To understand the differences between Failure Modes and Effects Analysis (FMEA) and Failure Modes and Criticality Analysis (FMECA), you need to go backwards in time.

Let’s start with a little bit of history. The concept of planning for risk management started back in 1949 when the American military issued a directive to suppliers – MIL STD 1629. This directive was refined and reissued for the benefit of the Aerospace sector as ARP 926.

 

Today when we talk about FMEA and FMECA, in general terms, we consider them to be both the same and interchangeable but actually, there is a difference between the two and the difference can be significant. If we go back to the birth of FMEA, the template that was used was not very sophisticated and ranking severity, occurrence and detection was yet to be instigated. Back in these early days, the criticality element of FMECA was required to allow risk in FMEA to be prioritised. As FMEA templates developed and became more refined, the prioritisation of risk became easier to determine and the use of FMECA became less significant.

So what is the difference? Well, this can best be summarised by asking the question, “You have the FMEA, so now what?”

Well, FMEA only determines risk in broad terms and at times is not very incisive. So, how do I create FMECA? The process steps are outlined as follows:

We can see that Criticality Analysis is conducted post FMEA.

 

FMECA can be conducted based on the following approaches:

Top-Down Approach – System Level / Sub System Level
The top-down approach is mainly used in an early design phase before the whole system structure is decided and the analysis is usually function-oriented. The analysis starts with the main system functions, and how these may fail. Functional failures with significant effects are usually prioritised in the analysis, however, the analysis will not necessarily be complete. The top-down approach may also be used on an existing system to focus on problem areas.

Bottom-Up Approach – Component Level
The bottom-up approach is used when a system concept has been decided. Each component on the lowest level of indenture is studied one-by-one. The analysis is complete once all components are considered.

The Criticality Analysis (CA) can be performed using either a quantitative or a qualitative approach. Availability of part configuration and failure rate data will determine the analysis approach.

 

As a general rule:
• use a Quantitative approach when actual component data is available;
and
• use a Qualitative approach when no actual component data or only generic component data is available.

 

 

 

 

The results of the Criticality Analysis will result in either a defined value (Quantitative), where Failure Mode Criticality (CM) is calculated as:

 

Or, as a matrix (Qualitative):

 

To find out more about FMEA and FMECA and how Industry Forum can support your journey of improvement and achieving zero defects, email us or phone +44 121 717 6600 to talk to our expert practitioners.

A Bit More About Richard
Richard Hammond has over 30 years of auditing and consulting experience within automotive and aerospace sectors. He began his career at Rolls Royce Motors Plc, where he graduated to the role of Maintenance and Installation Engineer, before progressing to his current position as Principal Consultant at Industry Forum via Industrial Robotics and Certification Body Auditing. As a qualified SMMT trainer, Richard delivers the recognised International Automotive Task Force (IATF) ISO/TS16949 Certification Body Auditor training and evaluation. Richard is an approved IATF Witness Auditor and delivers Core Tools training (APQP, PPAP, SPC, MSA, FMEA and Control Plan) into major aerospace and automotive OEMs and tier 1 suppliers.

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