A fishbone diagram, also known as an Ishikawa diagram or a cause-and-effect diagram, was developed by Kaoru Ishikawa in the 1960s. It is a visual representation of the causes of a problem or failure. The diagram is structured as a fish skeleton, with the problem or event being represented by the head of the fish, and the causes of the problem branching off the bones of the fish.
Fishbone diagrams are used in maintenance to identify the root cause of a problem. They can also be used to identify patterns and trends, which can help prevent similar problems from occurring in the future. In this article, we will define what a fishbone diagram is and share a use-case example of how a fishbone diagram can be used.
What is a fishbone diagram?
Fishbone diagrams are a visual tool that shows all the possible reasons a problem or event may have occurred, as well as their source. It can be useful if the maintenance team is coming up short when troubleshooting an issue. Every possible cause is categorized by its source. Causes are then reduced again and again until you can isolate the root cause of a problem or outcome.
How do fishbone diagrams work?
A fishbone diagram helps maintenance teamstrace the steps that could have led up to a problem, like a piece of equipment breaking down. Take an aircraft, for example. Let’s say the ground crew engineer discovers that a compressor is malfunctioning. There are many possible causes of the malfunction, but by using a fishbone diagram, the crew can break the problem down into main categories. In this instance, you could isolate the issue in the following steps:
- Personal: List out anyone who may have been performing maintenance or repairs on the aircraft
- Machinery: Define and outline the technology
- Materials: List the raw parts used to construct the aircraft
- Measurements: Detail the inspection and steps taken
- Environment: Detail the climate, geographical, and other factors relating to the environment
- Methods: List the processes
In steps 1 and 2, you could break it down even further and into more detail. You know that some compressor parts were just 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. For example:
- New parts may have been installed improperly
- A part is malfunctioning or was not inspected properly
- A technician installed the compressor incorrectly
- Some tools may be left inside the compressor housing
- There 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 or drone strike
- The turbine was inspected and compressor wear was noted
- The inventory for the aircraft parts and labor lists all of the pieces and staff who were active around the aircraft in a 48-hour span
The information that you have linked off of the first stem of ideas brings you closer to discovering the root cause of the problem. You have identified the main possibilities and now you can expand each possible cause by choosing the most probable outcome. This is what that might look like in our example:
The mechanic installed a part incorrectly which caused a malfunction. This caused the turbine to become damaged during a flight. This is the primary cause (also known as the main cause) of the failure.
Now that this hypothesis has been created, inspections can focus on certain traits, which means less time searching for a problem and less overall downtime for the aircraft. Even better, if this sort of problem is documented, there can be preventive and predictive maintenance making sure similar malfunctions are avoided in the future.
Other tools in your arsenal along with fishbone diagrams
There are also methods of troubleshooting, like root cause analysis (RCA) and the 5 whys methodology, which helps increase the chances of isolating the root cause of an issue. A fishbone diagram is a 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 on-site or you could introduce more regular inspections to prevent further failures and minimize downtime. A fishbone diagram allows a simple but logical process of elimination which leads to faster problem resolution, ensuring your business reduces downtime and increases productivity.