Air traffic flow management (TFM) is a set of processes and procedures which seek to balance the demand for airspace resources with the capacity of these resources. Examples of resources are airports, sectors (airspace volumes managed by air traffic controllers), and fixes (imaginary points in space used for navigation). The Federal Aviation Administration (FAA) is continually looking for ways to provide new tools and techniques for TFM personnel. As the TFM function improves, flight efficiency improves, and the experience of the flying public is likewise improved. In this paper, we describe a simulation modeling exercise to assess the benefit, if any, of a proposed new feature of TFM called progressive planning (P2). P2 allows the flow manager to model the impact of multiple concurrent flow management actions. It is envisioned that the improved modeling leads to better decision-making, which leads to greater flight efficiency.