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coordination with external NAS entities. Though all such external dependencies may be noted, it may not be possible to address them within the bounds of this system. 

Analyze all external causes that cannot be mitigated within system bounds for faulty assumptions that may invalidate the efficacy of the best solution that could be engineered. Adjust concepts as needed until a good fit is obtained between hazard causes that can be mitigated within this system boundary and operational plans for reaching adequacy of every listed (known) external constraint. 

Decide which alternative solutions remain viable after a cursory look at safety. Discard any potential solution “fragments” 7  that inadequately address safety concerns. 

## 4.2.4 Develop a Hazards List 

From the FA and solution description, refine and expand (as necessary) the partial PHL developed in the OSA (assuming an OSA was conducted). If a partial PHL was not previously compiled, then develop one as described in the SMS Manual. Carry over any valid OSA-identified hazards / causes / solution states / severity ratings to the CSA. If any OSA hazards need to be deleted or modified in the CSA, provide a supporting rationale as to why this must be done. Table D.1 presents a sample hazard list that has been expanded/modified from an OSA. 

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## 4.2.5 Assess Risk in the Context of Each Alternative 

Evaluate each hazard-alternative combination (including the reference case) for risk differences using the definitions and principles contained in the SMS Manual. Evaluate the hazard severity in the context of the worst credible conditions. Remember, severity can and should be defined independently of the likelihood of occurrence. Evaluate the likelihood of the hazard conditions resulting in an event at the highest level of severity and not simply the probability of any hazard occurring. 

## 4.2.6 Document the Assumptions and Justifications 

Clearly define which adverse events are to be tracked as the best indicators of safety. Identify how to measure adverse events and provide any baseline measures prior to the proposed 

