Definition
A model of accident causation in which an organization's defenses against failure are pictured as a series of barriers, each represented as a slice of Swiss cheese. The holes in each slice represent weaknesses or latent failures in that defense. An accident occurs when the holes in successive slices momentarily line up, allowing a hazard to pass through every barrier and result in harm.
Plain English
A way of showing how accidents happen. Each safety layer has small weak spots, like holes in a slice of cheese. Most of the time the layers catch problems. But once in a while the holes line up, the problem slips through every layer, and an accident occurs.
Context Anchor
Seen in aviation safety training, preflight risk discussions, and accident reviews.
Derivation
Named after the appearance of Swiss Emmental cheese, which has visible holes. The model was developed by British psychologist James Reason in the 1990s and has become a standard way of explaining accidents in aviation, medicine, and other safety-critical fields.
Why Pilots Care
It shows why a single small mistake rarely causes an accident, but a chain of small gaps can let a hazard through.
Grounding Statement
Picture several safety nets in a row; the flight becomes unsafe when the gaps in those nets line up at the same time.
Intuition Check
Do not read the Swiss Cheese Model as saying one hole caused the accident. The point is that several weaknesses lined up, and each one failed to stop the problem.
Example Sentence 1
The accident report used the Swiss Cheese Model to show how a fatigued crew, a missed checklist item, and a worn-out indicator light combined to allow the takeoff to begin with the flaps incorrectly set.
Example Sentence 2
Using the Swiss Cheese Model, the safety officer added an extra cross-check to close one of the common gaps in the preflight procedure.