Fault Tree Analysis (FTA) – Definition & Examples

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What is a Fault Tree Analysis (FTA)?

Fault Tree Analysis is a diagrammatical representation of different causes of system failure. Whenever an undesirable event occurs in an organization, you need to analyze its origin with the help of Fault Tree Analysis. You can check the system's reliability while stepping across a series of events in a logical manner. Generally, it is a failure probability function determined by the togetherness of various components as well as the system's architecture logic.

Fault Tree Analysis

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Why is Fault Tree Analysis Important?

A risk-based path depicted through Fault Tree Analysis is the primary concern for finding the root cause of the unwanted event. Moreover, it also helps the problem solver to look for events leading to the root cause of the base-level event.


Purpose of Fault Tree Analysis

  • The main goal is to determine potential causes in system failure after the happening of an undesirable event.
  • The probability of top events can also be evaluated using statistical or analytical methods.
  • The calculations involved serve the primary purpose of maintainable and reliable information such as failure rate, failure probability, and repair rate.


Benefits of Fault Tree Analysis

  • A visual representational record of a system is determined to show the logical relationships between causes and events that lead to system failure.
  • The analysis helps others to understand the results and pinpoint the weaknesses quickly.
  • At the same time, it also lays the foundation for any further evaluation and analysis.
  • When you make upgrades or changes to the system, with Fault Tree Analysis, you already have steps for possible changes and effects.
  • A Fault Tree diagram can also be used to maintain procedures and design quality tests.


Fault Tree Analysis VS. Event Tree Analysis

Here are some points of difference between Fault Tree Analysis and Event Tree Analysis.



When to use Fault Tree Analysis?

As discussed previously, a Fault Tree Analysis helps in science-related subjects, namely aerospace, pharmaceutical analysis, software engineering, chemical processes, energy, designing fuel power for aircraft, and designing diagnostic manuals. However, you can use it in engineering where system failures have enormous consequences like aeronautics or nuclear power and software development industry to debug complex systems.

Well, every industry needs Fault Tree Analysis for:

  • Defining the system
  • Defining the top-level faults
  • Identifying top-level fault causes
  • Identifying the next level of events
  • Identifying root causes
  • Adding event probabilities
  • Analyzing fault tree
  • Documentation of FTA


Symbols of Fault Tree Analysis

For drawing a fault tree diagram, you can use logic gates and symbols along with specific Fault Tree Analysis shapes.

The first failure event is a circle. The house like symbol describes the external event. This event is either expected to occur or average. An undeveloped event gets indicated with a symbol that doesn't need any further investigation or breakdown or analysis because of a lack of information.

A restriction on an event gets represented through a conditioning event. A Boolean relationship describes different outcomes.

Gate Symbols

  • AND Gate

If all conditions of input meet, this event occurs.

  • OR Gate

This event occurs when at least one of the event happens.

  • Priority AND Gate

It is a restricted scenario where the event occurs only after the fulfillment of certain conditions.

  • Exclusive OR Gate

It’s opposite to the Priority AND Gate. The event occurs after one condition meets, and not all.

  • Inhibit Gate

This event will occur after happening of all events described in a conditional event.

Fault Tree Analysis symbols



It includes the following shapes.

  • External Event

A house symbol is generally accepted to occur.

  • Basic/Primary Event

A circle depicts an error or failure in an element or system component.

  • Undeveloped Event

This event requires no more investigation due to a lack of information resources.

  • Conditioning Event

It is a restriction, especially on the logic gate.

  • Intermediate Event

In this event, there are detailed descriptions of events, and they are above a primary event.

Fault Tree Analysis symbols


Fault Tree Analysis Diagram Shapes

Here are some standard logos that indicate the Fault Tree Analysis shapes.

Fault Tree Analysis symbols


Fault Tree Analysis Examples

You can better understand with the help of these Fault Tree Analysis examples.

Example 1:  Aircraft Crash

In the first Fault Tree Analysis example, you will see the causes of an aircraft crash. It can be a navigation fault or low aircraft speed. Furthermore, several reasons for aircraft’s low speed develop as the primary motor closed ahead of time, or rocket booster separates ahead of time, etc.

Fault Tree Analysis example


Example 2:  Employee Turnover

Employee Turnover is much helpful in finding out the potential causes of employee turnover and is divided into three main categories, such as employee entry, an employee leaving, and employee change. Below you can see the complete analysis of employee turnover.

Fault Tree Analysis example


Example 3:  Scaffolding Fall

You can conveniently analyze fall from scaffolding through Fault Tree Analysis. There can be two potential causes, such as fall by accident, and safety belt not working. Safety belt not working is further divided into ‘broken by equipment,’ and ‘did not wear a safety belt.’ In this way, ‘Fall by accident’ is also analyzed with this diagram.

Fault Tree Analysis example


How to perform a Fault Tree Analysis?

Performing a Fault Tree Analysis is comfortable with the best online tools, such as EdrawMax Online. The recommended tool is free up to three projects and uses a straightforward interface.

Factors to be considered before making a Fault Tree Analysis diagram:

  • Identify the problem or hazard. You should know for how long, for how much, safety impact, environmental impact, and regulatory impact of it.
  • Then, understand the system to analyze. Here, you can obtain support information, list the potential causes of the problem in the next level, estimate the probability of reasons, and label them with codes.


Now, move on to the steps to create the Fault Tree Analysis Diagram with Edraw Max Online

Step 1:  Open the official website

Firstly, open the official site of Edraw Max Online. You need to sign up with the site for access to free templates and the creation of the project.

EdrawMax online


Step 2: Search Fault Tree Analysis

In this step, you can either search Fault Tree Analysis or click Management from the sidebar. Then, click the Fault Tree Analysis presented in the main interface.

Fault Tree Analysis EdrawMax


Step 3:  Open Fault Tree Analysis Template

Now, you need to open the Fault Tree Analysis template from the following free templates provided in the same window. There are various premium or free options available. With a premium account, you can create unlimited projects. On the other hand, the free version allows you to create only three projects at hand.

Fault Tree Analysis EdrawMax


Step 4:  Draw Fault Tree Analysis diagram

Open any of the free templates available and start creating your customized diagram from it. You can choose from various symbols and shapes provided. It is quite simple to create an FTA diagram with EdrawMax Online.

Fault Tree Analysis EdrawMax


Limitations of Fault Tree Analysis

Well, Fault Tree Analysis also suffers from several limitations.

  • You need to foresee and evaluate first the undesired event. Thus, you have to anticipate all contributing factors to the cause.
  • The effort sometimes may prove to be very expensive and time-consuming unless you equip certain skills to analyze the FTA yourself.
  • If the reader doesn’t possess skills, then Fault Tree Analysis may not be desirable to use.


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