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Fishbone Diagrams

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Fishbone Diagrams For Maintenance

Fishbone diagrams (also known as the Cause and Effect diagram) is a brain storming tool that shows the construct of a specific event. It can be useful if the maintenance team is coming up short when troubleshooting an issue. Every possible cause is categorized into a more overall, generic reason. Causes are then reduced again and again until you can isolate the probable outcome or means to an end. Fishbone diagrams inherited their name from the frame like design that resembles a fish skeleton. This is a casual way to assess a situation and outline what the cause of the problem could potentially be.

How do fishbone diagrams work?

The concept behind this casual processing is to allow yourself the opportunity to trace the steps that could have led up to the malfunction or problem. Take an aircraft for example, assume the ground crew engineer discovers that a compressor is malfunctioning. There are many possibilities, but by using fishbone diagrams, you can break the problem down into main categories. In this instance, for example, you could isolate the issue as follows:

  • Personal: Anyone who may have been performing maintenance or repairs on the aircraft
  • Machinery: The technology
  • Materials: The raw parts making the construct of the aircraft
  • Measurements: The inspection
  • Environment: Climate, geographical, other factors relating to “mother Nature”
  • Methods: The process


This is the first step. In step 2, you could break it down even further. You know that some compressor parts had just been replaced, and some new staff were working on the plane recently. You can now expand on the primary categories and see if you can identify the factor that caused the overall effect:

Materials: the raw basic parts

  • New parts may have been installed improperly
  • A part is malfunctioning or was not inspected properly

Personal: anyone working on the aircraft

  • A technician installed the compressor incorrectly
  • Some tools may be left inside the compressor housing
  • Their was something jamming the rotation of the compressors that the mechanic missed
  • The pilot pushed the compressor too far and may have damaged it during the flight


  • Bird strike

Measurements: inspection

  • Turbine was inspected and compressor wear was noted
  • The inventory for the aircrafts parts and labour lists all of the pieces and staff who were active around the aircraft in a 48hr span

The information that you have linked off of the first stem of ideas brings you closer to discovering the cause of the problem. You have identified the main possibilities and now you can expand again even more in depth by choosing the most probable outcome, for example:

The mechanic installed a part incorrectly which caused a malfunction causing the turbine to become damaged during a flight. Now that this hypothesis has been created, the inspection should look for certain traits isolating the entire search reducing the down time of the aircraft. Even better, if this sort of problem is documented, there can be preventative and predictable maintenance making sure malfunctions such as this are avoided in the future.

Another tool in your arsenal

In a previous blog, we introduced the 5 whys method of troubleshooting which is a simple tool to help increase the chances of isolating the root cause of an issue. The fishbone diagram is another handy tool for troubleshooting any mechanical, electrical or operational issue. As demonstrated in the example above, allow yourself to isolate and categorize the potential problems into subcategories making the troubleshooting fluent and efficient.

In the case of the Aircraft example, knowing certain mechanical failures could possibly reoccur, you could store the part onsite or you could introduce more regular inspections to prevent further failures and minimize downtime.  A fishbone diagram allows simple but logical process of elimination which leads to faster problem resolution, ensuring your business reduces down time and increases productivity.

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