How can open source Software and safety critical systems work together? DFS GmbH relies on Linux for its core air traffic control systems. We have succesfully managed to standardize a highly reliable, modular operating system and hardware platform at DFS. In a brief overview we explain the challenges, technical and non-technical ones, we have faced getting to the modular platforms. What approaches did we take and why? Which ones did work out in the long end? We will cover a broad range of aspects ranging from hardware life cycles, application lifecycles, regulations, deployment solutions, user acceptance, cost cutting and testing.