What Is Failure Mode And Effect Analysis (FMEA)?

Failure Mode and Effect Analysis (FMEA) is a structured, bottom-up reliability method used to identify every way a system or process could fail, determine the effect of each failure on system performance and safety, and prioritize corrective actions based on the risk each failure mode poses. The analysis works by examining individual components or process steps, enumerating their potential failure modes, tracing the consequences of each mode through the system hierarchy, and rating each mode on three dimensions: severity (how serious the effect would be), occurrence (how likely the failure is), and detection (how likely the failure would be caught before reaching the end user). The product of these three ratings yields a Risk Priority Number (RPN) that guides where engineering effort should be directed first.

FMEA was developed by the U.S. military in the 1940s and formally documented in MIL-P-1629 in 1949, later revised as MIL-STD-1629A in 1980. The methodology spread into commercial aerospace, automotive, semiconductor, and consumer product industries, where it became embedded in quality management and design verification processes.

Procedure and Worksheet Structure

An FMEA is conducted against a defined functional block diagram or process flow, working systematically through every item. For each item, the analyst identifies: the item's function, each failure mode (how the item could fail to perform that function), the local effect on the item itself, the effect on the next higher assembly, and the end effect on the system as a whole. Current detection controls, such as inspection steps or self-test routines, are also documented. IEC 60812, the international standard for FMEA and FMECA procedure, specifies the worksheet format, rating scale definitions, and documentation requirements that provide consistency across organizations and programs.

The RPN is computed for each failure mode. High-RPN items are candidates for corrective action, which may include design changes to eliminate the failure mechanism, redundancy to limit the effect of the failure, or added detection controls to catch the failure before it reaches the customer. After corrective actions are implemented, the RPN is recalculated to confirm that the risk has been reduced.

Design FMEA and Process FMEA

Two primary forms of the analysis address different phases and targets. Design FMEA (DFMEA) is conducted on a product design, examining component failure modes and their effects on product function and customer safety. Process FMEA (PFMEA) is conducted on a manufacturing or assembly process, examining process step failures and their effects on product quality characteristics. The SAE standard J1739, widely used in the automotive industry, provides detailed guidance for both DFMEA and PFMEA, including rating scales tailored to automotive safety and quality requirements. Six Sigma programs incorporate PFMEA into the Control phase of DMAIC projects to document and sustain process improvements.

Thermal stress and electrical stress are frequently identified as leading causes of high-probability failure modes in electronic assemblies. Environmental Stress Screening (ESS) programs use DFMEA outputs to select the stress types and durations most likely to precipitate the failure modes identified as highest-risk during design analysis.

Integration with Other Reliability Tools

FMEA is rarely used in isolation. Physics of failure analysis, which models the physical mechanisms driving degradation, provides evidence-based occurrence ratings that replace engineering estimates with quantitative predictions. Failure Reporting Analysis and Corrective Action Systems (FRACAS) feed field failure data back into the FMEA, updating occurrence ratings based on observed in-service failure frequencies and identifying failure modes that were missed or underrated during design. Fault tree analysis works top-down from an undesired event to identify combinations of failure modes that together produce a system-level consequence, complementing the bottom-up perspective of FMEA.

NIST reliability engineering statistics provide the quantitative methods used to estimate failure mode probability from test data and field returns, grounding RPN occurrence ratings in measured rather than assumed values.

Applications

FMEA has applications across a wide range of industries and product types, including:

• Automotive powertrain, chassis, and active safety system design review
• Aerospace and defense system qualification under MIL-STD-1629A
• Medical device design verification and FDA 510(k) submission support
• Semiconductor process control and manufacturing defect reduction
• Nuclear power plant instrumentation and control system safety analysis