FMEDA: Quantitative Hardware Safety Analysis
Build the worksheet behind the ISO 26262-5 hardware metrics row by row: failure rates, failure-mode shares, fault classes and diagnostic coverage, then the SPFM, LFM and PMHF they produce.
- Chapters
- 10
- Chapters
- Figures
- 21
- Figures
- End-to-end worked example
- 1
- End-to-end worked example
Quick answers
- What is FMEDA in ISO 26262?
- FMEDA (Failure Modes, Effects and Diagnostic Analysis) is the quantitative hardware safety analysis behind the metrics of ISO 26262-5. It extends FMEA with a failure rate for every part, split across its failure modes, and a diagnostic coverage for every safety mechanism that detects those modes. Each failure mode is classified against the safety goal in scope, and the results roll up into three numbers: SPFM and LFM for the architecture and the PMHF for random hardware failures. Together they show whether the hardware design meets the targets for its ASIL.
- What is the difference between FMEA and FMEDA?
- FMEA is qualitative: it asks how parts can fail and what that causes, and ranks actions. FMEDA is quantitative and coverage-aware: it assigns each failure mode a failure rate, classifies it into a fault class, credits the safety mechanisms that detect it, and sums everything into the hardware metrics. An FMEA tells you where to worry; an FMEDA tells you whether the design numerically meets the ISO 26262-5 targets. It is maintained from the hardware concept through verification.
Why it pays for itself
Build the worksheet row by row
Scope the analysis to a safety goal, give each row a documented failure rate and failure-mode share, and see how the rows add up to SPFM, LFM and PMHF on an illustrative circuit.
Classify every fault correctly
Trace each failure mode to the safety goal and sort it into safe, single-point, residual or multiple-point faults, the step where many FMEDAs quietly go wrong.
Defend diagnostic coverage claims
Map safety mechanisms to the rows they actually cover, account for overlapping mechanisms and latent faults, and back each claimed coverage with a reason a reviewer accepts.
What you’ll be able to do
Scope and structure a worksheet
Set up rows per safety goal with a sensible level of detail and clear column ownership.
Justify rates and shares
Document where each failure rate and failure-mode share comes from and how the mission profile affects it.
Classify faults correctly
Sort every row into safe, single-point, residual or multiple-point faults against the goal in scope.
Defend coverage claims
Tie each claimed coverage to a mechanism, a row and evidence, including latent-fault tests.
Review a supplier FMEDA
Read rows critically and spot the patterns that make metrics indefensible.
Chapter by chapter
- 01
What an FMEDA Does
See how a parts list becomes classified failure rates and metrics, what the worksheet adds to an FMEA, and who fills which column.
- Parts to classified rates
- Five column groups
- Who fills which column
- 02
Scoping the Worksheet
Scope the analysis to one safety goal at a time and decide which parts become rows and at what level of detail.
- One safety goal at a time
- Which parts become rows
- Level of detail
- 03
Failure Rates per Row
Give each row a documented failure rate, adjust it for the mission profile, and handle permanent and transient faults.
- One source per part family
- Mission profile factor
- Permanent and transient rows
- 04
Failure Modes & Shares
Split a part failure rate across its failure modes and decide what to do when no distribution data exists.
- Rate per failure mode
- Where shares come from
- Current-sense shunt split
- 05
Classifying Each Row
Trace each failure mode to the safety goal and sort it into the right fault class, including rows that belong to safety mechanisms.
- Tracing the effect
- Two questions per row
- Safety mechanism rows
- 06
Coverage in the Worksheet
Map safety mechanisms to rows, split each row by coverage, and make the claimed coverage defensible for both residual and latent faults.
- Mapping mechanisms to rows
- Defensible DC numbers
- Start-up and periodic tests
- 07
From Rows to Results
Sum the columns into the hardware metrics, see what passes to the PMHF, and find the rows that dominate the result.
- Summing the columns
- What goes to PMHF
- Levers and side effects
- 08
Worked Example
Build a complete illustrative worksheet for a brake-by-wire pedal travel sensing path and iterate the design once.
- Pedal travel sensing circuit
- One row step by step
- One design iteration
- 09
The Worksheet in Practice
Plan build order and handoffs, integrate a supplier IC analysis, keep the worksheet alive, and relate it to the FMEDA simulator.
- Build order and handoffs
- Supplier IC analysis
- Keeping it alive
- 10
Reviewing an FMEDA
Read rows like a reviewer, separate myths from reality, and spot red flags at worksheet level.
- Reading a row
- Myths and reality
- Worksheet red flags
Read all 10 chapters with Expert.
Start with a free account: the complete Functional Safety Concept guide and 5 practice exams a month, then upgrade when you need this guide.
Expert plan pricingNot just text: the visual toolkit
Five column groups
The structure of the FMEDA worksheet at a glance.
The failure-rate receipt
How one part rate travels from its reference value to the value used in the row.
Effect ladder
Worksheet rows traced from the part pin to the safety goal.
How one row splits
A failure mode divided by coverage into the fault classes.
Contributor Pareto
Which rows dominate the result of the worked example.
Pedal travel sensing for brake-by-wire
An illustrative pedal travel sensing path with two sensor ICs on inverse slopes is analyzed end to end, then revised once to show how a design change moves the result.
- The item, its safety goal and the sensing circuit
- Building one worksheet row step by step
- The complete example worksheet
- Totals and the verdict against the goal
- One design iteration and what it changes
Unlock in course
Who this guide is for
- Hardware safety engineers building their first FMEDA from a bill of materials
- Reliability engineers moving from qualitative FMEA into quantitative ISO 26262-5 analysis
- Reviewers auditing a supplier FMEDA for optimistic coverage or under-counted latent faults
- Engineers whose SPFM or PMHF misses its target and who need to find out why
Frequently Asked Questions
Common questions about FMEDA: Quantitative Hardware Safety Analysis
Start the course today
A free account unlocks one full concept guide, 3 work product templates, 1 guided process, the Markov and RBD simulators, and 5 practice exams per month. The Pro and Expert plans unlock more of the 93-guide library. No credit card required.
Continue with
Where this topic leads next.
- HardwareHardware Element EvaluationStudy ISO 26262-8:2018 Clause 13: element classes, evidence, evaluation scope and integration responsibilities.
- HardwareSoft Errors & Transient FaultsA cosmic ray hits a memory cell and your ASIL D function computes with a wrong value. This concept walks from the physics of radiation-induced bit flips through single event effects, ECC and hardened design, all the way to Part 11 quantification.
- SoftwareSoftware Architectural & Unit DesignLearn architecture patterns for fault isolation, testability, and diagnostic coverage in safety-critical software. Covers modularity, design-by-contract, complexity metrics, and structural coverage requirements per ASIL.