Many Air Navigation Service Providers (ANSPs) aim to report on the number of continuous descents conducted in their administered airspace. The method with which this reporting is undertaken varies between ANSPs, but often the metric includes measuring the distance flown at level altitude. While such a metric tests if a descent was continuous, it does not necessarily mean the descent was also efficient. In this paper a metric and deriving algorithm will be proposed that tests if a descent was a managed descent. The major difference between a managed descent and a continuous descent is that a managed descent is performed in a predictable manner to a pre-determined plan by the aircraft's Flight Management System (FMS). A managed descent is in general continuous, but not necessarily vice versa. Often, whenever it is referred to continuous descent, it is the predictability of an automation managed descent that the airspace operator ultimately wants to achieve, and what an ANSP should facilitate. Derivation of the proposed metric algorithm and its application is demonstrated based on flight data from Australia and the United States. While the first basic implementation of the metric has yet a number of limitations, its application identified differences between the efficiency of descent trajectories where the conventional metric, in terms of detecting level segments, did not. In addition, application on US flight data demonstrated how the metric can assist in analysing the performance of ground-based trajectory prediction tools.