This paper presents a metric for measuring inefficiencies in flight trajectories that can be managed through Air Traffic Control (ATC) actions. Development of the prototype metric builds on prior international research. This paper shows that a similar metric can be developed, calibrated, and used to assess the operational efficiency of flights in the National Airspace System. The trajectory inefficiency metric estimates, for a large set of flights, the impact of various maneuvers observed from 4D flight trajectories on the resulting flight fuel efficiency. Several designs for the metric are explored. One advantage of using trajectory inefficiency scores is the relative ease of computation without requiring significant data inputs, assumptions, and modeling capabilities. The trajectory inefficiency metric does not eliminate the need for high fidelity flight fuel burn models; however, its simple design allows it to be useful for a variety of analyses and performance assessments.