Reliability Engineering
Concept
Topic overview
Quick facts
- Definition of Reliability Engineering in functional safety
- Reliability Engineering in depth
- The case for Reliability Engineering
- Reliability Engineering in practice
- Where teams get Reliability Engineering wrong
- Reliability Engineering and its standards
- Industries where Reliability Engineering applies
- Ask our team about Reliability Engineering
- Terms related to Reliability Engineering
Reliability engineering asks how often things fail and works to make the answer smaller: it predicts failure rates from component data and environmental stresses, expresses them as MTBF or MTTF, characterizes life behavior (early failures, useful life, wear-out, the classic bathtub curve), accelerates discovery of weaknesses through techniques like HALT, screens production escapes with HASS and burn-in, and runs field failure reporting and corrective action loops (FRACAS) so real-world data continuously corrects the predictions.
Its outputs are business quantities: warranty cost, spares provisioning, availability, maintenance intervals.
The relationship to safety is intimate but not identity, and the distinction matters: reliable is not safe.
Safety cares about the direction of failure, not just its frequency, a system that fails rarely but dangerously is worse than one that fails often but always to a safe state, which is why safety analysis splits every failure rate into safe and dangerous, detected and undetected fractions before using it.
The disciplines can even pull against each other: a hair-trigger safety system maximizes safety integrity while wrecking availability through spurious trips, and operators respond to nuisance trips by bypassing the safety system, converting a reliability problem into a safety one.
Well-run programs therefore engineer the spurious trip rate as deliberately as the dangerous failure rate.
Reliability engineering supplies the raw material for the quantitative side of functional safety, the component failure rates feeding and calculations come from reliability databases and reliability testing, and it is the R and part of the M in , where reliability and maintainability together determine the availability that rail contracts bind with penalties.
The case for Reliability Engineering
For product leaders the distinction pays twice. Commercially, reliability is its own profit line, warranty, uptime guarantees, spares, brand, and deserves engineering investment independent of any safety mandate.
On safety programs, understanding that MTBF does not measure safety prevents two expensive errors: marketing a high MTBF as if it were a safety claim, which assessors and sophisticated customers dismantle, and starving the reliability function that produces the failure-rate data without which the safety calculations cannot be done at all.
Reliability Engineering in practice
Reliability program flow
Reliability engineers produce predictions during design from recognized databases and manufacturer data adjusted to the real environment, run accelerated life and robustness testing on prototypes, and operate the field data loop after release, feeding corrective action and updating the models.
On safety programs they partner with the safety engineer: reliability supplies failure rates and mode distributions, safety classifies them as safe or dangerous for each function, and both disciplines meet in the and the availability model.
Reviewers check the data pedigree (sources, environmental adjustment, sample sizes behind test claims), whether field data actually flows back into the predictions, and whether availability and spurious-trip modeling reflects the operator's real maintenance regime.
Where teams get Reliability Engineering wrong
Reliability Engineering and its standards
In programs run to EN 50126, Reliability Engineering is one of the things the assessor checks first - specification and demonstration of reliability, availability, maintainability and safety for railway applications.
IEC 61508 sets the requirements that Reliability Engineering work has to satisfy: the umbrella functional safety standard defining the safety lifecycle, sil levels, and requirements for electrical, electronic, and programmable systems.
Reliability vs functional safety view of failure
| Aspect | Reliability | Functional safety |
|---|---|---|
| Failures counted | All failures | Dangerous failures only |
| Key metric | MTBF, availability | PFH, PFDavg, MTTFd |
| Goal | Keep it running | Keep it safe, even if stopped |
| A safe shutdown is | A failure (downtime) | A success (safe state) |
Industries where Reliability Engineering applies
Rail & Transit programs lean on Reliability Engineering because the sector covers freight and passenger rail signaling, train control, and transit systems.
Reliability Engineering shapes how industrial machinery teams argue safety - fixed and mobile machinery, packaging lines, and manufacturing equipment.
Ask our team about Reliability Engineering
Ben TwomblyFounder & CEOLeads CSA's functional-safety, certification, and engineering programs for safety-critical products and organizations. His assessor-side background informs practical programs that connect standards, engineering work, and credible evidence.
Jeff Twombly, PEExecutive, Rail SafetyProvides executive and technical leadership for rail-safety programs, assessments, and complex transit-system work. His experience spans safety assurance, transportation-safety leadership, signaling, and independent review.
Tom CyrPrincipal Safety Engineer, IFSPSupports industrial and rail functional-safety programs with safety analysis, requirements, lifecycle planning, and certification-readiness guidance.Terms related to Reliability Engineering
How each connects to Reliability Engineering:
RAMS appears in the same lifecycle work as Reliability Engineering and is usually produced or reviewed alongside it.
FMEDA is the natural next concept after Reliability Engineering; assessors expect teams to connect the two.
Functional Safety appears in the same lifecycle work as Reliability Engineering and is usually produced or reviewed alongside it.
IEC 61508 connects the two: Reliability Engineering and SIL are assessed against the same lifecycle.
Both Reliability Engineering and Safety Function sit under IEC 61508, so evidence for one usually references the other.
Safe Torque Off is governed by IEC 61508 as well, which is why the two show up together in audits.
IEC 61508 connects the two: Reliability Engineering and PFH are assessed against the same lifecycle.
FMEA is governed by IEC 61508 as well, which is why the two show up together in audits.
IEC 61508 connects the two: Reliability Engineering and Fault Tree Analysis are assessed against the same lifecycle.
EN 50126 connects the two: Reliability Engineering and ISA are assessed against the same lifecycle.
CENELEC Rail Standards is governed by EN 50126 as well, which is why the two show up together in audits.
ATO is governed by EN 50126 as well, which is why the two show up together in audits.