<<< Back to Index
This Month's Article >>>

FMEA Corner 
This Month's Theme is Making the FMEA Scope Visible
Next month's theme will be "Ground Rules and Assumptions"

Every month in FMEA Corner, join Carl Carlson, a noted expert in the field of FMEAs and facilitation, as he addresses a different FMEA theme (based on his book Effective FMEAs) and also answers your questions.

Questions and answers are a great way to learn about FMEAs, for both experienced and less experienced FMEA practitioners. Please feel free to ask any question about any aspect of FMEAs. Send your questions to Carl.Carlson@EffectiveFMEAs.com, and your contact information will be kept anonymous. All questions will be answered, even if they are not featured in the FMEA Corner.



scope [skohp, noun]
The Oxford English Dictionary defines "scope" as "the extent of the area or subject matter that something deals with or to which it is relevant."

vis·i·ble [viz-uh-buhl, adjective]
The Oxford English Dictionary defines "visible" as "able to be perceived or noticed easily."

Why is it important to make the FMEA scope visible?

"The soul cannot think without a picture" – Aristotle

As discussed last month, determining the scope of the FMEA is an extremely important step because clearly defined boundaries establish the issues that are to be considered and the approach that the team will take during the analysis.

Making the scope visible ensures that the FMEA team agrees on the precise extent of the FMEA, including interfaces. Elements of the diagram can map to corresponding elements of the FMEA to help ensure that nothing is missed.

The following sections provide a brief introduction to four types of visual depictions that are commonly used to demonstrate the scope of a FMEA. More detailed information, including examples for each type, can be found in Chapter 5 of Effective FMEAs.

FMEA Block Diagram

An FMEA Block diagram (or Boundary diagram) is a visual depiction of the entire system or design to clearly show the boundaries of the FMEA (i.e., what is included and not included), the interfaces between the items and other information that can help to depict the scope of the analysis.

An FMEA Block diagram is recommended as part of the preparation for every System or Design FMEA.

An example of an FMEA Block diagram for a hand brake subsystem of a bicycle is shown next.

FMEA Block diagram

FMEA Interface Matrix

An FMEA interface matrix is a chart with the subsystems and/or components (depending on the scope of the FMEA) on both the vertical and horizontal axes. The chart shows which interfaces must be considered in the analysis and the type of interface.

Used for System and Subsystem FMEAs, the FMEA interface matrix is supplemental to the FMEA Block diagram and is done when the FMEA team wants to ensure that all of the various types of interfaces are included in the analysis, missing none. When it is used, it is a good idea to assign character designations for each interface and map them to the corresponding items or functions in the FMEA, to be sure that all desired interfaces are addressed within the scope of the FMEA.

Parameter Diagram

A Parameter Diagram (or P-Diagram) takes the inputs from a system/customer and relates those inputs to desired outputs of a design that the engineer is creating, while also considering non-controllable outside influences. It is a useful tool in brainstorming and documenting input signals, noise factors, control factors, error states and the ideal response of the system.

A P-Diagram is most useful when the item under analysis is a complex system with many system interactions, operating conditions and design parameters, and the team will benefit from seeing these elements visually.

Process Flow Diagram

A Process Flow Diagram (PFD) is a graphical representation of all of the process operations that result in the manufactured or assembled product, and are within the scope of the Process FMEA project. This is essentially the process hierarchy, including manufacturing and assembly operations, shipping, incoming parts, transporting of materials, storage, conveyors, tool maintenance and labeling, and any other steps of the operations that are within the scope of the Process FMEA.

A PFD is done as part of the preparation for all Process FMEAs. Some practitioners use a Process Flow Diagram Worksheet (or PFD Worksheet) which includes a more detailed description for each process step, and other information, such as the significant product and process characteristics.


An interface is the point or surface where two parts or subsystems meet, and it can take various forms. There are four primary types of interfaces:

Since interfaces can contain up to fifty percent or more of the total failure modes, it is essential that any FMEA carefully consider the interfaces between subsystems and components in addition to the content of the subsystems and components themselves.

!FMEA Tip for Beginners

For System and Design FMEAs, a properly done FMEA Block diagram is recommended, with a visible representation of the different types of interfaces. The other diagrams (Interface Matrix and Parameter Diagram) are optional and depend on specific selection criteria.

For Process FMEAs, a properly done Process Flow Diagram is recommended, visually showing the specific manufacturing and assembly operations that will be analyzed.

!FMEA Tip for Experienced Practitioners

When using P-Diagrams, certain portions of the P-Diagram map to corresponding elements of an FMEA. For example, the "ideal response" of the P-Diagram can provide input to the primary functions of the corresponding System/Design FMEA; the "error states" can provide input to the failure modes of the FMEA, and "control factors" can provide input to key product characteristics of the FMEA.


The following is a rough draft of a fictitious FMEA Block diagram for an all-terrain bicycle. At least four interfaces are missing. Can you identify three of them? [Show/Hide Answer]

FMEA Block diagram

?Something I’ve always wanted to know about FMEAs
The important thing is not to stop questioning. - Albert Einstein

A reader submitted the following question to Carl Carlson. To submit your own question about any aspect of FMEA theory or application, e-mail Carl at Carl.Carlson@EffectiveFMEAs.com.

I will be leading some FMEA work for a new product we are developing. The product is primarily comprised of purchased components for which we are not design responsible. The individual suppliers will be held responsible for the DFMEAs of their respective components, and I am thinking that the FMEAs I will be facilitating internally will be primarily "interface FMEAs" to ensure that component A marries up to component B, etc.

Now for the challenges: In a perfect world, the suppliers themselves would all be involved, but I can guarantee you they won't all be. Suppliers are scattered across the globe. The factories that will ultimately make the product are also scattered (Europe, Asia, USA), which will make the PFMEA work a challenge. Any suggestions on how to manage the supplier FMEAs?

Carl: I agree with you that suppliers should do Design FMEAs for the designs they are responsible for, and Process FMEAs for the manufacturing processes they are responsible for. I also agree with you that your company should perform the system/subsystem FMEAs, including interfaces. I typically like to differentiate critical parts from the rest of the bill of materials. For critical parts, I require suppliers to submit FMEAs to the higher-level company, and review and approve them according to the FMEA quality objectives that are discussed in my book. I also like to involve critical suppliers in the interface discussions on a need-to-know basis.

That's the best approach, in my opinion.

Best Regards,


About the Author

Carl S. CarlsonCarl S. Carlson is a consultant and instructor in the areas of FMEA, reliability program planning and other reliability engineering disciplines. He has 35 years of experience in reliability testing, engineering and management positions, and is currently supporting clients from a wide variety of industries, including clients of HBM Prenscia. Previously, he worked at General Motors, most recently senior manager for the Advanced Reliability Group. His responsibilities included FMEAs for North American operations, developing and implementing advanced reliability methods and managing teams of reliability engineers. Previous to General Motors, he worked as a Research and Development Engineer for Litton Systems, Inertial Navigation Division. Mr. Carlson co-chaired the cross-industry team that developed the commercial FMEA standard (SAE J1739, 2002 version), participated in the development of SAE JA 1000/1 Reliability Program Standard Implementation Guide, served for five years as Vice Chair for the SAE's G-11 Reliability Division and was a four-year member of the Reliability and Maintainability Symposium (RAMS) Advisory Board. He holds a B.S. in Mechanical Engineering from the University of Michigan and completed the 2-course Reliability Engineering sequence from the University of Maryland's Masters in Reliability Engineering program. He is a Senior Member of ASQ and a Certified Reliability Engineer.

Effective FMEAsSelected material for FMEA Corner articles is excerpted from the book Effective FMEAs, published by John Wiley & Sons, ©2012. Information about the book Effective FMEAs, along with useful FMEA aids, links and checklists can be found on www.effectivefmeas.com. Carl Carlson can be reached at carl.carlson@effectivefmeas.com.