PACTS-21 is a collaborative research programme co-funded by the DTI and a number of aerospace companies. One of its aims is to develop the technologies, infra-structure and standards that will be needed to develop the civil aircraft of the future, viz. those entering service in the 21st century. The next generation of systems may include highly integrated digital avionics under software control, a concept known as integrated modular avionics (IMA). To date the activities of the PACTS systems engineering (SE) working group have included a top level review of existing system engineering processes, tools and metrics to determine their relevance to the aerospace industry, and the provisional definition of an SE process model that better reflects the specific requirements of IMA systems development. This paper reports the work undertaken by the group, outlines the process model, and summarises the group's findings and conclusions. (7 pages)