Failure modes effects and diagnostic analysis (FMEDA)

What is FMEDA?

Failure modes effects and diagnostic analysis (FMEDA) is a systematic methodology to identify potential failure modes within a system, component, or process to analyze the effects. It extends the traditional failure modes and effects analysis (FMEA) (opens in new tab). Compared to FMEA, FMEDA goes beyond just diagnostic capabilities and examines how and why failures occur alongside the effectiveness of the diagnostic mechanisms in detecting these failures.

It's important to understand what each component of FMEDA refers to. Failure modes refer to the various ways in which a system, component, or process can fail. For example, wear and tear on a mechanical part due to prolonged use leads to a breakdown. Effects analysis involves examining the outcome of each identified failure mode and understanding the impact on system performance. For example, if a critical component fails, the system might lose important functions, like braking in a vehicle. Diagnostic analysis evaluates the effectiveness of existing diagnostic measures in detecting and addressing failure modes. For example, sensors that detect abnormal conditions, like temperature spikes, trigger alarms, or automatic shutdowns.

How is FMEDA used?

FMEDA is employed to assess the reliability and safety of products, especially in high-risk industries. It is primarily used to:

1. Identify failure modes: Recognize potential ways a component or system can fail.
2. Analyze effects: Understand the consequences of these failures on the overall system.
3. Evaluate diagnostics: Examine the existing diagnostic measures to detect and address failures.
4. Quantify metrics: Calculate reliability metrics such as failure in time (FIT) rates, diagnostic coverage (DC), and safe failure fraction (SFF).

Who uses FMEDA?

Professionals in high-reliability and safety-critical industries widely use FMEDA. This often includes engineers, product developers, and system designers across industries like:

• Aerospace: To ensure the safety and reliability of aircraft components and systems.
• Automotive: For evaluating the safety and reliability of aircraft components and systems.
• Medical: To ensure that medical equipment operates reliably without causing harm to patients.
• Industrial automation: In the design and maintenance of automated manufacturing systems.

Steps to conduct FMEDA

1. Define the scope: Determine the system, component, or process to be analyzed.
2. Assemble a team: Gather experts from various disciplines (engineering, product, safety, and quality control).
3. Identify failure modes: List all potential failure modes for each component.
4. Analyze effects: Assess the impact of each failure mode on the system.
5. Evaluate diagnostic coverage: Determine the effectiveness of the existing diagnostic mechanism in detecting each failure mode.
6. Quantify reliability metrics: Calculate failure in time (FIT) rates, diagnostic coverage (DC), and safe failure fraction (SFF).
7. Document findings: Record all identified failure modes, their effects, diagnostic coverage, and calculated metrics.
8. Review and revise: Continuously review and update the FMEDA process as new information or technologies become available.

What are the standards and guidelines of FMEDA?

Several industry standards and guidelines guide FMEDA to ensure consistency, accuracy, and compliance with safety and reliability requirements. Here are some of the key standards and guidelines:

1. IEC 61508: Functional safety of electrical/electronic/programmable electronic safety-related systems. IEC 61508 is a fundamental standard for functional safety. It provides guidelines for the entire lifecycle of safety-related systems, from design to decommissioning. Specifically, it includes:
   • Safety integrity levels (SILs): This concept defines four levels of safety integrity, with associated probability ranges for failure.
   • FMEDA requirements: Specifies how FMEDA should be used to assess the reliability and diagnostic coverage of safety-related components and systems.
   • Quantitative analysis: Emphasizes the need for quantitative analysis of failure rates, diagnostic coverage, and safe failure fraction.
2. ISO 26262: Road vehicles–functional safety. ISO 26262 is the automotive industry standard for the functional safety of electrical and electronic vehicle systems. Key aspects related to FMEDA include:
   • Hazard analysis and risk assessment (HARA): helps determine the automotive safety integrity levels (ASILs) that guide FMEDA.
   • Product development at the system and hardware level: This specification specifies the use of FMEDA to evaluate hardware components for compliance with ASIL requirements.
   • Fault metrics: This requires calculating fault metrics such as FIT rates, diagnostic coverage, and latent fault metrics.
3. ISO 13849: Safety of machinery–safety-related parts of control systems. ISO 13849 focuses on the safety of machinery control systems. Relevant FMEDA guidelines include:
   • Performance level (PL) determination: FMEDA determines the performance level of safety-related parts.
   • Risk assessment: Involves FMEDA as part of the overall risk assessment process.
   • Diagnostic coverage and MTTFd: This section emphasizes the need to calculate the mean time to dangerous failure (MTTFd) and diagnostic coverage.
4. IEC 62061: Safety of machinery–functional safety of electrical, electronic, and programmable electronic control systems. IEC 62061 is another machinery safety standard, complementing ISO 13849. It includes:
   • Safety requirements specification: Utilizes FMEDA to develop and verify safety requirements.
   • SIL assignment: FMEDA is required to ensure components and systems meet the assigned SIL.
   • Diagnostic measures: Focuses on implementing and verifying diagnostic measures through FMEDA.

Advantages and disadvantages of FMEDA

As with most methodologies, there are always advantages and challenges; below is a table to illustrate both regarding FMEDA: