Swiss cheese model, which is used to investigate the causes of complex accidents, was introduced by James T. Reason from Manchester University in 2000. This model has found use in many fields like engineering, healthcare, emergency service organizations. It is also widely used in aviation to investigate the causes of accidents.
Swiss cheese model is the model that defines accidents and incidents in aviation. The integrated structure in the accidents is compared to the holes in Swiss cheese. According to this model, which is accepted by many aviation authorities such as ICAO, there is no single cause of any accident. Accidents occur as a result of cumulative effects. In accidents, the company, technical staff, air traffic controllers, pilots, the pilot’s family life, the decisions taken and the underlying reasons should be discussed collectively in an organized manner. In this model, various layers and holes on these layers and pathogens are defined. The overlap of these holes end up with incidents.
Swiss cheese model proposes that most of the accidents can be traced by one or more of four layers of failure. These layers are;
- Organizational influences,
- Unsafe supervision,
- Preconditions for unsafe acts, and
- The unsafe acts themselves.
In most accidents, a layer is able to stop the catastrophic accident. Holes may appear, disappear or vary in size depending on the mental and physical nature of the system or organization. Although the apparent causes of the accidents seem to be the cause, there can be lots of also hidden errors behind the accidents.
An Example – Swiss Cheese Model
Let’s consider an imaginary disaster. Two planes collide on the runway with a wrong instruction from an air traffic controller working in the control tower at the airport (of course, the reasons for the events may not be so clear and precise). The apparent reason is obvious. The controller gave an incorrect instruction causing an accident. However, when we examine the incident, we can see that perhaps the controller worked long hours due to lack of personnel and therefore his decision-making ability was weakened. Even if we investigate the reason for the ATC staff shortage, we can find out that the company does not employ enough personnel due to financial concerns. If we examine this attitude of the company, we can see that the company behaves in this way, perhaps because of the insufficient auditing and rules of the airspace authority.
Beyond the apparent causes, there may be many latent conditions that cause the accident. In this example there are 4 layers of cheese that caused the accident. As can be understood from our case study, the problems experienced in all layers cause accidents. If the airspace authority sets stricter rules and conducts proper controls, perhaps the chain of errors will end in that layer without ever passing to the other layer. Swiss cheese model proposes to approach events in this way and to handle them with a holistic method.
Going back to our case, we cannot completely solve the problem by only penalizing the controller who made the mistake. Because the controller that will replace it under the same conditions may make a similar error after a while. Therefore, it is necessary to focus on the underlying causes in order to solve the problem completely.
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