Goal-based approach

Ultimately, success will be defined by a particular study s goals and thus vary from one study to another. Table 4-1 outlines two approaches for determining and measuring criteria of success adaptable to specific projects a goal-based approach proposed by Weinstein and Sandman (1993 also see Rohrmann 1992) and a process-based approach focusing more on whether... 

An effective goal-based approach to risk management requires the application of judgement made by competent personnel taking into consideration the available evidence. But wherever human judgement is called for it leaves us susceptible to outside influences. Bias, in the context of CRM, is the tendency of an individual to make decisions based on factors other than objective evidence. 

The failure target or goal-based approach (Kritzinger (2006), Chapter 6) found in standards such as FAR25.1309. 

One of the most important limitations of ISO 11064 was that the scope of the standard was inappropriate for lO. This supports the opinion of some of the interviewees who stated that the standard was out of date compared to current technology. This finding supports our proposal to shift to a more goal-based approach. 

Goal-based software safety cases have seen take up and interest shown from other sectors. In 1998 the UK CAA Safety Regulation Group drafted a goal based approach to the regulation of air traffic management systems and its proposals are contained in CAP 670 SWOl, Regulatory Objectives for Software Safety Assur-... 

Finally, the Ensurance strand corresponds to the activities of those personnel responsible for developing the software. We have deliberately avoided providing explicit guidance for ensurance activities, as this would not be in keeping with the goal-based approach of DS 00-56. In practice, the remit of these activities may overlap. For example, performing hazard analysis and deriving safely requirements will require interactions between activities in all three strands. 

Goal-based approach. This approach treats safety from basic principles. It manages safety by identifying failures, assessing their severity and allocating appropriate safety levels that need to be systematically accomplished (see Chapter 5). It is often used in completely new situations or modified existing situations. 

The goal-based approach to safety is applied as follows ... 

So, although the goal-based approach provides a designer with acceptable levels of safety which need to be accomplished in the design (as in Chapter 8), the user of the system will need to conduct further assessments (as in Chapter 9) to consider how the system is put into operational use and what risks said use will hold. 

The goal-based approach (commonly used in the aviation and nuclear industry for the certification of their products) emphasises the frequency of an undesired event (e.g. system failure). 

Once a hazard is identified, we need to decide on the severity of the hazard (if we are using the goal-based approach) or the severity of the potential accident (if we are using the risk-based approach). The severity is determined by considering the effect (or harm) of the potential outcome of the hazard within the context of the system state. For this explanation to make sense, a few clarifying explanations are needed ... 

For the goal-based approach, all deviations will require dispensation from the approval authority. 

There is no one correct way of conducting a safety assessment. It all depends on the system complexity and on the safety assessment approach utilised (see Chapter 2). That does not mean to say that the assessment has to be analysed from a single approach only for, more often than not, a combined approach is far more feasible to identify and analyse the range of possible hazards (see Chapter 6). The following section will broadly contrast/compare the maimer in which the goal-based approach (Chapter 5) and the risk-based approach (Chapter 4) are applied during a system safety assessment. 

Bear in mind that the goal-based safety criteria used to satisfy JAR25.1309 and JSP553 para 1.38 is not directly compatible with the risk-based approach required by the safety case. In this case, the former should rather be used to identify contributing factors within a sequence of events which may lead to an accident. The goal-based approach is thus a useful source of failure/event inputs, along with their probability of occurrence. 

Note that this is the goal-based approach as discussed in Chapter 5. 

Loss/malfunction of a missile approach warning system (MAWS) may not affect the airworthiness of the aircraft, and could be classified as a minor failure condition (using the goal-based approach) and may be probable in occurrence. However, in accordance with DEE STAN 00-56, this loss could cause loss of the platform as no warning would result in no evasive or protective action, and should thus be classified as a catastrophic failure condition, which should be extremely improbable in occurrence. 

In Chapter 1, we consider the legal issues associated with system safety. The purpose of this chapter is to reinforce the liabilities assumed in the generation of safety related documentation. In Chapter 2 we attempt to put the term safety into perspective, and the basic approaches used to achieve it. The next three chapters will then explore three of these approaches the use of Regulatory Standards is explored in Chapter 3 Chapter 4 considers the risk-based approach, which is widely adopted in the military industry as well as by Health Safety specialists Chapter 5 introduces the civil aeronautical approach to safety assessments, which (for the want of a better term) we shall call the goal-based approach (in contrast to the risk-based approach in Chapter 4) as it provides clear goals (i.e. failure probability targets) for system designers to achieve. 

The next two chapters consider the generic approach to two frequently asked for deliverables. Chapter 8 considers the system safety assessment (SS A), which is usually required for the certification of a new/modified system. In the civil arena, the SS A is often based on the goal-based approach. In contrast, the safety case in considered in Chapter 9. The safety case is the document that manages (via the risk-based approach) the major hazards that an operator/maintainer of a system/facility faces, as well as the means employed to control those hazards. 

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