Project problems? Use a fault tree analysis to get back on track

Project problems? Use a fault tree analysis to get back on track

We all know that sinking feeling when we realize our project hasn’t gone to plan. But rather than wasting time beating yourself up, embrace the opportunity to work out what went wrong and improve. Doing this shows you’re both taking accountability – which is a sign of great leadership – and you’re doing everything you can to get back on track, which shows resilience.

But what if you’re not sure exactly what went wrong? This is where a fault tree analysis (FTA) comes in handy.

What is a fault tree analysis?

It’s a diagram that helps you determine the cause of failure. An FTA gives you a visual representation of a process from start to finish, including all of the relationships or between events. Seeing all of this information in a top-level diagram helps you logically pinpoint weaknesses and identify the causes of failure.

But it’s more than a reactive tool: it also helps you proactively look at a project and identify areas where things might go wrong by logically guiding you through a series of events.

How can a fault tree analysis help you?

  • It helps you locate errors, then prioritize tasks that go toward fixing the issue(s).
  • It helps inform future projects. For example, if you are repeating a task, you can use your past fault tree analysis to identify and avoid problems. You can also use it as a foundation to conduct further analysis for similar projects.
  • You can use your diagram to help design quality and maintenance procedures.
  • Presenting information in a diagram means everyone can understand the relationships between different events at-a-glance.
  • It also means you have a visual record of your analysis, which you, your team, and stakeholders can refer to at a later date.

Who needs a fault tree analysis?

FTAs are most useful for anyone whose work involves a series of steps and relationships, especially in industries where failure can have a big impact, such as aeronautics, petrochemicals, finance, or nuclear power. It’s also useful for helping software engineers debug systems.

Fault tree diagram symbols explained

Fault tree diagram symbols fall into two categories: events and gates. You’ll find a description of the different symbols, as well as their meanings below.

Fault Tree Analysis SymbolsCreated in Cacoo


  • A Basic Event shows the failure event in a process and requires no additional analysis.
  • An External Event shows something that is normally expected to occur.
  • An Undeveloped Event is used to indicate a situation where information is not available or determined to be unimportant.
  • A Conditioning Event indicates a restriction that’s applied to a logic gate.
  • An Intermediate Event shows additional event information.
  • Transfer In/Out is denoted by a triangle and indicates a transfer to a related fault tree.


  • An Or Gate should be used if one or more of the input events occur.
  • The And Gate refers to an event that occurs only if all the input conditions are met.
  • The Exclusive Or Gate refers to an event that occurs only if one — and only one — of the input conditions are met.
  • The Priority And Gate is for an event that occurs if all of the input events occur in a specific order.
  • The Inhibit Gate denotes an event that will only occur if all input events take place, as well as whatever is described in the conditional event.

How to make a fault tree analysis diagram

1. First, you need to define your system and work out what constitutes failure. This is especially important in software or engineering, where one element could fail, but the rest of the system could potentially continue operating. There should be one top-level failure per fault tree.

2. Next, add inputs, which may or could potentially contribute to the top-level fault. This is where logic gate symbols come in: use them to organize which causes lead to the failure, and which require multiple events before causing failure.
Tip: use diagramming software to create your fault tree quickly and easily with the help of a pre-made template.

3. Now analyze the fault tree diagram to work out the actual or potential root cause(s) of the top-level failure. Identify likely events that lead to failure, or that initiate paths or patterns that lead to issues. Then work out ways to resolve or mitigate these paths. You may want to combine this stage with a cause and effect diagram to help you determine each cause.

4. Finally, define and launch your plan. Alongside your basic symbols, you can note down the probability of each event contributing to the top-level failure, and then add actionable items or create a risk management plan.

Final thoughts

You can create a fault tree analysis with a wide range of tools, but by far the easiest option is a dedicated online diagramming tool. Creating your diagram in the cloud means your team always has the latest version at their fingertips. It also means you can access real-time updates and feedback whenever someone adds a comment, actions an item, or edits your diagram. This means you can spend less time sending out update emails and more time collaborating with your team.

Georgina Guthrie Georgina is a displaced Brit currently working in France as a freelance copywriter. Before moving to sunnier climates, she worked as a B2B agency writer in Bristol, England, which is also where she was born. In her spare time, she enjoys old films and cooking (badly).