The Federal Aviation Administration uses two manual systems to meansure air traffic control system performance and is now in the process of developing a third, which uses its recently intalled computer equipment to collect performance data. Our objective is to obtain insight and understanding about the utilization of capacity, the causes of air traffic delays, the magnitude of delays, and the locations at which they occur so that air traffic control can be performed more efficiently. The first system, started in 1968, identifies aircraft delays of 30 min and where, when, and why they occur. The second system, implemented in late 1975 at major airports where delays occur, utilizes hourly airport runway capacity standards to asess performance when demand reaches or exceeds capacity. Performance is indicated by an index comparing actual aircraft services to a standard. The system also provides data on delays of 15 min or more, causes for delays, and substandard performance as measured by the performance index, runway utilization, and weather data. The third system, now in early stages of development and testing, will collect accurate delay data on aircraft flying into major airports. This delay data base will be the most comprehensive and accurate of the three systems and will provide total information on aircraft delay. Coupled with the data provided by the second system, it will give a sophisticated and accurate performance data base that will indicate system performance and areas for improving the air traffic control system.