alternatives are eliminated as discriminators, leaving those that differ to be of prime importance to the CSA. 

## 4.1.3 FA 

An FA, as described in the FAA SEM, is used to examine the functions and sub-functions of a system solution that may accomplish the system’s operation or mission. An FA describes what the system does (not how it does it) and is conducted at a level needed to support later synthesis efforts. Products from the FA, such as the Functional Flow Block Diagram and N 2  diagram (although other techniques may be used to diagram system functions), are further matured as the system’s lifecycle progresses and may be used when developing the CSA. If the alternative solutions are sufficiently diverse, then the functional architectures (as yet solution agnostic) begin to exhibit significant differences that affect safety risk, making the CSA valuable. Should no difference in safety risk be determined, the CSA no longer helps to distinguish a preferred alternative, which leaves outside Business Case factors as sole determinants. 

Note : The FA involves an iterative process that results in an increasingly refined functional architecture. The functional architecture cannot be finalized until the system’s final requirements are completely defined. This most likely is after the CSA is performed. 

## 4.1.4 Functional Hazard Assessment 

A Functional Hazard Assessment (FHA) is a methodical approach to identifying credible operational safety effects through the assessment of system or sub-system functions and failure conditions. The FHA identifies and classifies the system functions and safety hazards associated with functional failure or malfunctions. It identifies the relationships between functions and hazards, thereby identifying the safety-significant functions of the system as well as the hazards associated with that functionality. This identification provides a foundation for the safety program to scope additional safety analyses. 

## 4.2 CSA Development Process 

## 4.2.1 Describe the Solutions/Alternatives 

Describe the solutions under study in terms of the 5M Model, per the SMS Manual. At this point, a number of different architectures and alternatives have been identified to meet the operational requirement. Describe each alternative in sufficient detail to ensure the audience can understand the proposed solution. 

## 4.2.2 Make Assumptions Only If Specific Information Is Not Available 

As necessary, make assumptions that are conservative in nature and clearly identified. Make them in such a manner that they fairly distinguish among the alternatives which aspects do or do not adversely affect the safety of the solution. 

## 4.2.3 Perform/Expand the FA/FHA 

Perform an FA/FHA (or expand the one previously developed) in accordance with the FAA SEM and Safety Risk Management Guidance for System Acquisitions Appendix C. Attempt to match similar and unique causes associated with each hazard into a firm list of unique events that may be adequately addressed by existing functions or by postulating new low-level system functions. This analysis results in complete sets of hierarchical functions that alternative system solutions must perform. 

Look for matches between system function and mitigation of all causes (within system bounds). Organize causes that fall beyond system bounds into assumptions and constraints for 

