Glossary
Diagnostics and Prognostics Terms Related to Integrated Systems Diagnostics Design
These terms are derived from DoD, Academic and Industrial definitions, and have been enhanced to include today’s requirements and processes based on the ISDD Process
Availability, Inherent (AI) – The ratio of operational “up time” to “down time” measured as MTBF over MTBF + MTTR. AI is based on the capability of the design to perform reliably (MTBF) and, in case of failure, the time required to be returned to the operational state (MTTR) with no other factors considered.
Availability, Operational (AO) - The ratio of operational “up time” to “down time” measured as MTBF over MTBF + MTTR + MLDT. Where AI is the inherent design capability, AO reflects the ability to return a failed item to the operational state in the actual support environment. The Mean Logistics Delay time (MLDT) is any maintenance delay due to Logistics factors such as availability of spare parts, maintenance personnel, maintenance scheduling, etc. It is important to understand the impact of AO when referring to this in a specification. A 95% AI is readily achievable through the ISDD process but a 95% AO is not probable due to Logistics delays.
Business Case Analysis (BCA) - The fundamental process to analyze Operational and Support design and strategy decisions. A BCA provides a best-value analysis that considers not only cost, but other quantifiable and non-quantifiable factors supporting an investment decision. This can include, but is not limited to, performance, diagnosability, produceability, reliability, maintainability, and supportability enhancements. BCA is of value to the contractor based on profit margin, and to the customer based on acquisition cost and Life Cycle Cost.
Can Not Duplicate (CND) - The inability to replicate field failures during lower level maintenance assessment. From collected field analyses, CND failures can make up more than 85% of all observed field failures in avionics and account for more than 90% of all maintenance costs. These statistics can be attributed to a limited understanding of root cause failure characteristics of complex systems, inappropriate means of diagnosing the condition of the system, and the inability to duplicate the field conditions in the lower level test environment.
Condition Monitoring – The process of monitoring a parameter of condition in machinery, such that a significant change is indicative of a developing failure. Condition monitoring is being investigated for use with electronic equipment.
Condition-Based Maintenance (CBM) – A methodology that attempts to maintain the correct equipment at the right time based on using real-time data to prioritize and optimize maintenance resources and act only when a maintenance action has been determined through abnormal parametric measurement.
Condition-Based Maintenance Plus (CBM+) – A methodology that expands upon the basic concepts of CBM while attempting to encompass other technologies, processes, and procedures that enable improved maintenance and logistics practices. CBM+ is being redefined through the advancements of Integrated Systems Diagnostics Design (ISDD).
Critical Failures – All failures that that may impact safety or severity of the failure consequence, or will cause the system to perform to a standard less than what is required of it for the following typical conditions:
- Probability of Loss of Mission / Operation
- Probability of Loss of Vehicle / platform / operating system
- Probability of Loss of Life
The ISDD process provides the best design mix of operational redundancy and prognostics.
Deferred Maintenance – A maintenance action on a detected, non critical, failure that can be postponed for corrective action at a later time and at a lower level of maintenance.
Degraded Mode – An operational decision based on completing a mission or operation with a performance less than necessary to complete all aspects of the mission or operation. Degraded modes need to be defined during the diagnostics analysis to support operational planning decisions.
Design Influence – The key value of ISDD to provide proactive diagnostic design decisions based on BCA, and Operational and Support Requirements.
Embedded Diagnostics – The portion of the system's diagnostic capability that is an integral part of the Operational or Support System. This is in comparison to External or Special Test Equipment. The ISDD process provides the means for intelligent trade studies that result in the optimal balance between Embedded and external diagnostics.
Failure – The loss of ability of a system, device or process to perform a required function. This is the manifestation of a fault that leads to an operational failure. The ISDD process identifies faults that can lead to an operational failure and provides the design knowledge to mitigate an operational failure.
Failure Mode – The characteristic manner in which a failure occurs. Within a failure mode diagnostic model, failure modes represent specific ways in which a system, device or process can fail and the effects of this failure are identified for each higher level of assembly up to the system level.
Failure Modes and Effects Analysis (FMEA) – An inductive, bottom-up method of analyzing the system effects of individual failure modes.
Failure Modes and Effects Criticality Analysis (FMECA) – A FMEA that also includes criticality calculations for each failure mode and effect.
Fault Detection Probability (% FD) – The probability measurement of the ability to detect a fault when it occurs.
Fault Isolation Probability (% FI) – The probability measurement of the ability to isolate a detected fault to a given fault group size for a maintenance action.
Health Management (HM) – The capability of monitoring real-time sensors to determine the health and performance of a system, subsystem, device or process. The Health Management System is comprised on a test executive and a reasoning system and may or may not be hosted on the system being managed.
Health Monitoring –An obsolete term related to older systems and non proactive systems where sensor data is collected and stored for later use or measured to determine the health of a system. No embedded interaction is provided to maintain the system’s operational capability.
Informed Maintenance (IM) –A Logistics system that is based on diagnostic information from the proactive ISDD process to intelligently interpret the diagnostic results from the operational system. This provides smart troubleshooting for the maintainer as well as effective maintenance planning and reduced skill level requirements.
Interactive Electronic Technical Manual (IETM) – A publication system that provides information and instructional knowledge to a user through electronic interactive media. The typical IETM speciation today requires S1000D compliance. S1000D requires interaction between knowledge databases and, in the case of a class 2 S1000D IETM, interaction between the IETM and the system / equipment being operated and maintained (related to the old definition of Class 5 IETM). S1000D also requires reuse of data to eliminated data redevelopment. The ISDD process provides for this reuse of data and provides diagnostics test strategies, developed during the design phase, to be imported to an IETM authoring system to meet S1000D compliance.
Integrated System Diagnostic Design (ISDD) – The process of developing diagnostics capabilities for production test, operational health management and life cycle maintenance support. This process relies on a standardized diagnostics analysis capability that can provide integration of all levels of the system diagnostics design, the dissemination of understood requirements, and the integration of design disciplines such as Diagnostics Engineering, Reliability, Maintainability, Logistics Engineering, Test Engineering, Safety, Production Engineering, and others depending on the individual organizational structures. This process also requires accountability of the diagnostics design at all levels of development where the diagnostics capabilities are tested through approved Validation and Verification procedures.
Life Cycle Cost (LCC) – The total cost of acquisition, operation, maintenance, support of an item throughout its useful life, including the cost of disposal. In the past, LCC was specifies as the cost of Operations and Support. Today is looked at as the total cost of ownership, from acquisition through disposal.
Logistics Support Analysis (LSA) – The iterative process of identifying support requirements for a new system, especially in the early stages of system design. The main goals of LSA are to ensure that the system will perform as intended and to influence the design for supportability and affordability. Traditionally the LSA is performed too late in the design process to have any design influence. The ISDD process requires an interaction with the LAS early in the design phase to provide proactive design influence for Supportability.
Loss Of Life (LOL)- The measurement of probability of a failure causing loss of life and is specified as a level 5 criticality in the FMECA.
Loss OF Mission (LOM) - The measurement of probability of a failure causing loss of mission or operation and is specified as a level 3 criticality in the FMECA.
Loss Of Vehicle (LOV) - The measurement of probability of a failure causing loss of vehicle, platform or equipment and is specified as a level 4 criticality in the FMECA.
Maintainability -The ease with which maintenance can be performed on a hardware or software system or component to correct faults, improve performance. It is important for initial maintainability studies to be performed early in the design process to influence the design.
Mean Time to Repair (MTTR) – The reliability weighted mean of repair times for an operational end item This includes test time, access time, fault isolation time, remove and replace or repair time, checkout time, and access secure time.
Mission Critical – Any operational function that, if failed, will degrade or eliminate the possibility of the mission or operation being completed as planned.
No Fault Found (NFF) –The event that results from a failure or fault being detected or reported during operations that cannot be verified at the lower level of maintenance. See Cannot Duplicate (CND) for similar definition.
Physics of Failure Analysis (POF) – A term for identifying and understanding the physical processes and mechanisms of failure.
Predictive Maintenance (PM) – Also defined as Planned, Scheduled, or Preventative Maintenance, is the techniques that help determine the condition of in-service equipment in order to predict when maintenance should be performed in order to prevent its occurrence. PM is employed to increase mission reliability, at the expense of availability and maintenance costs. PM should be minimized but there are instances where it is appropriate and needs to selected based on trade studies. These studies should be performed using a simulation analysis based on diagnostics and maintenance action attributes, including costs.
Proactive Design – The process of integrating all elements of design influence as defined in ISDD, to provide a system or equipment that meets operational and support requirements. An effective proactive design with provide a product with high Availability, low cost, and high mission / operations success.
Prognostic Accuracy or Confidence Level – The accuracy in terms of difference between the future forecast of performance or condition and the actual future value achieved expressed as +/- an amount or as a percentage of the forecast. It may also be applied to the accuracy of the predicted time to failure, time to a given performance degradation point or percentage of remaining useful life, etc.
Prognostic Analysis - The engineering practice associated with evaluating the prognostic capabilities or requirements of a system, device or process. This process in today’s technology is more related to Physics of Failure (CBM) the Heuristics trend analysis (RCM).
Prognostic Engineering – the discipline, body of knowledge, procedures, computation programs, and other resources, which supports Prognostics development and implementation.
Prognostic Features – Measures (or Figures of Merit) derived from data or information that are used by a given prognostic technique.
Prognostic Horizon – The maximum time or related parameter (such as number of missions, etc.) for which a given Prognostic Technique will achieve a set accuracy or confidence level. For example, technique “A” may achieve a 90% prognostic accuracy with a horizon of 200 operating hours, or Prognostic Technique “B” may achieve a 75% prognostic accuracy with a prognostic horizon of 3 missions.
Prognostic Information – Information derived from data and / or other sources used directly or indirectly as a basis for prognostics.
Prognostic Model – A model of a component or system that allows the introduction of faults and degradation to develop or test prognostic techniques.
Prognostic Technology – The body of underlying science and mathematics, which supports Prognostic Engineering.
Prognostics – A “forecast of future performance and / or condition”.
Prognostics Health Management (PHM) – The discipline that links studies of failure mechanisms to system lifecycle management. A process to Health Management that includes as its base, the capability of diagnostics with selected prognostics as defined in the ISDD process.
Remaining Useful Life (RUL) – Represents the expected time the group, or a member of the group, is expected to survive after the analysis date.
- The care and servicing by personnel for the purpose of maintaining equipment and facilities in satisfactory operating condition by providing for systematic inspection, detection, and correction of incipient failures either before they occur or before they develop into major defects.
- Those based upon a model of the application and the responses of the model to introduced faults or degradation.
- Those based upon direct sensor measurement, feature and feature vector development, and analysis and prediction based upon these parameters.
- Those based upon statistical treatment of data or information.
- A combination of any or all of the preceding three.
- Applicability or robustness of the prognostic technique or system – how many other applications can the technique be applied to with commensurate accuracy, reliability and horizon attributes.
Trade Study – A structured process which compares options using predefined performance criteria to result in the selection of the best design that satisfies all requirements. Trade Studies are highly iterative and are used during all development phases to ensure that all factors which might impact a function or requirement are considered.