Glossary and FAQ

The reliability-engineering terms used across this wiki, and the questions that come up most.

Glossary

RCM	Reliability-centred maintenance. Task selection by failure consequence, to SAE JA1011.
FMEA / FMECA	Failure mode and effects analysis; FMECA adds criticality ranking.
RPN	Risk priority number, Severity × Occurrence × Detection, 1 to 1000.
Action Priority	The AIAG-VDA 2019 replacement for RPN: High, Medium or Low, weighting severity first.
RBD	Reliability block diagram. System reliability from block logic: series, parallel, k-out-of-n.
RAM	Reliability, availability and maintainability modelling, usually by Monte Carlo simulation.
MTBF / MTTF	Mean time between failures (repairable) / to failure (non-repairable).
MTTR	Mean time to repair. The core maintainability measure.
MTBM / MDT	Mean time between maintenance / mean down time, including logistic and admin delay.
A_i / A_o	Inherent availability (corrective only) / operational availability (all downtime).
Weibull β / η	Shape parameter (failure pattern) and characteristic life (63.2% failed).
B-life	The age by which a stated percentage has failed, for example B10 for 10%.
Hazard rate h(t)	The instantaneous failure rate at age t; rising means wear-out.
Minimal cut set	The smallest set of failures that together cause a fault-tree top event.
P-F interval	The warning window from detectable potential failure P to functional failure F.
ISO 14224	The standard for reliability and maintenance data collection and taxonomy.
SAE JA1011	The standard defining the minimum criteria for a process to be called RCM.
MIL-STD-1629A	The origin standard for FMECA and criticality analysis.
Redundancy	Extra capacity so the system survives a failure: active (parallel) or standby.
GARPI™	Global Asset Reliability and Performance Index: the independent, ISO 55001 and GFMAM-aligned Optimal benchmark of asset-management maturity, a 0 to 100 composite score across eight weighted dimensions and five maturity tiers.

FAQ

Is RCM just more preventive maintenance?	No. RCM often removes calendar tasks, choosing on-condition or a deliberate run-to-failure where that is cheaper and just as safe. It aims the effort, it does not simply add to it.
FMEA or FMECA?	FMECA where you need to rank and prioritise, which is almost always on production assets. FMEA alone is fine for a quick qualitative pass.
Why not just use RPN?	RPN hides risk: different modes share a number and severity can be masked. Action Priority (AIAG-VDA 2019) is the current practice, and it leads with severity.
Which availability should I quote?	Operational availability for what the plant lives, inherent availability for what the design allows. The gap between them is the improvement opportunity.
Do I need sensors to use the Studio?	No. It is design and analysis and starts from the asset register and failure history. It gets sharper as OptimalTREND™ condition data flows back in.
How does it relate to OptimalTREND™?	OptimalAvailability Studio™ decides which failures to manage on condition and sets the intervals; OptimalTREND™ executes that in the predictive domain and feeds the real trends back.

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