Descent and Terminal Area

Continuous Descent Arrivals

The development of Continuous Descent Arrivals (CDAs) was one of the first main projects of the Air Transportation Laboratory. With increasing fuel prices and a heightened awareness for environmental and noise concerns, airlines and air traffic control are looking at various methods to improve an aircraft’s performance during flight. One such opportunity presented itself during the descent phase of a flight. Currently, aircraft perform what may be termed a ‘step descent’ to the runway. That is, aircraft do not descend constantly during the approach to the runway; instead, they descend from one altitude to another, continue in level flight until a certain point, and then resume their descent to the runway or another altitude. This method is not fuel-efficient since an increase in thrust may be needed to maintain altitude during a level flight segment and by increasing thrust, more noise and pollutants are produced. Such a procedure is in place for many reasons, including airspace restrictions and traffic volume.

CDAs were developed with the goal of minimizing these level segments and allowing aircraft to descend ‘continuously’ to the runway, without having to level out at a certain altitude. An analogy to such a procedure is driving down a hill in a car, with the foot off the accelerator and letting the car coast down the hill without driving over any flat regions of road. To design a CDA, a fast-time simulator has been created in Matlab and is used to simulate the trajectories that aircraft would take if they flew such a procedure. These trajectories are then provided to air traffic control, who then informs the ATL as to whether the designed procedure fits into current airspace restrictions. If so, the procedure is then flight tested in aircraft simulators, followed by a live demonstration before publication. If not, a redesign is conducted to ensure compliance with airspace restrictions.

Currently, CDAs designed by the Air Transportation Lab are in use at two airports in the US: Louisville International Airport and Los Angeles International Airport. Results from Louisville have shown that up to 1000 lbs of fuel can be saved per flight along with a substantial decrease in noise over a flight path flown by a B767-300. At Los Angeles International Airport, most flights flying in from the East Coast of the US utilize the designed procedure and along with air traffic control, are very happy with the arrival. Airports currently involved in CDA development include Atlanta’s Hartsfield-Jackson International Airport and San Diego International Airport, with a CDA flight test conducted in Atlanta during spring of 2007 and upcoming tests beginning in August 2008. Delta Air Lines has been a key partner in the development of these procedures, participating in both the flight test portion, and allowing the ATL to use its flight simulators. The fuel saving potential at Hartsfield-Jackson International Airport is enormous due to the number of flights flown by the dominant carrier, Delta Air Lines.

CDAs are an important part of the Next Generation Air Transportation System (NGATS) of air traffic control. The goal by 2020 is to implement as many CDAs as possible at airports around the US, possibly providing a substantial fuel savings to airlines, as well as alleviating environmental and noise concerns for communities around airports.

Treating Clusters of Nearby Airports as a Single Entity (Metroplex) to Alleviate Congestion

In an ideal situation, air traffic flows to and from a given airport would be independent of the traffic flows to and from other airports in close proximity, and the flight trajectories of aircraft would be optimized for economic and environmental efficiency based on factors such as aircraft performance, winds, direction the aircraft is arriving from or departing to, and distance to/from the airport runways. However, in the National Airspace Systems (NAS) of today, where significant airspace is required for a single aircraft path, the traffic flows to and from multiple airports in close proximity can and do interact. This interdependency of air traffic flows of closely-spaced airports defines what the Joint Planning and Development Office (JPDO) terms a metroplex. This research endeavors to agree upon the measurements and conditions that define a metroplex, and a possible example of such an area is the heavily trafficked Northeast Corridor with Newark, LaGuardia, and JFK airports all within close proximity. Once the definition of a metroplex area has been decided, this project will examine the factors that have the greatest impact on on-time performance and find ways to address these factors in the Next Generation Air Transportation System (NGATS), the overhaul of the current air traffic management system. In addition, specific NGATS concepts are being examined in the context of metroplexes, including 4-D trajectory-based operations, performance-based services, and increased environmental awareness using the advanced airport and terminal airspace demand projection, modeling, and simulation capabilities of the team. The results of these studies will be evaluated in terms of the classification scheme described in the previous objective so as to simplify the comparison of various possible NGATS scenarios.

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