Avionics systems are currently undergoing a transition from single core processor architectures to multi-core processors. This transition enables a reduction in size, weight and power (SWaP) and the use of common processing platforms, providing multiple potential benefits for programs in terms of reduced costs, spares management and obsolescence. However, avionics hardware and software certification policies and guidance are evolving as research and experience is gained with multi-core processor architectures. In this paper, we discuss what is unique about multi-core processors and define the requirements for a commercial real-time operating system (RTOS) for multi-core certification. We present a collaborative approach undertaken by a leading avionics system supplier and a leading safety-critical RTOS supplier in the development of a realtime multi-core avionics system. We discuss the approach taken in order to achieve DO-178C DAL A safety certification on an FAA Programme of Record. We also present the approach taken to comply with FAA CAST-32A objectives, including investigation of multi-core interference channels, documentation and analysis of results, as well as methods to support independent third-party certification.