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.  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.  The results of the CSA are used as inputs to the items described below.  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  3. The ATO Chief Safety Engineer is responsible for this. 4. The concept of the PHL is explained in the SMS Manual. D_SRMGSA_202003 Originally published March 2020  Uncontrolled copy when downloaded  D-2 3.3  Use of Results 3.3.1  Preparing/Revising the Program Requirements Document  3.2  Overview Identified  alternatives OSAs FA FHA 4.2.1 Describe the  solutions/ alternatives 4.2.2 Make  assumptions 4.2.3 Perform/ expand the FA/FHA 4.2.4 Develop a  hazards list 4.2.5 Assess risk in  the context of each  alternative 4.2.6 Document the  assumptions/ justification for  severity/likelihood 4.2.7 Assess the  alternatives  4.2.8 Make  recommendations  4.2.9 Document the  CSA Figure D.1: The CSA Development Process 