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An Introduction to Tools and Techniques
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This table summarises some of the Safety Assessment Tools and Techniques available to the safety assessor. Each of these tools has its own advantages and disadvantages and the extent to which these can be used during various phases of the product lifecycle, and the degree to which they can be applied to safety assessments, vary. For a list of Advantages and Limitations of each, see Appendix A to Aircraft System Safety: Military and Civil Aeronautical Applications.
It is extremely important to note that as the complexity of the tool increases so does the degree of training required for the user and/or the need for an experienced evaluation team to conduct the evaluation. On the plus side, the data derived from the more complex methodologies may be more supportable. Unfortunately, the primary disadvantage of such tools is that "trained subject matter experts" may have limited experience in the actual operational environment and, therefore, their evaluations may not be entirely applicable to the certification process.
To hide this text and give you more room to view the table of tools and techniques, click the "minus" sign symbol at the top right of the container surrounding this introduction.
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Tools and Techniques
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| | Name | Description |
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| Particular Risk Assessment (PRA) | A form of CCA. Technology or circumstance dependant analysis which considers common events or influences that are outside the system(s) concerned (e.g. fire, lighting) which may violate failure independence claims. Some of these risks may also be the subject of specific airworthiness requirements.
PRA examines common events that are external to the systems concerned, but which may violate independence requirements (e.g. uncontained engine rotor failure; fire; bird strike; lightning; HIRF; Human Factors, etc). (e.g. Damage may result in multiple systems failing; Incorrect pilot response could lead hazardous flying condition). Each risk is then examined to assess any simultaneous or cascading effects of each risk. |
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| Petri Net Analysis | Petri Net Analysis is a method to model unique states of a complex system. Petri Nets can be used to model system components, or subsystems at a wide range of abstraction levels; e.g., conceptual, top-down, detail design, or actual implementations of hardware, software, or combinations [Tarrents, 1980] |
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| Physics-of-Failure | This family of approaches differs significantly from the other empirical reliability prediction methodologies and is used primarily at the sub-device level during the design stage. Physics-of-Failure approaches attempt to identify the "weakest link" of a design to ensure that the required equipment life is exceeded by the design. The methodology generally ignores the issue of defects escaping from the manufacturing process and assumes that product reliability is strictly governed by the predicted life of the weakest link. Example models address microcircuit die attach fatigue, bond wire flexure fatigue and die fatigue cracking. The models are very complex and require detailed device geometry information and materials properties. In general, the models are thought to be most useful in the early stages of designing devices (e.g., hybrids) but not at the assembly level when flexibility no longer exists to change device designs. |
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| Pilot Subjective Evaluation (PSE) | Human Factors evaluative tool
Use of the PSE, which has been |
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| PRISM | PRISM is a new technique (release in 2000 based on the Reliability Analysis Centre's databases) which has the ability to model the effects of thermal cycling and dormancy. It provides the ability to update predictions based on test data and addresses factors such as development process robustness. Available as an automated tool (as opposed to a handbook compendium of models like the others), PRISM interfaces directly with RAC's electronic and nonelectronic automated databases and provides an elaborate methodology to assess the quality of the system development process.
It includes a means to include software reliability but is limited by the fact that it does not yet include models for all commonly used devices. The PRISM system reliability model is: ?S = ?IA(?P?IM?E + ?D?G + ?M?IM + ?E?G + ?S?G + ?I?E + ?N + ?W?E) + ?SW where ?IA is the initial assessment failure rate (based on "RACRates" component failure rate models incorporated into PRISM) for the system based on its parts and the remaining factors address parts processes (?P), infant mortality (?IM), environment (?E), design processes (?D), reliability growth (?G), manufacturing processes (?M), system management processes (?S), induced processes (?I), no-defect processes (?N), and wear-out processes (?W). ?SW is the software failure rate. Quantitative values for the individual factors are determined through an extensive question and answer process intended to benchmark the extent that measures known to enhance reliability are used in design, manufacturing and management processes.
See Quanterion Solutions Inc. |
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| Procedural Event Analysis Tool (PEAT) | PEAT is a structured, cognitively based analytic tool designed to help airline safety officers investigate and analyse serious incidents involving flight-crew procedural deviations. The objective of PEAT is to help airlines develop effective remedial measures to prevent the occurrence of future similar errors.
The PEAT process relies on a non-punitive approach to identify key contributing factors to crew decisions. Using this process, the airline safety officer would be able to provide recommendations aimed at controlling the effect of contributing factors. PEAT includes database storage, analysis, and reporting capabilities.
See Boeing News. |
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| Procedure Analysis | Procedure Analysis is a step-by-step analysis of specific procedures to identify hazards or risks associated with procedures. The technique is universally appropriate. [Tarrents, 1980] |
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| Production System Hazard Analysis | Production System Hazard Analysis is used to identify hazards that may be introduced during the production phase of system development which could impair safety and to identify their means of control. The interface between the product and the production process is examined The technique is appropriate during development and production of complex systems and complex subsystems [Tarrents, 1980] |
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| Prototype Development | Prototype Development provides a Modeling/Simulation analysis the constructors early pre-production products so that the developer may inspect and test an early version. This technique is appropriate during the early phases of pre-production and test. |
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| Qualitative Assessment | A collective term for the various methods of assessing causes, severities, and likelihood of potential Failure Conditions. Typical types of analysis include Design Appraisal, Installation Appraisal, FMEA, FTA, DD, Reliability Block Diagrams, etc. |
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