Airport strategic planning is currently a rather cumbersome process, due to the complexity of the airport system and the wide variety of stakeholders involved. These stakeholders include airport authorities, air traffic service providers, airlines, regulatory agencies, and the general public. Historically, the airport planning process has usually been conducted with only a single objective in mind – that capacity should match revealed demand. Nowadays, the planning process is driven by many more objectives, such as safety, affordability, financial and economic benefits, and environmental impact, which have to be balanced. Currently, no integrated software tools, let alone decision support systems, are available that can be used to develop strategic plans for airport development. The HARMOS DSS has been developed to fill this gap. This paper demonstrates how the architecture of the HARMOS DSS supports an airport operator and its stakeholders to think and work together on airport strategic planning problems. We'll show how the design of the architecture involves stakeholders in the planning process, supports dealing with the uncertain future, and improves the efficiency of problem solving.