Characterization of and Concepts for Metroplex Project

Metroplex project with NASA to help quantify issues and identify solutions

ATAC’s solution to understanding and evaluating metroplex operations

Metropolitan areas in the U.S. with high demand are often served by a system of two or more airports whose arrival and departure operations are highly interdependent. Such an airport system is referred to as a metroplex. The projected traffic growth in the coming years will increase the coupling of operations in the metroplexes that already exist, and will potentially create new metroplexes. The coupling of operations requires that the solution for the airspace structure surrounding, and the traffic flows to and from airports within, a metroplex must be solved cooperatively as a system.

ATAC was part of a larger NASA project to develop a deeper understanding of the constraints on metroplex operations that reduce capacity and to use this understanding to develop and evaluate new metroplex design and operational techniques to increase capacity in high-demand metropolitan areas. This increase in capacity is essential to enable the National Airspace System (NAS) to accommodate the air traffic demand projected in the Next-Generation Air Transportation System (NextGen) time frame. This accommodation will require research in not only airport operations and procedures but also high-density terminal airspace operations and procedures. The specific task objectives were as follows: 

  • Identify the dependencies and interactions among metroplex airports that affect metroplex operations.
  • Develop a classification scheme for metroplex dependencies.
  • Determine the impact that the introduction of NextGen concepts and capabilities will have on metroplex operations. 
  • Investigate new and innovative methods for significantly increasing the capacity of metropolitan airspace and airports.

Qualitative analyses and internal subject domain expert evaluations were employed to develop classifications of metroplex issues and airspace interdependencies. Quantitative metrics were developed to measure the intensity and types of interactions between metroplex airports and specific traffic flows.  Four metroplex sites surveyed:

  • Atlanta Large TRACON (A80)
  • Miami Tower/TRACON (MIA)
  • Southern California TRACON (SCT)
  • New York TRACON (N90)

With the identified candidate sites, a series of comprehensive metroplex site surveys were conducted. The goals of the site surveys were:

  • To develop a thorough understanding of the metroplex issues and constraints by studying real-world examples 
  • To catalog the traffic-flow dependencies and interactions at each site 
  • To document the best practices at each facility to handle metroplex issues, constraints, and dependencies

To collect information and model planned future developments relevant to the metroplex problem at each site, the Performance Data Analysis and Reporting System (PDARS) was used to analyze current traffic flows at each site. Selected concepts were modeled and tested using an Airport and Airspace Delay Simulation Model (SIMMOD). These tasks supported the following objectives:

  • Identify dependencies and interactions. 
  • Develop a classification scheme for metroplex operations.

Traffic-flow analysis was performed utilizing PDARS, which processes both en-route and terminal flight data and radar data (including every radar hit). Sample data were filtered by aircraft category (jet, or tuboprop, and props), airport, and operation (arrival, departure, or over flight) to reveal traffic patterns and flow interactions. Shared arrival and departure fixes were identified and viewed using PDARS in order to identify possible choke points or congestive flows. Different meteorological conditions, such as visual meteorological conditions (VMC), instrument meteorological conditions (IMC), and storm events, as well as runway configuration changes, were analyzed. Results were represented both in static and replay format indicating proximity of airports, airspace boundaries, crossing points and altitude assignments, arrival and departure transition areas (arrival and departure area, ATA and DTA, respectively), special-use airspace (SUA) and terrain, etc..

This knowledge sets up a framework for evaluating metroplex operational concepts. The observed practices to handle traffic interdependencies and coordination were abstracted into a temporal-spatial displacement concept. Existing NextGen concepts were carefully reviewed and compared against the temporal-spatial concept to identify the most relevant concepts, along with new concepts proposed to close any gaps in metroplex operations. The experiment strategy was developed to test the end effects of various concepts studied in lieu of modeling any specific concepts. Spatial and control parameters were then evaluated. It was determined that a Generic Metroplex experiment was to be employed to test various combinations of control parameters to identify the most promising concepts and capabilities for metroplex operations. Selected concepts were to be tested using SIMMOD models to verify the effectiveness of those concepts in a specific metroplex environment.

SIMMOD is a discrete-event simulation model that traces the movement of individual aircraft and simulated air-traffic-control (ATC) actions required to ensure aircraft operate within procedural rules. This tool computes capacity and aircraft delay-related metrics caused by a variety of inputs, including traffic demand and fleet mix, route structures (both in the airspace and on the airport surface), runway use configurations, separation rules and control procedures, aircraft performance characteristics, airspace sectorization, interactions among multiple airports, and weather conditions. SIMMOD uses a node-link structure to represent the airspace route structure and the surface system, including runways, taxiways, and gates.  Based upon a user-input scenario, SIMMOD tracks the movement of individual aircraft through an airport/airspace system, detects potential violations of separations and operating procedures, and simulates ATC actions required to resolve potential conflicts. The model properly captures the interactions within and between airspace and airport operations, including interactions among multiple neighboring airports.

The current-day airspace route structure was developed using radar flight track and flight plan data extracted from PDARS. The selected day (19 March 2007) represents typical visual-meteorological-conditions (VMC) flight operations in the N90 Metroplex. Four runway plan changes made during the day were included in the overall simulation model. However, because of the complexity of accounting for the dynamics of the plan changes in the temporal scheduling, only a single runway plan was utilized for the entire day.  The airports modeled in SIMMOD include the four primary N90 Metroplex airports: JFK, EWR, LGA, and TEB; and four secondary airports, including FRG, HPN, ISP, and SWF. When more than one arrival or departure runway was available, the distribution of runway operations was based upon the PDARS data.

The SIMMOD simulation revealed that, applied separately, both the NextGen fully decoupled airspace and the arrival scheduling significantly reduced arrival air delay incurred within the N90 terminal area; 28% and 60% system-wide reductions from current-day operations were realized, respectively. Combined, the decoupled airspace and scheduling reduced the system-wide arrival air delay from current-day operations by 79%. Consequently, fuel burn and emissions were also significantly reduced. The reductions from the NextGen decoupled airspace verified the hypothesis drawn from the Generic Metroplex linked queueing simulations. Results indicated that when entry fixes become major choke points, increasing the number of entry fixes and decoupled routes would improve system-wide performance. Scheduling showed a higher impact on system-wide delay reductions, similar to the results from the Generic Metroplex simulation.

In the SIMMOD simulation some issues were also identified. In the NextGen decoupled airspace, with the application of scheduling, the cumulative throughput for LGA runway 22 was below the throughput without scheduling during some busy periods, mainly because the scheduling algorithm intended to smooth out demand fluctuations at the entry fixes. In any case, this phenomenon warrants further study in the future. Another issue in the N90 NextGen decoupled airspace departure routes had longer ground tracks than that in the current airspace. Effort was taken to utilize improved departure profiles, but these improvements were limited and did not compensate for the impacts of longer ground tracks. Thus, the departure fuel burn was higher in the NextGen decoupled airspace than in the current airspace. Optimization could be employed to improve the NextGen decoupled airspace design to mitigate this effect.

Using ATAC’s tools and in-depth aviation knowledge, a significant range of metroplex issues and inefficiencies have been identified, a range of potential metroplex concepts have been analyzed, and significant potential benefits of metroplex concepts have been quantified.

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