Reason's model, commonly referred to as the Swiss cheese model, was based on Reason's approach that all organizations should work together to ensure a safe and efficient operation. From the pilot's perspective, in order to maintain a safe flight operation, all human and mechanical elements must co-operate effectively in the system. In Reason's model, the holes represent weakness or failure. These holes will not lead to accident directly, because of the existence of defense layers. However, once all the holes line up, an accident will occur.
There are four layers in this model: organizational influences, unsafe supervision, precondition and unsafe acts.