Glossary
Availability
The probability that a system is operational when called upon to perform its function. The numerical value of availability is expressed as a probability from 0 to 1. Availability calculations take into account both the failures and the repairs of the system.
Bill of Materials (BOM)
Fixed-format ASCII files where each piece of information appears between certain columns.
Presents the list of used parts.
Criticality
Mean number of the system failures during a mission phase because of a block or its failure mode. The criticality value is used to rank failure modes when performing a FMECA. Criticality for a severity, counts only the system failures of this severity because of a block or its failure mode .
Criticality Matrix
Each element of this matrix represents the number of system failures of a certain severity within a certain probability interval of occurrence.
Duty Cycle
Used when computing failure rates based on active and dormant settings. The duty cycle is equal to the percentage of total time the item or system is in the active environment.
Fault / Event Tree Analysis
A process designed to determine the probability and rate of an event (particularly – a failure) based on cause-effect relationships.
Failure Mode and Effect Analysis (FMEA)
An inductive, bottoms-up method of analyzing system design and performance. At the core of a FMEA is the determination of the effects of various types of failures on a system. Various standards such as SAE J1739, AIAG Potential Failure Mode and Effects Analysis, as well as documents from Ford, Chrysler, and GM, provide instructions and formats on performing FMEAs.
Failure Mode, Effects and Criticality Analysis (FMECA)
An inductive, bottoms-up method of analyzing system design and performance. At the core of a FMECA is the determination of the effects of various types of failures on a system. A criticality factor, assigned to each failure mode, allows ranking the most severe failure modes and the ones most likely to occur. The analyst may then target these failure modes in order to reduce their probability of occurrence. MIL-STD-1629 provides instructions and formats for performing FMECAs.
Failure Rate
The number of failures experienced or expected for a device divided by the total equipment operating time. For constant failure rate items, i.e. exponentially distributed failures, the failure rate is the numerical inverse of the mean time between failures (MTBF).
Life Cycle Cost (LCC)
A method of analyzing the cost of a piece of equipment over its entire life, including development costs, production costs, operation costs, support costs, and disposal costs.
LSAR files
(Also known as Logistics Support Analysis Records.) Text files that conform to MIL-STD-1388 2B. They contain reliability and maintenance data for a system and its modifications.
Maintainability Prediction
The measure of the ability of an item to be retained in or restored to a specified condition when skilled personnel perform the maintenance. Among maintainability parameters are: mean time to repair (MTTR) and Maximal Corrective Maintenance Time (MCT max).
Mean Time Between Failures (MTBF)
The mean time expected between failures for repairable or replaceable items, typically measured in hours. MTBF is meant to be the mean over an infinite period of time MTBF is the inverse of the failure rate. If failure rate is in failures/million hours, MTBF = 1,000,000 / Failure.
Mean Time to Failure (MTTF)
The mean time expected for the first failure of an item. It is meant to be the mean time over an infinite period of time for fully repairable items and for replaceable ones with new spares. MTTF is equal to MTBF.
Mean Time to Repair (MTTR)
The Mean time required to make an item operable on the repair site.
Measures of Reliability
When performing a reliability prediction analysis, there are several calculated values that provide measures of reliability. These values include failure rate, mean time between failures (MTBF), reliability and availability.
Parts Libraries
Data on commercial and military parts, including diodes, transistors, integrated circuits, resistors, capacitors, and non-electronic parts.
Reliability
The ability of an item to perform a required function under stated conditions for a stated period of time without failures. The numerical value of reliability is expressed as a probability from 0 to 1 and is also sometimes known as the probability of mission success. Reliability is the probability, assuming the system was operating at time zero that it continues to operate until time t.
Reliability Analysis
A method of analyzing a system design evaluating reliability-related issues. The goal is to improve the field reliability of the system.
Reliability Block Diagram (RBD)
A visual representation of a system composed with sub-blocks, RBD may contain redundancy in its elements. Redundancy is used for mission critical functions where a single-point failure is not acceptable and reliability needs to be improved. Generally represented in a graphical manner. Results of RBD calculation may include reliability, availability, failure rate, and MTBF.
Reliability Calculations
Performed in order to quantify the reliability of a piece of hardware or software prior to and during development and production.
Reliability Centered Maintenance (RCM)
Methodology used to define a maintenance program while having reliability or safety as a goal to the decision making process. Originally developed by the aviation industry and known as MSG-3 (Maintenance Steering Group), Reliability Centered Maintenance or RCM has since been adopted by many different industries.
Reliability Prediction
A primary component of reliability analysis is referred to as the failure rate, or the number of failures expected during a certain period of time. Calculation of equipment failure rate, and the related MTBF (Mean Time Between Failures), is the basis of performing a reliability prediction analysis.
Relification
A new word in English which was invented by Mr. Yizhak Bot, President and CTO of BQR, which means Reliability Verification. Exactly as Qualification is Quality Verification.
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