This paper describes how the air traffic management (ATM) problem is primarily temporal, sequencing arrivals at intervals such that the acceptance rate of a given runway is not exceeded. The current air traffic control automation efforts are based on time-based metering of arrivals to major airports in the National Airspace System (NAS). Such metering systems assist controllers and air traffic managers by extending the prediction and projection horizons beyond to what is within the capabilities of unaided human cognition and provide through a number of different interfaces early warnings of excessive demand and feedback on the effect of various responses. However, the procedures to manage excessive demand are difficult to administer and result in compounding delays and wasted resources. This paper describes an algorithm that computes customized transition trajectories for aircraft approaching a designated runway in a manner that ensures minimum regulatory separation between successive aircraft. Putative benefits of the algorithm include maximal use of available resources, dynamic transitions between free and controlled flight, and reallocation of functions between human controllers and automated systems.