Orbital Critical Systems is a main contributor to the A400M mission computer, the main component of the Mission Management System (M-MMS). This complex airborne avionics system features an innovative IMA partitioning scheme based on ARINC-653. Our company was responsible for the development of several software partitions as required by a high-level specification baseline, providing all necessary evidences and artefacts for DO-178B airworthiness certification including low-level requirements, source code, test specification, validation campaign procedures and reports. The implemented functionality in the M-MMS includes communication equipment management and control (VUHF and HF radios), SATCOM datalink control and MIDS military datalink management. Another key achievement was the implementation of the Cargo & Aerial Delivery management system and ARINC-429 interface control partition.