Flight deck descent procedures were developed for a field evaluation of the CTAS Descent Advisor conducted in the fall of 1995. During this study, CTAS descent clearances were issued to 185 commercial flights at Denver International Airport. Data collection included questionnaire responses obtained from participating pilots and observations recorded in the cockpit during CTAS descents. Results indicate pilots' general acceptance of the procedure. Several problems were uncovered regarding

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... ce understanding, readbacks, and the acceptability of top of descent point and descent speed clearances in a few situations. This paper describes the descent procedures and phraseology developed to support the field test and presents the nature of the problems encountered. BACKGROUND The CTAS Descent Advisor The Center-TRACON Automation System (CTAS) is a suite of decision support tools under development by NASA and the FAA to improve the efficiency of descents, aid in aircraft sequencing, and increase the rate at which aircraft can land at an airport (Erzberger, 1994) . One component of CTAS, the Descent Advisor (DA), uses aircraft performance models, atmospheric forecasts, current air traffic conditions, and individual airline preferences to predict aircraft trajectories to the metering fix at the TRACON boundary (Williams & Green, 1991) , (Green & Vivona, 1996) . The Descent Advisor computes an arrival time at the metering fix for each aircraft that will result in aircraft arriving at the metering fix efficiently sequenced and spaced. The DA then calculates a descent trajectory and descent speed each aircraft should fly in order to meet its scheduled arrival time. The DA provides the controller with three parameters that define these trajectories: an Assigned Descent Point, an Assigned Descent Speed and a speed and altitude crossing restriction at a metering fix. The achieved arrival time accuracies depend on how well each aircraft's actual descent path and speed match the specified trajectory.