This article will explain a very famous model describing how accidents in aviation happen. The swiss cheese model or Reason’s model.

 

Where does this model come from?

The model is based on the research from Dante Orlandella and James T. Reason of the University of Manchester. It is also known as “cumulative act effect”. The basic idea behind is, that in a system or organization, “single-lapses” will not destroy the whole.

Swiss cheese model in detail

The basic concept is, that in a (more or less) complex system different layers are existing – our cheese slices.

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These slices unfortunately are not perfect. They have holes (imperfections) which allow for penetration. Each slice forms a different layer in our system. Generally these layers are:

• Organizational layer
• Supervision / training layer
• Layer of (unsafe) precondition
• The layer of unsafe acting

Of course, these layers depend on the organization / system, nevertheless these are the basic ones related to aviation.

For example:

Organizational layer

Flying club or (if you are a professional pilot) the airline itself applies cost-cutting strategies in order to save money and lower the operating costs of the fleet. Some strategies might infringe or at least negatively influence aviational safety.

Supervision / training layer

Indeed a very important layer in flying. Superior training is key to safe operation of aircraft. Have you been in a hurry during your initial training sometimes? Are you sure that your training was sufficient?

Layer of (unsafe) precondition

Now we come down to the current flight. Stress, fatigue, lack in concentration – nobody can be at the best performance level all the time. But maybe we should ask ourselfes: “Do I really need to fly today?” or “How safe am I?” – You can easily check yourself with this little guidance.

The layer of unsafe acting

All before mentioned layers / slices are latent conditions. This means that the are more or less subcontiously existing. The last layer here is an active one. An active condition that is (hopefully) obvious – the handling of the error / failure itself. Maybe it is a wrongly handled rough running engine. Or a bad action applied by the pilot like flying into adverse weather. There are certain dangerous attitudes that might impose a great risk.

 

Each slice of cheese imposes a risk to the complete system. But the worst could happen if there is real hazard (like a rough running engine) and the alignment of the layers is in a way that this hazard can pass all the way trough – then the worst could happen:

• Unproper maintenance due to cost cutting -> unseen technical issues
• Insufficiently trained pilot -> does not know how to handle this situation
• Weather is bad already -> ground is maybe not visible to conduct a precautionary landing
• Pilots’ attitude is resignatory -> the situation is too much, possibility of CFIT

 

Conclusion

Accidents in aviation rarely happen due to a single event, it usually is a chain of errors. Some of them are obvious, some of them not.

To prevent the worst from happening, the only possibility is to work on all levels to close the gaps and subsequently reduce the risk of fatal errors.