What Is Failure Mode Effects and Criticality Analysis?

FMECA is an approach to risk evaluation that can be done from the bottom up (Hardware) or from the top down (Functional). Inductive or data-driven analysis it links the following elements in a failure chain: Failure Mode, Effect of Failure, and Causes/Mechanisms. These elements are similar to the 5 why technique used in root cause analysis (RCA). The Failure Mode or Technical Failure Description is created by translating the Experience of the User/Customer into the Effect of Failure. The technical failure definition answers the question “Why” by introducing the causes that lead to the failure mode. Each failure mode is assigned a probability and each cause an assigned failure rate. Probability of occurrence will be assigned if data are not available. The FMECA’s probability is based on the source documents used to collect failure data. The FMECA, unlike 5 Why is done before any failure occurs. FMECA measures risk by criticality, which is a combination of severity and probabilities. This allows for action to be taken and reduces the likelihood of failure.

FMECA (Failure Mode and Effects Analysis) and FMEA (FMEA ) are related tools. Each tool aims to identify failure modes that may cause a product or process to fail. FMEA is qualitative and explores “what-if scenarios”, whereas FMECA incorporates a quantitative input based on a known failure rate. Military Handbook 217 (or equivalent) is a good source of such data.

FMECA is divided into two parts:

  1. Create the FMEA
  2. Criticality Analysis

The intersection of severity and probability rankings is measured as criticality. The results are displayed in four main criticality zones. The Criticality of a product or process is used to identify design flaws. FMECA Criticality is available in two quantitative and one qualitative options.

  1. Quantitative
    • Mode Criticality = Item Unreliability x Mode Ratio x Probability (Life) x Time.
    • Item Criticality = Summation of Mode Criticalities
  2. Qualitative
    • Comparing failure modes is possible with a Criticality Matrix. This matrix identifies severity along the horizontal axis and qualitatively determines occurrence along the vertical axis.
    • Note: Quality One suggests a matrix of qualitative criticality for the Quality One Three-Path Model. The vertical axis represents severity, and the horizontal axis shows occurrence. It is sometimes used in place of the Risk Priority Number.

Why Perform FMECA?

The purpose of Failure Mode, Effects, and Criticality Analysis is to improve knowledge of risk in order to prevent failure. FMECA offers tangible benefits in three categories:

Design and Development Benefits

  • Reliability is increased
  • Better quality
  • Safety margins are higher
  • Re-design and reduced development time

Operational Benefits

  • More Effective Control Plan
  • Testing and Verification Requirements Improved
  • Preventive and predictive maintenance optimized
  • Analyse reliability growth during product development
  • Reduced waste and non-value-added operations (lean Operations and Manufacturing)

Cost Benefits

  • Recognize failure modes early (when it is less expensive to fix them)
  • Reduce warranty costs
  • Customer satisfaction increases sales