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Figure 3.4 depicts the potential scope and level of Safety Risk Management (SRM) required based on the potential impact and scope of the NAS change. The lowest-tiered safety assessments focus on identifying hazards associated with individual projects/programs and analyzing individual changes to the NAS that are often associated with new system acquisitions. The middle tier is the capability level. Examples of capabilities include Performance Based Navigation, Surface Operations, or Data Communications. Here, system safety risk assessments become more complex, considering multiple combinations of dependent functions. The top tier represents high-level SRM activities associated with service levels and/or domains to reflect a strategic view of safety across the NAS. Safety management at this level is more static in nature (i.e., essentially non-recurring system safety engineering). It employs high-level functional hazard analyses to identify NAS-level hazards and safety requirements that flow down vertically to the other-tiered levels. 

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