Frederic Melton
The Swiss Cheese Model is a theory that explains accidents as the result of multiple interrelated factors, rather than a single cause. It likens an organisation's defences against failure to slices of Swiss cheese, with holes representing weaknesses in the system. When the holes momentarily align, a trajectory of accident opportunity is created, and a failure occurs. This model has been applied to aviation accidents, including the Lion Air Flight 610 crash, where nine factors contributed to the accident, and another incident involving Malaysia Airlines, where pitot tubes were found to be covered. These incidents serve as examples of how the Swiss Cheese Model can be used to understand the complex causes of accidents and improve safety measures.
| Characteristics | Values |
|---|---|
| Date of Incident | 29 October 2018 |
| Aircraft | Lion Air Flight 610 |
| Origin | Soekarno-Hatta International Airport, Jakarta |
| Destination | Depati Amir Airport, Pangkal Pinang |
| Number of Passengers | 189 |
| Cause of Accident | Faulty sensor repair process, poor maintenance, inadequate training for the captain and first officer, etc. |
| Contributing Factors | 9 factors, including certification issues, maintenance issues, poor Crew Resource Management, etc. |
| Model Used for Analysis | Swiss Cheese Model |
| Description of Model | A model of accident causation that views accidents as the result of multiple factors, with each factor representing a layer of Swiss cheese with holes that must align for an accident to occur |
| Types of Failures | Active failures (direct, immediate consequence) and latent failures (organizational factors that predispose active failures) |
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What You'll Learn
The Swiss Cheese Model of accident causation
The Swiss Cheese Model likens human systems or an organization's defences against failure to multiple slices of Swiss cheese, with holes of varying sizes and positions in each slice. These holes represent weaknesses or potential failure points in the system. The slices of cheese are the barriers or layers of defence that protect against risks. When the holes in each slice align, a "trajectory of accident opportunity" is created, allowing a hazard to pass through and resulting in a failure. This illustrates that accidents are typically caused by a combination of factors rather than a single root cause.
In the context of aviation accidents, the Swiss Cheese Model suggests that there is not just a single cause of any given accident. Instead, threats arise from the cumulative effects of multiple breaches in different layers of defence. These layers can include the company, technical staff, air traffic controllers, pilots, the pilot’s personal life and physical health, the decisions made by authorities, and the rules and regulations in place. For example, consider a scenario where two planes collide on a runway due to an incorrect instruction from an air traffic controller. While the apparent cause may be the controller's error, investigating further may reveal that the controller was working long hours due to staff shortages, which in turn could be attributed to the company's financial concerns.
The Swiss Cheese Model identifies two types of failures: active failures and latent failures. Active failures are immediate consequences that directly cause accidents and are typically made by front-line personnel such as pilots, maintenance technicians, and ground support equipment operators. Latent failures are organizational factors that predispose the system to active failures. Examples of latent failures include uncertainties in roles and responsibilities, management issues, and inadequate safety programs. Latent failures are crucial for accident prevention because they can influence multiple potential errors, and addressing them can be a cost-effective way to prevent accidents.
By understanding the Swiss Cheese Model, organizations can gain insights into why accidents occur despite their best efforts to prevent them. It helps to identify weak points and develop strategies to strengthen defences and reduce the likelihood of accidents.
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Active and latent failures
The Swiss Cheese Model, developed by Professor James Reason in the 1990s, is a model of accident causation that is widely used in aviation safety. It posits that accidents are not the result of a single cause but rather the cumulative effects of multiple factors, with each factor representing a layer of Swiss cheese with holes (weaknesses) that must align for an accident to occur.
The model distinguishes between active and latent failures. Active failures are the unsafe acts or human errors that directly cause an accident. These are typically made by front-line personnel such as ground support equipment operators, maintenance technicians, and aircraft pilots. Latent failures are organisational weaknesses that predispose the system to active failures. Examples include uncertainties in roles and responsibilities and inadequate training. Latent failures are important to address because they can influence multiple potential errors, and removing them can be a cost-effective way to prevent accidents.
An example of an active failure is the incorrect instruction given by an air traffic controller that results in two planes colliding on the runway. The latent failure in this case could be that the controller was working long hours due to a staffing shortage, which in turn could be caused by the company's financial concerns.
Another example of an aviation incident that can be analysed through the Swiss Cheese Model is the Lion Air Flight 610 crash. In this case, the active failures included poor crew resource management and inadequate training for the captain and first officer. The latent failures included poor maintenance practices and a faulty sensor repair process.
The Swiss Cheese Model helps to illustrate that accidents are rarely the result of a single point of failure but rather the alignment of multiple weaknesses in the system. By understanding the interplay between active and latent failures, organisations can develop more robust systems and strategies to prevent future accidents.
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Multiple factors and defences
The Swiss Cheese Model, also known as Swiss Cheese Model Risk Management, was first proposed by Professor James Reason in 1990 at the University of Manchester. The model is used in risk analysis and risk management and is widely applied in aviation safety, engineering, healthcare, and emergency service organizations.
The model posits that accidents are not caused by a single major shortcoming but are the result of multiple factors and the cumulative effects of several errors occurring simultaneously. It likens an organization's defences against failure to slices of Swiss cheese with holes of varying sizes and positions. Each slice represents a safety-critical system, and the holes represent weaknesses in individual parts of the system. When the holes in each slice align, it creates a "trajectory of accident opportunity," allowing a hazard to pass through and leading to a failure.
In the context of aviation, the Swiss Cheese Model considers various factors such as the company, technical staff, air traffic controllers, pilots, the pilot's personal life and physical health, decisions made by authorities, rules, and regulations. By examining these factors collectively, the model helps identify the root causes of incidents and accidents.
For example, let's consider the case of Lion Air Flight 610, which crashed on October 29, 2018. The Swiss Cheese Model can be applied to this incident by identifying multiple defences that should have prevented the accident:
- Flight crew response
- Sensor reliability
- Flight crew training
- Sensor fault information
- Adequate repair of components
- Correct maintenance
- Understanding of aircraft fault history
- Crew resource management
However, despite these defences, the accident occurred due to cumulative failures, including a faulty sensor repair process, poor maintenance procedures, and inadequate training.
In summary, the Swiss Cheese Model emphasizes the importance of multiple factors and defences in preventing accidents. By diversifying the layers of defence and addressing weaknesses, organizations can mitigate risks and improve safety.
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Human errors and aviation accidents
Human error is a significant factor in aviation accidents. Pilots, air traffic controllers, and maintenance staff are the three parties most commonly responsible for these errors. The Swiss Cheese Model, developed by Professor James Reason in 1990, is a widely accepted framework for understanding the causes of aviation accidents. It posits that accidents are not the result of a single failure but rather the cumulative effect of multiple errors and breaches in safety defences. These errors can occur at various levels, from individual mistakes to organisational failures.
Pilots and flight crew members play a crucial role in aviation safety. They make numerous decisions and perform a multitude of actions while operating an aircraft. Mistakes by pilots can be classified as tactical errors, which are based on decision-making, or operational errors, resulting from inadequate training. For example, a pilot may make a tactical error in deciding to take off with wing icing, leading to a crash. Additionally, flight crew members can commit in-flight errors that endanger passengers' safety.
Air traffic controllers are responsible for monitoring and regulating air traffic, directing flight paths, and maintaining safe distances between aircraft. Their work is critical in preventing collisions. However, errors in instruction or decision-making by air traffic controllers can have severe consequences. Staff shortages and long working hours can contribute to weakened decision-making abilities, increasing the risk of accidents.
Maintenance staff are responsible for ensuring the proper functioning of aircraft systems. Incorrect or inadequate maintenance can lead to equipment malfunctions and hazardous flying conditions. Poor maintenance practices, faulty repair processes, and inadequate oversight can all contribute to accidents. For instance, the Lion Air Flight 610 crash in 2018 was attributed to multiple factors, including a faulty sensor repair process and poor maintenance practices.
The Swiss Cheese Model helps identify the interrelations between real-time unsafe acts (active failures) and underlying conditions (latent failures). Active failures are typically made by front-line personnel and have immediate consequences, such as equipment operators, maintenance technicians, and pilots. Latent failures are organisational factors that predispose active failures and can include uncertainties in roles, inadequate oversight, and poor maintenance practices. By addressing latent failures, organisations can effectively prevent accidents and reduce the probability of repeat incidents.
In conclusion, human errors in aviation accidents can have severe consequences. By understanding the complex interplay of factors contributing to accidents, as outlined in the Swiss Cheese Model, aviation authorities can develop robust systems to mitigate risks and enhance safety. This includes addressing individual mistakes, improving training, and implementing organisational changes to create diverse layers of defence against potential hazards.
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Accident investigation and prevention
The Swiss Cheese Model likens an organisation's defences against failure to slices of Swiss cheese with holes of varying sizes and positions. These holes represent weaknesses in different parts of the system. When the holes in the slices align, they create a "trajectory of accident opportunity", allowing a hazard to pass through all defences and lead to a failure. This alignment of holes across multiple defences is known as the cumulative act effect.
The model identifies two types of failures: active failures and latent failures. Active failures are the immediate, direct causes of an accident, often associated with front-line personnel such as pilots, maintenance technicians, and ground support equipment operators. Latent failures are organisational or systemic weaknesses that predispose the system to active failures. They can remain dormant for extended periods until specific conditions trigger them, influencing multiple potential errors. Addressing latent failures is crucial for effective accident prevention, as their presence increases the likelihood of repeat or similar accidents.
To prevent accidents, it is essential to diversify the layers of defence and address weaknesses in each layer. This includes ensuring high-quality training for pilots, implementing robust maintenance practices, closely regulating companies to prevent risky strategies, and considering the impact of organisational culture and policies on safety. By strengthening each layer of defence, the likelihood of a hazard passing through all defences is significantly reduced.
Additionally, the Swiss Cheese Model encourages a comprehensive investigation approach. When examining an accident, it is important to collectively consider various factors, including the company, technical staff, air traffic controllers, pilots, regulatory authorities, and underlying reasons. By adopting this model, investigators can identify the contributing factors and develop strategies to enhance the overall safety of aviation operations.
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Frequently asked questions
The Swiss Cheese Model is a model of accident causation that views accidents as the result of interrelations between real-time unsafe acts by front-line operators and latent conditions. It likens human systems to multiple slices of Swiss cheese, with holes of varying sizes and positions, stacked side by side. The risk of a threat is mitigated by different types of defences layered behind each other.
Active failures are unsafe acts that can be directly linked to an accident, such as a navigation error. Latent failures are aspects of an organisation that predispose active failures, such as uncertainties in roles and responsibilities.
The Lion Air Flight 610 crash on October 29, 2018, is an incident that has been analysed using the Swiss Cheese Model. The defences that should have kept 189 people safe were breached by a faulty sensor repair process, poor maintenance, and possibly inadequate training for the captain and first officer.
A near-miss incident involving Malaysia Airlines at Brisbane Airport in 2018 was a Swiss Cheese Incident. Pitot tubes on the aircraft were covered, but the pilots were able to fight through a barrage of warnings and checklists to land the aircraft safely.
