SAE ARP4754B / ED-79B - Guidelines for Development of Civil Aircraft and Systems 5.3.2: 5.3.2 Capturing safety requirements from the safety analyses

Safety requirements for each function, at aircraft, system, equipment or item level, usually comprise requirements for independence, numerical availability and integrity targets, criteria that no single failure is catastrophic, monitor performance, protective features, assurance levels, and limits on operation and maintenance; probabilistic requirements are usually handled by budgeting. They are established from the PASA and PSSA results, mostly by direct assignment from the failure categories, with relevant combinations chosen without examining every irrelevant one. Assumptions identified by the safety analysis (about what a system can do, about features of some other system, or about crew or maintenance procedures yet to be written) are managed to closure, at system level for capabilities within a system and at aircraft level otherwise, with the confirmation returned to the safety analysis that raised the assumption; managing them usually leads to requirements whose successful verification confirms the assumption.