Terrain following/terrain avoidance/threat avoidance/obstacle avoidance [TF/(TA)2/OA] is an inescapable penetration technology for future aircraft. Properly implemented low altitude tactics will increase survivability given the current dense and mobile threat environment. Numerous functional elements, computationally intense algorithms, flight safety considerations, and pilot acceptance characterize this system. These system integration issues demand that a real-time engineering simulation be exercised before aircraft implementation. This paper describes an initial terrain following/terrain avoidance (TF/TA) simulation which blends aggressive trajectory generation, control coupling for trajectory tracking, map navigation, and aircraft and flight control system dynamic elements. Functional partitioning between simulation computers, timing requirements, information flow and requirements for intercomputer communication, interface software and data transfer requirements are also described.