Guidelines for Establishing a Safety Management System on Aerodromes. DASS Publication 11/2006-A APPENDIX 9 HUMAN FACTORS 1,2 AND THE SHELL MODEL

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1 APPENDIX 9 HUMAN FACTORS 1,2 AND THE SHELL MODEL A9.1 In a high-technology industry such as aviation, the focus of problem solving is often on technology. However, the accident record repeatedly demonstrates that at least three out of four accidents involve performance errors made by apparently healthy and appropriately qualified individuals. In the rush to embrace new technologies, the people who must interface with and use this equipment are often overlooked. A9.2 The sources of some of the problems causing or contributing to these accidents may be traced to poor equipment or procedure design, or to inadequate training or operating instructions. Whatever the origin, understanding normal human performance capabilities, limitations and behavior in the operational context is central to understanding safety management. An intuitive approach to Human Factors is no longer appropriate. A9.3 The human element is the most flexible and adaptable part of the aviation system, but it is also the most vulnerable to influences that can adversely affect its performance. With the majority of accidents resulting from less than optimum human performance, there has been a tendency to merely attribute them to human error. However, the term human error is of little help in safety management. Although it may indicate where in the system the breakdown occurred, it provides no guidance as to why it occurred. A9.4 An error attributed to humans may have been design-induced or stimulated by inadequate equipment or training, badly designed procedures, or a poor layout of checklists or manuals. Furthermore, the term human error allows concealment of the underlying factors that must be brought to the fore if accidents are to be prevented. In modern safety thinking, human error is the starting point rather than the stopping point. Safety management initiatives seek ways of preventing human errors that might jeopardize safety, and ways of minimizing the adverse safety consequences of the errors that will inevitably occur. This requires an understanding of the operating context in which humans err (i.e. an understanding of the factors and conditions affecting human performance in the workplace). SHEL model A9.5 The workplace typically involves a complex set of interrelated factors and conditions, which may affect human performance. The SHEL model (sometimes Page no.: App. 9-1

2 1. Adapted from the ICAO Human Factors Guidelines for Safety Audits Manual (Doc 9806), Chapter Refer to the ICAO Human Factors Training Manual (Doc 9683) for a more comprehensive coverage of the theoretical and practical aspects of Human Factors. referred to as the SHELL model) can be used to help visualize the interrelationships among the various components of the aviation system. This model is a development of the traditional man-machine-environment system. It places emphasis on the human being and the human s interfaces with the other components of the aviation system. The SHEL model s name is derived from the initial letters of its four components: a) Liveware (L) (humans in the workplace); b) Hardware (H) (machine and equipment); c) Software (S) (procedures, training, support, etc); and d) Environment (E) (the operating circumstances in which the rest of the L-H-S system must function) A9.6 Figure A9-1 depicts the SHEL model. This building block diagram is intended to provide a basic understanding of the relationship of the human to other factors in the workplace. Page no.: App. 9-2

3 Figure A9-1 SHELL MODEL A9.7 Liveware. In the center of the SHEL model are those persons at the front line of operations. Although people are remarkably adaptable, they are subject to considerable variations in performance. Humans are not standardized to the same degree as hardware, so the edges of this block are not simple and straight. People do not interface perfectly with the various components of the world in which they work. To avoid tensions that may compromise human performance, the effects of irregularities at the interfaces between the various SHEL blocks and the central Liveware block must be understood. The other components of the system must be carefully matched to humans if stresses in the system are to be avoided. A9.8 Several different factors put the rough edges on the Liveware block. Some of the more important factors affecting individual performance are listed below: a) Physical Factors: These include the individual s physical capabilities to perform the required tasks, e.g. strength, height, reach, vision and hearing. b) Physiological factors: These include those factors which affect the human s internal Page no.: App. 9-3

4 physical processes, which can compromise a person s physical and cognitive performance, e.g. oxygen availability, general health and fitness, disease or illness, tobacco, drug or alcohol use, personal stress, fatigue and pregnancy. c) Psychological factors: These include those factors affecting the psychological preparedness of the individual to meet all the circumstances that might occur, e.g. adequacy of training, knowledge and experience, and workload. The individual s psychological fitness includes motivation and judgment, attitude towards risky behavior, confidence and stress. d) Psycho-social factors: These include all those external factors in the social system of individuals that bring pressure to bear on them in their work and non-work environments, e.g. an argument with a supervisor, labormanagement disputes, a death in the family, personal financial problems or other domestic tension. A9.9 The SHEL model is particularly useful in visualizing the interfaces between the various components of the aviation system. These include: a) Liveware-Hardware (L-H). The interface between the human and the machine (ergonomics) is the one most commonly considered when speaking of Human Factors. It determines how the human interfaces with the physical work environment, e.g. the design of seats to fit the sitting characteristics of the human body, displays to match the sensory and information processing characteristics of the user, and proper movement, coding and location of controls for the user. However, there is a natural human tendency to adapt to L-H mismatches. This tendency may mask serious deficiencies, which may only become evident after an accident. Page no.: App. 9-4

5 b) Liveware-Software (L-S). The L-S interface is the relationship between the individual and the supporting systems found in the workplace, e.g. the regulations, manuals, checklists, publications, SOPs and computer software. It includes such user friendliness issues as currency, accuracy, format and presentation, vocabulary, clarity and symbology. c) Liveware-Liveware (L-L). The L-L interface is the relationship between the individual and other persons in the workplace. Flight crew, ATCOs, AMEs and other operational personnel function as group, and group influences play a role in determining human behavior and performance. This interface is concerned with leadership, cooperation, teamwork and personality interactions. The advent of crew resource management (CRM) has resulted in considerable focus on this interface. CRM training and its extension to ATS (team resource management (TRM)) and maintenance (maintenance resource management (MRM)) promote teamwork and focus on the management of normal human errors. Staff/management relationships are also within the scope of this interface, as are corporate culture, corporate climate and company operating pressures, which can all significantly affect human performance. d) Liveware-Environment (L-E). This interface involves the relationship between the individual and the internal and external environments. The internal workplace environment includes such physical considerations as temperature, ambient light, noise, vibration and air quality. The external environment (for pilots) includes such things as visibility, turbulence and terrain. Increasingly, the 24/7 aviation work environment includes disturbances to normal biological rhythms, e.g. sleep constraints, which in turn affect the overall corporate Page no.: App. 9-5

6 environment. Included here are such factors as the adequacy of physical facilities and supporting infrastructure, the local financial situation, and regulatory effectiveness. Just as the immediate work environment may create pressures to take short cuts, inadequate infrastructure support may also compromise the quality of decision-making. A9.10 Care needs to be taken in order that problems (hazards) do not fall through the cracks at the interfaces. For the most part, the rough edges of these interfaces can be managed, for example: a) The designer can ensure the performance reliability of the equipment under specified operating conditions. b) Adhering to JCAA s defined conditions under which the equipment may be used. c) The airport operator s management can specify SOPs and provide initial and recurrent training for the safe use of the equipment. d) Individual equipment operators can ensure their familiarity and confidence in using the equipment safely under all required operating conditions. Page no.: App. 9-6