February 26, 2020


Sofema Aviation Services considers best practice methodology to deliver effective Root Cause Analysis (RCA).

Using Both 5 Why & Fishbone as a tool together to understand Cause and Effect and to determine the various contributing causes as well as ultimately the Root Causes provides for a better outcome in combination than using each individually.

Introduction to 5 Why’s – Cause & Effect Why!

A technique which involves repetition of the question why? Each question forms the basis of the next question. The “5” in the name derives from an empirical observation on the number of iterations typically required to resolve the problem.

5 Why’s can be used throughout the business either to assess a real issue or to analyse a potential issue (What If Scenarios). Fundamentally it is related to the structure of the questioning process which we follow to understand both contributing factors and ultimately the Root Causes.

Why 5 Why’s?

Simply it is an arbitrary value selected to take the user some way on the journey to the “Ultimate Root” of the problem.

The disadvantage of 5 Why’s

A downside of 5 Why is that it does not address the branches of multiple root causes in the most effective way. It is therefore not the best tool for performing RCA however it is ideal for brainstorming and for supporting an understanding of the elements within a chosen branch.

What is the Fishbone Technique?

A fishbone diagram also called a cause and effect diagram or Ishikawa diagram is a visualization tool for categorizing the potential causes of a problem in order to identify its root causes.

It’s is typically employed by both individuals and teams to brainstorm and logically organise potential causes.

Performing with Fishbone:

– Write down in detail the issue or problem statement;

– Consider as a question and start with understanding the why, focus brainstorming (ideally with others);

– Traditional ‘fishbone’ major factors include:

    • People
    • Equipment
    • Method
    • Process
    • Materials
    • Information
    • Environment

Boning Out

Now make the bones of your fish and add these as headings for each bone.

Disadvantage of Fishbone for our Root Cause Analysis?

The fishbone diagram typically has four or Six different groupings. There are many variations, however, the purpose of the diagram is to list anything that may have an influence in respect of each topic.

The fishbone is a tool for brainstorming ideas in different areas, It is not best suited to prove a cause-and-effect relationship. Therefore the use of a fishbone is more appropriate for brainstorming rather than analysis.

Combine Fishbone with 5 Why

Process Advantages – Helps to summarise potential high-level causes & stimulates the identification of deeper potential causes.

Fishbone can be used when a more detailed analysis is required for a specific problem. Drill down further when used together with 5 Why’s.

Delivery of Combined Process:

    • Construct the Fishbone as above
    • Drill down into the issues – use 5 Why for technique support
    • Group into relevant subcategories
    • Keep going until you have a diagram showing all the possible causes.
    • Look for causes that appear more than once.
    • Determine if additional investigation is required or we have reached the root cause.
    • Consider the optimum solutions and propose to the business


Sofema Aviation Services and SofemaOnline provide EASA Compliant Regulatory & Vocational Training including Quality & Safety Assurance and Root Cause Analysis Techniques. Please see the websites or email office@sassofia.com or online@sassofia.com


aviation, Aviation System Root Cause Analysis, Fishbone Techniques, RCA, Root Cause Analysis