The Safety Analysis and Risk Mitigation Process  Section 3  28 3.3_SMSM_201509 Originally published September 2015 Uncontrolled copy when downloaded 3.3.3  Defining the System / NAS Change  3.3.3.1  Describe the System and the NAS Change  3.3.3.1.1 Overview  3.3.3.1.2 Considerations when Defining the System The following are examples of information to consider when describing the system:  Complex NAS changes may require a detailed system description that includes numerous  charts, drawings, design descriptions, and/or narratives. Simple NAS changes may only require  one or two paragraphs describing the system and NAS change. The description must be clear  and complete before continuing the safety analysis. Questions to consider include:  As discussed, the system is always a component of some larger system. For example, even if  the analysis encompasses all services provided within an entire Air Route Traffic Control  Center, that Center can be considered a subset of a larger body of airspace, which in turn is a  subset of the NAS.  The system description provides information that serves as the basis for identifying all hazards  and associated safety risks. The system/operation must be described and modeled in sufficient  detail to allow the safety analysis to proceed to the hazard identification stage. For example,  modeling might entail creating a functional flow diagram to help depict the system and its  interface with the users, other systems, or sub-systems. System descriptions need to exhibit two essential characteristics: correctness and  completeness. Correctness means that the description accurately reflects the system without  ambiguity or error. Completeness means that nothing has been omitted and that everything  stated is essential and appropriate to the level of detail. • What is the purpose of the NAS change? • What issue is necessitating the NAS change? • How will the change be used/function in the NAS? • What are the boundaries and external interfaces of the NAS change or system? • In what environment will the system or NAS change operate? • How is the system or NAS change interconnected/interdependent with other systems? • How will the NAS change affect system users/maintainers? • If the NAS change is a waiver/renewal, how could other waivers in effect interact with it? • Average annual approaches to each runway • Fleet mix • Number and type of airport operations • Number of aircraft controlled (ground, pattern, and transitions) • Number of hours the airport operates and number of aircraft controlled under Visual Flight Rules versus Instrument Flight Rules • Availability and reliability of both hardware and software