This article is the fourth in a series of papers that address the potential application of international generic functional-safety standard IEC 61508 to the transport sector, with a focus on the crucial requirements/specification phases of the system safety lifecycle in Part 1 of the Standard (IEC 61508-1). During the peer reviews of the three predecessor articles, questions were raised about the degree and extent to which some European Air Traffic Management and Rail safety-assessment standards and practices actually complied with the fundamental principles of IEC 61508-1; however, at the time, it had not been the intention of any of those three articles to address such questions, and it was left to readers to reflect on the matter. This article now returns to the subject of safety compliance, but in the context of Safety Assurance, and starts by developing a generic safety-assurance framework, based on classical systems-engineering practices and rigorous requirements-engineering principles, against which the IEC 61508-1 safety-assessment processes, and their equivalents in European Air Traffic Management and Rail safety standards, are judged in terms of their potential contribution to the safety case for typical safety-related transport applications.