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Pros and Cons of Fishbone Diagrams in Aviation SMS Programs

Posted by Tyler Britton on Feb 8, 2017 6:06:00 AM

What is a Fishbone Diagram for Aviation Safety Programs

Pros and cons of fishbone diagrams in aviation SMS programsFishbone diagrams are a lesser known but very effective risk management tool in aviation SMS programs. Fishbone diagrams get their name because of their fish like appearance, with several fins and a head. Each “fin” or “branch” of a fishbone diagram describes a different element of the safety issue, such as “Man” and “Machine.” The head describes the Top Event (also known as Risk Event, the point at which safety control is lost).

Fishbone diagrams are also known as Cause and Effect diagrams, or Ishikawa diagrams. In operational environments they are usually used to:

  • Establish causes and effects that lead to safety issues;
  • Understand the relationship between causes and effects; and
  • Explore root causes of a safety issue.

Unlike other risk management tools, such as a Risk Matrix, the fish bone diagram does not include any subjective elements like likelihood or severity. It simply looks at the facts.

Also, fishbone diagrams are only concerned with the events that precede the Top Event, and not with events that come after.

How to Create Fishbone Diagrams

We discuss how to create fishbone diagrams in greater detail in a previous article. However, the basic steps work like this:

  1. Choose model framework to create the “fins”, such as the SHELL model or 5-M model (or create your own);
  2. Establish the Top Event – point at which safety control is lost – and add it to the “head” portion of the diagram;
  3. Establish primary causes in each fin and create smaller branches for each of those causes; and
  4. For each primary cause, establish root cause by asking “why did this happen.”

Once finished, there a are a couple of things to note:

  • Root causes may appear in more than one fin because of overlap;
  • Some fins may have very few items; and
  • Bolding the most important root causes will be helpful for future reference.

Creating fishbone diagrams is actually surprisingly easy with a bit of practice. 

Benefits of Fishbone Diagrams in Aviation SMS Programs

There are some strong benefits of fishbone diagrams in aviation risk management.  

  • Comprehensive root cause analysis;
  • See how causes work together to produce safety issues;
  • Understand how effects of causes materialize in operational environment;
  • Objective look at how safety issues originate and develop;
  • Over time will develop a state of the art hazard register;
  • Fishbone diagrams are a part of proactive risk management because you are identifying underlying causes and events before safety control is lost;
  • Understand contributing factors;
  • Can easily develop aviation leading indicators based on findings; and
  • Develop superior, comprehensive risk controls.

Moreover, unlike other risk management tools that provide many “comprehensive” benefits, fishbone diagrams can be completed in a relatively short amount of time. This makes fishbone diagrams accessible and useful for nearly all safety issues.

We might contrast this to the Bowtie, which also provides “comprehensive” benefits, but takes much more time to complete; thus, it is usually only used on medium/high risk issues.

Cons of Fishbone Diagrams

Despite the numerous “comprehensive” benefits of fishbone diagrams, there are some rather big drawbacks as well. These drawbacks mainly center on the fact that fishbone diagrams are only look at the first half of a safety issue.

Remember, anything that happens after the Top Event is not analyzed in fishbone diagrams. The consequences of this are that:

  • Fishbone diagrams should be coupled with a second risk management tool that captures events that happen after safety control is lost;
  • They are not used for reactive risk management activities (an important part of any SMS program);
  • They are (generally) not used for predictive risk management activities;
  • They do not capture failures in human behavior or risk controls in reaction to negative events.

We might contrast this with Bowtie analysis again, where Bowtie analysis is comprehensive of events before and after safety control is lost – it covers everything from root causes to final impacts.

Scenarios When To Use Fishbone Diagrams

As said, fishbone diagrams can be done quickly enough that they are useful in any situation. In general however, fishbone diagrams are used when:

  • Performing root cause analysis;
  • Reviewing breakdowns in risk controls;
  • Analyzing contributing factors; and
  • Understanding role of Human Factors in safety issue.

All of the above scenarios are perfect candidates for situations in which to use fishbone diagrams.


For more information about improving other risk management operations, see these workflows:

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