In order to efficiently use available runway capacity while avoiding undue congestion within terminal airspace, systems of flow control and en route metering have been implemented. Recent work in automation has attempted to extend traffic flow planning to provide precise scheduling of traffic flow within the terminal area itself (from the metering fixes to the runways). The goal of this more detailed terminal scheduling is more efficient runway utilization. This article addresses an important practical question regarding the degree of precision required from the en route portion of such systems in order to allow the terminal scheduler to achieve its throughput benefits. The answer to this question determines the sophistication and rigidity required of en route automation and addresses the question of whether the success of new terminal automation is contingent upon improvements in en route metering. The method of analysis is mathematical modeling and fast-time computer simulation. A crucial parameter is controllability, which expresses the largest flight delay that the terminal scheduling can impose within the airspace available to it. The analysis reveals that achievable run-way utilization depends upon the type of metering employed, the available controllability within the terminal, and the extent to which controllers can be expected to intervene to handle transient peaks in arrival rates that cannot be handled by the automation. The major conclusion of the study is that in order to fully utilize a runway, the standard deviation of the errors in arrival time at the metering fixes should be kept to about half the terminal controllability. For the airports studied, there seems to be sufficient controllability available to allow a terminal scheduler to operate the runways at essentially full capacity when a metering system, even with modest delivery precision, is operating in the en route area.