FAST : Function Analysis System Technique

by jalal mjadli

As I wrote in Introduction to methodology, the FAST method or the Function Analysis System Technique, is a method used by the engineer to transform the product services functions to technical functions. The method proposes an interrogative approach to find solution by finding responses to the famous questions «What?When?and How?». In the present article, I’ll try to explain the concept of FAST.


It is  an other functional anlysis method that helps to describe and to interpret complex systems. It starts by a principal function that will be decomposed to component functions, that can be also decomposed to elementary functions. The analysis go from the More General (MG) to the More Detailed (MD). It adapts an interrogative approach:

  • From MG to MD : it helps to find the way to construct the solution. (How?)
  • From MD to MG : it helps to justify the choice used to construct the solution. (Why?)

Graphical construction

The method has a graphical representation. To represent a function we use a rectangle containing a verb describing the function. The flow of information is an arrow, it can be :

  • Input arrow to describe data or constraint
  • Output arrow to give results of the function (data or constraint for an other eventual function).

An arrow can be unique or combined with other arrows by the logical operators OR and And. The following picture illustrates the principle :

Like the FAST method, we can applicate this example to analysis many systems : Drink dispenser, Public Phone…

Form more details, we can release a FAST digram for any elementary function. It helped to give rise to other methods and it was implemented by different software. FAST is a practical method for professionals and also engineering students to understand the working methods.


© All rights are reserved to the author. Any use of this article is permitted in the context of teaching and non-profit activity.

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