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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
What if AnalysisWhat-If Analysis methodology identifies hazards, hazardous situations, or specific accident events that could produce an undesirable consequence. [Tarrents, 1980]

A problem solving approach that uses loosely structured questioning to (1) suggest upsets that may result in accidents or system performance problems and (2) make sure the proper safeguards against those problems are in place

Typical qualitative probability terms are:
  1. Probable Failure Conditions are those anticipated to occur one or more times during the entire operational life of each aeroplane.
  2. Improbable Failure Conditions are divided into two categories as follows:
    1. Remote. Unlikely to occur to each aeroplane during its total life but which may occur several times when considering the total operational life of a number of aeroplanes of the type.
    2. Extremely Remote. Unlikely to occur when considering the total operational life of all aeroplanes of the type, but nevertheless has to be considered as being possible.
  3. Extremely Improbable Failure Conditions are those so unlikely that they are not anticipated to occur during the entire operational life of all aeroplanes of one type
What-If/Checklist AnalysisWhat-If or Checklist Analysis is a simple method of applying logic in a deterministic manner. [Tarrents, 1980]
Why Because AnalysisWhy-Because Analysis (WBA) is a rigorous technique for causally analysing the behaviour of complex technical and socio-technical systems. Its primary application is in the analysis of accidents, mainly to transportation systems (air, rail and sea). It is also used in the Ontological Analysis method for safety requirements analysis during system development.
WBA is based on a rigorous notion of causal factor. Whether one event or state is a causal factor in the occurrence of another is determined by applying the Counterfactual Test. During analysis, a Why-Because Graph (WB-Graph or WBG) is built showing the causal connections between all events and states of the behaviour being analysed. The completed WB-Graph is the main output of WBA.
Zonal Safety Analysis (ZSA)/Zonal Hazard Analysis (ZHA)CCA technique which specifically considers physical proximity of different technologies. Theoretical and visual examination of each physical zone to ensure that interference and interactions with adjacent systems do not violate the independence requirements.

Used to:
  • determine compliance with the installation rules,
  • identify any potential cascade failures due to system interaction,
  • identify any potential areas for maintenance errors,
  • identify potential areas for system malfunction due to environmental factors.
This technique is used to look at the complex interactions that can occur between high-energy systems and is specifically concerned with their physical position in relation to each other.
The Zonal Hazard Analysis techniques are also used to assess the effects of the proliferation of hazards into adjacent physical areas or compartments. They can be used to identify the routes by which the hazards may spread and in so doing, solutions can be developed to control and mitigate the effects of the hazard.

See SAE ARP5754 p38.
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