SMS Pro Aviation Safety Software Blog 4 Airlines & Airports

3 Methods for Root Cause Analysis in SMS Programs

Posted by Tyler Britton on Jul 10, 2017 5:55:00 AM

How to Conduct Root Cause Analysis

Methods for root cause analysisRoot cause analysis for one aviation safety manager is not root cause analysis for another safety manager. There is no standard definition or process for root cause analysis. This lack of standardization is not a negative thing, as it gives aviation service providers flexibility to create a process that best fits them. In anticipation of this, oversight agencies like the FAA or ICAO provide little guidance on how to do it.

It’s less important to “define” root cause analysis than to understand how you can use a method to meet root cause analysis goals. Root cause analysis is performed by adopting a method, such as:

  • 5 whys analysis;
  • Bowtie analysis; or
  • Fishbone diagrams.

Either of these methods will be used to:

  • Understand the base mechanisms contributing to a safety event;
  • Establish precursors to dangerous conditions (i.e., hazards, risk events, etc.); and
  • Discover underlying causes contributing to safety/exposure in the SMS program.

Here is a more in-depth look at three methods for root cause analysis.

1 – How to Create Fishbone Diagrams

Fishbone diagrams, also known as cause and effect diagrams, derive their name from the fish-like appearance of a completed diagram. Fishbone diagrams are also known as cause and effect diagrams and Ishikawa diagrams.

Fishbone diagram example for root cause analysisThese diagrams have:

  • A “head,” which is your hazard/risk event;
  • 4-6 “fins” which are the categories that you are using to organize root causes of a safety event (e.g., Man, Machine, Mission, Management, etc.);
  • Fins can be a predefined model, such as 5-M or SHELL, or a custom model created by you;
  • Each fin will have multiple “branches”; and
  • Each branch may or may not have sub-branches.

Filling out these diagrams simply involves looking at the safety issue from the perspective of each fin (category), and establishing the relevant factors (branches). Next, for each branch, establish the reasons (sub-branches) that the branch exists. These sub-branches are usually your root causes. See the above example picture to see what this looks like.

The benefits of using fishbone diagrams are:

  • Very comprehensive;
  • Identifies all major and minor root causes;
  • Provides visual reference; and
  • Organizes root causes by type of cause.

The cons of fishbone diagrams are:

  • No justification for findings; and
  • Can be hard to distinguish major and minor root causes.

2 – How to Perform 5 Whys Analysis

5 whys analysis is the most common method used for root cause analysis. Some of the reasons this method is ubiquitous in aviation SMS programs are:

  • Quick;
  • Simple; and
  • Provides lineage of events.

Unlike some of the other methods however,

  • No visual product; and
  • Somewhat narrow in comparison to other root cause analysis methods.

Performing 5 whys analysis is easy to do. It involves starting at your hazardous condition/risk event, and then asking “Why did this happen?” You will then establish the preceding event/reason that lead to the hazardous condition. Next, you will ask, “And why did this preceding event happen?” Once again, you will establish the next event back.

You will repeat this process until you arrive at the root cause. Usually you will ask "why?" about 5 times, give or take a couple. You know you have arrived at the root cause when there is no real answer to “why?” In other words, when your answer “just because,” you have arrived at the root cause.

3 – Using Bowtie Analysis for Root Cause Analysis

Bowtie analysis is traditionally considered a comprehensive analysis solution, as it establishes everything from root causes to final consequences. Because bowtie analysis is so thorough, it can be time consuming and abstruse. However, there is no reason organizations can’t use only the “left side” of the bowtie to establish a timeline of all contributing events from root causes to the hazardous condition.

Performing bowtie analysis for root causes is somewhat similar to 5 whys analysis:

  • Establish hazardous condition;
  • Ask “Why did this happen?” and list the preceding event(s);
  • For each preceding event ask “And why did this happen?” – once again, list the preceding events; and
  • Like the 5 whys, when your answer is “just because,” you have arrived at a root cause.

Unlike the 5 whys, bowtie analysis:

  • Has a visual product to reference;
  • Establishes all major (but not minor) root causes; and
  • Shows flow of events from all major root causes to hazardous condition.

However, reasons you might use 5 whys analysis instead of bowtie are:

  • Bowtie analysis is much more time consuming (better suited for higher risk issues); and
  • Bowtie analysis has a learning curve.

Final thought: Creating Custom Root Cause Analysis Method

It’s also possible to create a custom root cause analysis method that meets your organization’s specific needs. For example, you might create:

  • A special type of investigation geared towards root causes; or
  • A new type of model (i.e., similar to bowtie, fishbone, etc.).

It’s not so important which method you use. What matters is how well your root cause analysis meets the goals of root causes analysis.

For a similar method of analysis, see this guide to SMS Shortfall Analysis. 

Shortfall Analysis Identify SMS Failures

Topics: 3-Safety Assurance

Site content provided by Northwest Data Solutions is meant for informational purposes only. Opinions presented here are not provided by any civil aviation authority or standards body.



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