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The Initial Investment Decision (IID) is the point at which the Joint Resources Council (JRC) approves or selects the best alternative that both meets the required performance and offers the greatest value to the FAA and its stakeholders. To support the IID, the PO must complete a CSA and, through Safety and Technical Training, 3  inform the JRC of the safety risk acceptability of each alternative. 

A CSA is related to but different from an OSA. Where an OSA defines the target level of safety irrespective of the solution, a CSA provides an estimation of the potential safety risk associated with each proposed solution alternative. 

## 3.2 Overview 

The CSA is a risk assessment that defines severity and likelihood of the initial and predicted residual risk of each proposed alternative. The CSA builds upon an OSA (if one was previously conducted) by using the top-level Functional Analysis (FA) that was developed before the OSA. The FA is decomposed at least one more level in order to further expand the Preliminary Hazard List (PHL) 4  produced in the OSA. If an FA has not been previously developed, the PO must develop one as input to the CSA. If an OSA has not been previously conducted, then the PO must develop a PHL in the CSA. Figure D.1 provides an overview of the CSA development process. 

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## 3.3 Use of Results 

The results of the CSA are used as inputs to the items described below. 

## 3.3.1 Preparing/Revising the Program Requirements Document 

Controls from the reference case and generic safety requirements that are identified through the CSA process for each selected alternative (as yet solution agnostic) must be included in the Program Requirements Document. Related changes by alternative analyses must be 

