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 An Introduction to Tools and Techniques Minimize

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.

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 Tools and Techniques Minimize
 NameSorted By Name In Ascending OrderDescription
Modified Pilot Subjective Evaluation (MPSE)Human Factors evaluative tool
Features custom modifications of the PSE which permit it to be adapted as necessary to meet the specific requirements of a certification while retaining the proven elements of the PSE.
Monte-Carlo Analysis (as used by FAA for Fuel Tank Safety Assessments)Analytical method to determine flammability exposure time of a fuel tank. The percentage fleet flammability exposure result can be used to determine if the fuel tanks exist in a flammable state for a long period of time, thereby requiring more rigorous analysis in the SSA.

Spreadsheet that simulates uncertain parameters by randomly selecting values from distribution tables. The calculation is performed repetitively and averaged to approximate real conditions.

See also Mathworld Monte Carlo page.
NASA-Task Load IndexHuman Factors evaluative tool
Network Logic AnalysisA method to examine a system in terms of mathematical representation in order to gain insight into a system that might not ordinarily be achieved.

The technique is universally appropriate to complex systems. [Tarrents, 1980]
NPRD-95The Nonelectronic Parts Reliability Data (NPRD-95) databook is a widely used data book published by the Reliability Analysis Center that provides a compendium of historical field failure rate data on a wide array of mechanical assemblies.

The document provides detailed failure rate data on over 25,000 parts for numerous part categories grouped by environment and quality level. Because the data does not include time-to-failure, the document is forced to report average failure rates to account for both defects and wearout. Cumulatively, the database represents approximately 2.5 trillion part hours and 387,000 failures accumulated from the early 1970's through 1994. The environments addressed include the same ones covered by MIL-HDBK-217; however, data is often very limited for some environments and specific part types. For these cases, it then becomes necessary to use the "rolled up" estimates provided, which make use of all data available for a broader class of parts and environments. Although the data book approach is generally thought to be less desirable, it remains an economical means of estimating "ballpark" reliability for mechanical components.

See Quanterion Solutions Inc..
NSWC-94/L07Handbook of Reliability Prediction Procedures for Mechanical Equipment developed by the Naval Surface Warfare Center - Carderock Division This handbook presents a unique approach for prediction of mechanical component reliability by presenting failure rate models for fundamental classes of mechanical components

Examples of the specific mechanical devices addressed by the document include belts, springs, bearings, seals, brakes, slider-crank mechanisms, and clutches. Failure rate models include factors that are known to impact the reliability of the components.

For example, the most common failure modes for springs are fracture due to fatigue and excessive load stress relaxation. The reliability of a spring will therefore depend on the material, design characteristics and the operating environment. NSWC-94/L07 models attempt to predict spring reliability based on these input characteristics.
Occupational Health Hazard Analysis (OHHA)Identifies health hazards and recommends provisions such as ventilation, barriers, protective clothing, etc
Operability AnalysisThe aim of carrying out Operability Analysis is to highlight any issues that have a bearing on the operability of a system/equipment. An Operability Analysis should act designed for operation in the simplest and easiest way possible.
Carrying out an Operability Analysis involves the following:
  • Task Analysis
  • Workload analysis
  • Human reliability analysis
  • Taking due account of the prevailing environmental conditions
Effort invested in the Operability Analyses will vary with the criticality of the equipment, its interfaces and interactions with other equipment. Therefore the scope of operability assessments can be restricted to a single task or cover a range of tasks.

Methods include:
  • Anthopemetrical Studies can be used to provide known physical data on the population to assess workplace layout and architecture.
  • Rapid prototype modelling permits varied configurations to be tested over comparatively short timescales. This technique permits feedback from subject matter expert to be incorporated into the model, and assessed promptly, before possible inclusion into the design.
  • Task analysis involves a study of the workforce (operators) to ascertain what is required to achieve the system goals. This allows comparison between the task demands and the operator's capabilities.
  • Workload analysis is an analysis of the demand placed on the operator by the task requirements.
  • Human reliability analysis recognises the critical area where human error may affect performance.
  • Operational scenario analysis is an analysis that the activities required to be undertaken, can be successfully completed using the manpower and facilities provided for the purpose.
See Technical & Information Productions.
Operating & Support Hazard Analysis (OSHA)The analysis is performed to identify and evaluate hazards/risks associated with the environment, personnel, procedures, and equipment involved throughout the operation of a system [Tarrents, 1980]

Evaluates hazardous operating, maintenance and support tasks by systematically evaluating each phase of operation and support. Can be divided into 2 separate analyses:
  • The Operating Hazard Analysis
  • Support Hazard Analysis
Pareto AnalysisA ranking technique based only on past data that identifies the most important items among many. Uses the 80-20 rule, which states that about 80% of the problems are caused by about 20% of the causes.
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