INCREASING NAS CAPACITY

Collaborative air traffic management

New concepts to control and distance aircraft are being implemented. Cockpit-managed separation trials may portend future development for autonomous airspace control.

By Bill Gunn
ATP/CFII.
Pro Pilot Regulations and Compliance Specialist


New air traffic control tower at LAS (McCarran Intl Airport, Las Vegas NV) was open for business a year ago on August 28. One of the top 10 busiest US airports, controllers handle well over 500,000 flights with 45 million passengers per year.

Today's radar and other ground based systems for traffic separation are at or beyond capacity, particularly for arrival and departures to and from high density traffic airports. At best, gate hold, miles-in-trail, and a host of traditional methods to sequence and separate traffic only work up to reasonable traffic levels. Several new concepts for traffic management in the national airspace system (NAS) are designed to increase efficiency and capacity while maintaining acceptable levels of safety.

Legacy spacing

Miles-in-trail with metering via waypoint crossing has been used for many years for high density airspace. This requires controllers to make adjustments typically by using vectors. Speed adjustment methods required coordination among ATC facilities to prevent a chain of dominoes effect for following traffic and often were ineffective for immediate spacing requirements.

Traffic management advisor (TMA) is an air route traffic control center decision-making tool that calculates the number of aircraft TRACON can handle for a set period of time. Multicenter TMA shares information with adjoining Centers. Additional center programs consider aircraft performance, weather effects, and airspace limits to permit engine start and departure times with predicted arrivals.

Because many of these programs are not integrated and the capacity of the programs is near limits, delays often result. Los Angeles Center changed from miles-in-trail to time-based metering in 2002. This produced an improvement but still showed that the complexities of the airspace required large scale integration if additional gains were to be realized.

The FAA uses 3 decision-supporting systems in an attempt to integrate air traffic: Time Based Flow Management (TBFM), Traffic Flow Management System (TFMS), and Terminal Flight Data Manager (TFDM).

Time Based Flow Management

Collaborative air traffic management is flow management based on time and rerouting to improve traffic flow. From the initial change for LA Center, time metering as the basis for traffic separation prediction is becoming the norm and is currently used at 28 core airports such as ATL, JFK, LAX, and DFW, as well as 13 airports not considered core, such as CLE, DAL and HOU. Software updates to existing programs were made in 2016 with further software upgrades planned through 2018.

Considering a flight profile as composed of taxi and departure, climb and enroute, and descent and arrival, select programs are introduced for each route and airport environment. At departure point, route clearance plus taxi and departure slots are issued to place the aircraft into the enroute stream in an optimal manner. The concept is then to establish an accurate crossing time at key points up to an hour before the aircraft arrives at destination, primarily using speed adjustment to maintain time based separation.

An RNAV optimized profile descent (OPD) aims to reduce step-descents and permit operation at or near flight idle power with minimal throttle changes. The arriving aircraft spends a larger part of its overall flight time at more fuel-efficient cruise altitudes before initiating the descent to destination. While step-descents may still be required for merging and sequencing, OPDs can reduce the time aircraft spend in level flight at intermediate altitudes and shift them to higher, more fuel efficient altitudes.

As part of the TFMS, TRACON controllers receive the scheduled location/height/times of arrival on their displays. They then guide the flights so that each aircraft reaches its intermediate waypoints at the right time while maintaining the required separation between them using time-based metering. Implementation is tailored to specific airspace sets using proximity of ATC boundaries, known weather patterns, limitations of runway environments, and a host of other factors making each operation unique.

This TFMS is incorporated at 82 air traffic management sites. TFMS is used locally as a stand-alone tactical tool or strategically when used to balance capacity across multiple ATC facilities. Tools include adoptive compression to maximize slot use when ground delay is in place, re-routing impact assessment to model in advance the effect of re-routing, weather integration for flow decision making, and trajectory options providing a range of re-routing options for each flight based on all available factors, plus many other tools necessary for each terminal environment.

Information is key

Aircraft sequencing using time rather than distance is a core piece of the FAA's NextGen System. The use of TBFM in conjunction with performance based navigation, another key element of NextGen, should greatly increase the capacity and efficiency of the NAS.

Any program designed for efficient traffic flow is only as strong as the most limiting element. Innovations to provide the right amount of information to the right location at exactly the right time are critical to success. An excellent example of placing information where it makes a difference is the system-wide information management visualization tool (SVT) now in use at the Southern California, Northern California, New York, Potomac, Chicago, Boston, Houston, and Louisville TRACONs, as well as Los Angeles and New York Centers and the Air Traffic Control System Command Center.

SVT presents real time surface traffic information to controllers that was typically previously only available to tower. Using the surface ASDE-X and ASSC tracking systems, controllers can integrate the advisories provided by SVT into their decision making. Color coding by departure fix assigned to the aircraft permits controllers to more exactly predict how busy a particular route will be and when.

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