The Advanced Trajectory Modeling project is studying how new data exchange capabilities can improve the trajectory models used by ground and aircraft automation systems. More accurate models support both Performance Based Navigation (PBN) and Trajectory Based Operations (TBO) concepts. The project has identified various aircraft intent and state data elements available from aircraft and Flight Management Systems (FMS) that could be downlinked to ground automation systems. These data are extracted from onboard avionics systems, and downlinked to ground automation systems, using technologies that are rapidly being adopted. Once downloaded, the data are used in advanced trajectory models to support Trajectory Based Operations (TBO). We are implementing these aircraft-derived data elements and trajectory model improvements in an exploratory simulation study to assess the capability for different aircraft types with different equipment capabilities to provide the data, and for ground automation systems to make use of the data to improve trajectory model accuracy. Our approach, using actual systems, provides both an initial assessment of feasibility and anticipated performance benefits. This paper provides background on the project and describes project progress to date.