A key challenge in increasing the autonomy of unmanned aircraft systems (UAS) lies in developing robust onboard decision-making capabilities within mission and contingency management (MCM) systems. Mission management enables the successful execution of operational goals while considering performance, safety, and regulatory constraints, whereas contingency management allows the UAS to handle plan failures, performance degradation, and system faults autonomously. Enhancing these capabilities can reduce reliance on human intervention and enable safe, scalable UAS operations. This paper systematically derives the key requirements for a highly autonomous MCM system. First, three distinct use cases – offshore wind farm delivery, regional cargo transport between fixed airports, and humanitarian aid distribution – are introduced that highlight the need for autonomous mission and contingency management in UAS. Second, requirements for a MCM system fulfilling these use cases are derived. A functional decomposition of MCM systems is performed, and state-of-the-art capabilities for each function are reviewed. Finally, gaps are identified to highlight opportunities for new MCM capabilities to advance the level of autonomy in UAS.