Liveware-Software, Liveware-Environment. Suitable design and matching of the interfacings is very important to have optimum level in the performance output in the working system. 

Although modern aircraft are now designed to embody the latest self-test and diagnostic routines that modern computing power can provide, one aspect of aviation maintenance has not changed: maintenance tasks are still being done by human beings. However, man has limitations. Re-designing of aircraft with modern manufacturing techniques are making the aircraft more and more reliable but it is not possible to re-design the human being: we have to accept the fact that the human being (liveware) is intrinsically unreliable due to its natural tendency of fallibility. However, we can guard against this unreliability of human by careful design and suitable matching in the interfaces to assist his performance and respect his limitations. If these two aspects are ignored, the human - in this case the maintenance engineer - will not perform to the best of his abilities, may make errors, and may jeopardize safety.

          Liveware-Hardware: This interface is most commonly known as the human-machine systems e.g. the design of seats to fit the sitting characteristics of the human body; design of displays to match the sensory and information-processing characteristics of the user; design of controls with proper movement, force and location.

Deficiency in this interface (L-H deficiency) is to be removed to reduce the error rate. Controls that require extreme physical strength, displays that are easy to misread and hours of boring monitoring contribute to high error rates in this interface.

User-friendly controls and displays and a better understanding of the relative strengths of humans and machines provide a platform for reducing error rates considerably.

Human Factors ergonomically deals with issues arising from this interface.

Liveware-Software: This encompasses the interface between humans and the non-physical aspects of the system such as procedures, manual and checklist layout, symbology, and computer programs. The problems may be less tangible than those involving the L-H interface and consequently more difficult to detect and resolve (e.g. misinterpretation/misunderstanding of technical literature or symbology). Many of the manuals engineers were expected to use were not user friendly, policies were interpreted differently by different supervisors and rules were often ignored because they conflicted with common sense.

Liveware-Environment In the maintenance of aircraft, environment ranges from physical environment (e.g. noise, light, temperature, humidity etc) of working place to broad managerial, political, and economic constraints of the organization. These aspects of the environment interact with the human via this interface. Although modifications to some of these factors may fall beyond the function of Human Factors practitioners, they should be considered and addressed by those in management with the ability to do so.