This paper assesses the impact of a major expansion in airfield capacity at DallasFort Worth (DFW) airport. In October 1996, a new runway was commissioned, and the airspace was entirely reconfigured. Our study of the benefits of the expansion is retrospective and based on empirical data and hence provides a useful check on predictive and model-based studies. Also, it pays considerable attention to adaptations made by airlines. Central questions in our research are whether operational impacts and airline adaptations can be observed in the DFW case, and how to define metrics that may capture them. We developed several new metrics and used them, in conjunction with existing metrics, to measure the impacts and adaptations. We found that average effective travel time from the scheduled departure time to the actual arrival at DFW and hence the average delay did decrease after the capacity expansion, but only under inclement weather conditions. However, no significant reductions in delay against schedule were observed. The daily maximum rate of operations of American Airlines, the dominant carrier at DFW, increased. Also, major airlines operating at DFW collectively scheduled their daily operations with a higher concentration (across the whole day) than the earlier levels in 1996. Average passenger transfer time of American s flights at DFW improved but the improvement did not last long. Overall, it appears that the impacts and adaptations were more modest than expected, perhaps as a result of confounding events. The metrics and methodology are applicable to any such study about any other airport.