# Analytical Model for Enhancing the Adoptability of Continuous Descent Approach at Airports
## 1 Introduction
FedEx, another express transport and delivery company with one of the largest civil aircraft fleets in the world, has been using CDA at their World Hub, Memphis International Airport. Their use of CDA at Memphis reduced flight time by 2.5 min for each flight, and this translated into cost savings of $105 million based on their field study from 2006 to 2009 [10]. These operational, economical, and environmental benefits from CDA procedures have made it a cornerstone in some aviation modernization programs at the national (e.g., FAA's Next Generation Air Transportation System, \"NextGen\"), continental (e.g., EU's Single European Sky Air Traffic Management Research, \"SESAR\"), and international (e.g., United Nations' International Civil Aviation Organization, \"ICAO\", Continuous Descent Operations, \"CDO\", initiative) levels. Although considered as an effective Noise Abatement Procedure, CDA is not widely implemented, especially during high density operations [11; 12]. Due to safety considerations [13; 14; 15], CDA procedures may require more separation between aircraft arrivals, which may affect the airport arrival rate and runway throughput [16; 17]. The larger separation spacing for a CDA aircraft is mainly due to two reasons: the difficulty for air traffic controllers to predict the future position of an aircraft with significantly variable speed [6] and the inability of the pilot to quickly decelerate during descent [18]. Although CDA has been proven to be feasible and without increasing the required spacing between aircraft under light traffic conditions, such as night-time operations [6], aircrafts flying CDA are most likely to be spaced further apart under heavy traffic conditions. Thus, CDA implementation has been limited to low to moderate traffic levels. During these low traffic conditions, CDA has been used at more airports. To increase the use of CDA, several studies in the literature have used various approaches, such as simulation [19], mathematical modeling [15; 20], and flight trials [6; 14], to quantify CDA's benefits and/or suggest solutions to the problem of increasing CDA's usage at airports through the analysis of sequencing and merging [21], merging and spacing [18], scheduling and conflict detection and resolution [16], time and aircraft energy management during descent [22], fuel and flight-path management [23; 24], and ground-to-air air traffic network vulnerability [25]. Other literature has applied quantitative methods to improve aircraft operation [26; 27]. However, insufficient attention has been given to developing a quantitative measure to enable air traffic controllers to make informed decisions on safely accepting more CDA operations. The contribution of this work is the development of a model that addresses this gap in CDA research and that helps air traffic controllers determine brief periods of time (e.g., 15-min periods) in which the vast majority of arriving flights may land using CDA. These time periods are based on time of aircraft arrival into the TMA. An aircraft entering the TMA during one of those time periods may begin its continuous descent upon entering the TMA while completing its continuous descent during a later time period, in which then-arriving aircrafts are no longer using CDA. In fact, although the time to descend using CDA depends on several factors (e.g., aircraft weight), it may be longer than 15 min. Data from previous authors [28; 29] implies the time to descend using CDA may be 20-30 min. Special attention is dedicated to factors that have a significant impact on CDA implementation, such as airspace structure around airports, airport arrival rate, and distance requirements for longitudinal separation between approaching aircrafts. Analyzing airspace structure around an airport offers a systematic way of developing an analytical model that adequately captures the elements associated with descent and approach procedures.