Principle 5. Resources and Constraints

Principle 5. Resources and Constraints


Success depends on adequate resources and appropriate constraints

Consider the adequacy of staffing, information, competency, equipment, procedures and other resources, and the appropriateness of rules and other constraints

"Any attempt to understand human work needs to consider resources and constraints carefully." Image: Randomwire CC BY-NC-SA 2.0

Meeting demand is only possible with adequate resources and appropriate constraints. These are system conditions which help or hinder the work. Resources are needed or consumed while a function is carried out (Hollnagel, 2012), and include personnel, competence, procedures, materials, software, tools, equipment, information and time. Resources are provided by ‘foreground’ functions and activities (such as the production of a flight progress strip) and by ‘background functions’ such as the provision of documentation and procedures, materials, and equipment.

The quality of resources varies over the short- and long- term, and unavailable or inadequate resources make it difficult to meet demand effectively. For instance, a procedure may be out of date; flight strips may be produced for each waypoint, requiring an Assistant to sort them and keep only those that are relevant; an FDP system may be unreliable; lack of staff for an operational position may lead to a delay in opening a new sector until on-call staff arrive.

To cope with variable demand and variable resources, people make trade-offs and vary their own performance by adjusting and adapting. These are essential aspects of human performance in the context of the system. Occasionally, there may be unwanted performance variability, for instance in cases of competency gaps or fatigued staff. There may also occasionally be trade-offs with unwanted consequences. More often, though, the trade-offs and performance variability give the system the flexibility that is required in order to meet demand.

Resources, like demands and goals, are an important system lever for change. Improving resources improves the ability to meet demand, but this often takes time – sometimes too much time to be realistic in dynamic operational situations. In these cases, improving the flow of work in the short term may be a more effective system lever.

One way to do this is to rationalise constraints. Performance is usually subject to various constraints or controls that supervise, regulate or restrict the flow of activity. Constraints usually seek to suppress variability or keep it within certain boundaries. Constraints are necessary for system stability, but can limit flexibility. Constraints may be exercised by people (e.g. supervision, inspection, checking), or be associated with procedures (e.g. standard operating procedures, checklists) and equipment (e.g. confirmation messages, dialogue boxes). A constraint may be a dynamic output from another activity (e.g. a check or readback-hearback), or may be relatively stable and relate to a resource.

Safety management is often characterised by the imposition of constraints. But this approach runs into limits. Constraints often restrict necessary performance variability, as well as unwanted variability, affecting the ability to achieve goals. If constraints run counter to the purpose and flow of work, they become problematic, and people work around constraints or ‘game the system’ in ways that are not visible from afar.

Any attempt to understand human work needs to consider resources and constraints carefully. This means understanding the state of resources (for normal operations or at the time of any particular event), and the variability of resources over time, since history will shape expectations and hence the local rationality of field experts. As an example, if an alert was functioning as designed at the time of an occurrence, but had a history of false alerts, then the history of variability will influence field experts’ understandings of the dependability of the alert in the present.

Practical advice

  • Consider the adequacy of resources. With field experts, consider how resources (staff, equipment, information, procedures) help or hinder the ability to meet demand, and identify where there is the opportunity for improvement.
  • Consider the appropriateness of constraints. Consider the effects of constraints (human, procedural, equipment, organisational) on flow and system performance as a whole. Reflect on the implications for individuals and the system when people have to work around constraints in order to meet demand.

View from the field

Mihály Kurucz Head of Safety Division, Hungarocontrol, Hungary

“Improving system performance requires a delicate interplay between resources. In all parts of the organisation, you will rely on the right people, procedures and equipment to run an effective system. But resources and constraints are closely linked. For instance, equipment should not over-constrain people, but rather allow the flexibility to meet demands and achieve goals. Safety-related regulations and procedures support the performance of the organisation, but I think over-regulation – be it external or internal – is a counterproductive constraint. In my view the best rules and procedures show the goals and principles, but don’t necessarily define directly and exactly the actions that you must do. Effective safety performance ultimately relies on the knowledge and sense of professionals at all levels, and their freedom to choose the most effective solution to a specific situation.”

Source: Systems Thinking for Safety: Ten Principles. A White Paper. Moving towards Safety-II, EUROCONTROL, 2014.

The following Systems Thinking Learning Cards: Moving towards Safety-II can be used in workshops, to discuss the principles and interactions between them for specific systems, situations or cases.

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