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Trajectory-Based Automation System

The primary purposes of the air traffic control system are to keep aircraft safely separated and to minimize delay. This system includes approximately 14,000 air traffic controllers in 3,000 air traffic control facilities across the Nation who are responsible for getting each flight to its destination safely and on time.

In today's air traffic control system, an air traffic controller maintains safe separation of aircraft in a single sector by visually scanning the controller radar display and looking for potential conflicts. A conflict is defined as a situation where two aircraft come close to violating safe separation criteria. In order to resolve a potential conflict, an air traffic controller provides clearance advisories to the pilot through radio communication.

See caption below for a description of this image.
This screenshot represents a controller radar display very similar to those currently in use by air traffic controllers. Each target on the display represents an aircraft and its flight data block. Under today's system, an air traffic controller is responsible for the aircraft within a single airspace sector's boundary, outlined here in blue. An air traffic controller maintains safe separation by visually scanning the sector looking for potential conflicts.

What is the problem?

During a typical day, up to 5000 aircraft fly in the National Airspace System at any given time and that number is expected to increase. Air traffic demand is projected to grow in the coming 20-25 years and experts don't believe that the current airspace system can support a substantial increase in air traffic. Several factors limit airspace capacity, including severe weather and high demand at major airports, but overwhelming controller workload is a major concern when it comes to maintaining safety.

What is NASA's solution?

The capacity limitations of today's air traffic control operations and the expected increase in air traffic demand are the primary motivation for NASA's research in trajectory-based automation. NASA is currently developing the Trajectory-Based Automation System (or TBAS), which will enable an increase in the number of aircraft a controller can safely manage. In addition to visually scanning a radar display for potential conflicts, an air traffic controller will be assisted by TBAS in automatically monitoring the traffic in the area. TBAS detects traffic conflicts and displays them to the controller. Because TBAS supports multiple levels of automation, conflict resolutions may be generated manually by the controller or automatically by the system, and then transmitted to the aircraft using data-link communications. By eliminating some of the manual work that a controller traditionally performs, TBAS allows the controller to manage a larger volume of airspace containing higher densities of aircraft. In addition to identifying and resolving conflicts, TBAS responds to pilot requests for preferred routes and provides support to air traffic controllers for off-nominal situations.

See caption below for a description of this image.
The Trajectory-Based Automation System consists of two independent aircraft separation algorithms, strategic and tactical, to ensure safety. Both algorithms depend on a database of conflict-free aircraft trajectories that are communicated to advanced aircraft by data-link communications and to legacy aircraft using radio-based voice communications; the controller coordinates all of this activity.

TBAS analyzes the four-dimensional (or 4D) trajectories of aircraft in order to track their flight paths. A 4D trajectory is a prediction of an aircraft's latitude, longitude, and altitude as a function of time. Four key pieces of information are combined in order to generate a 4D flight trajectory for all aircraft in the sky:
  • Position and velocity data from radar or GPS
  • Filed flight plan information and flight plan updates
  • Wind and weather predictions from the National Weather Service
  • Aircraft performance models
Once 4D trajectories for all of the aircraft in the airspace have been determined, TBAS can compare the trajectories against each other to identify potential conflicts. When a conflict is detected, it needs to be solved without creating other new conflicts. TBAS dynamically generates a new horizontal or vertical trajectory for one of the conflicting aircraft, tests the new trajectory for conflicts with all other aircraft and repeats the process until an efficient, conflict-free trajectory is found.

See caption below for a description of this image.
This screenshot represents a controller radar display using TBAS. Here, TBAS automatically monitors the traffic in a multi-sector area and displays potential conflicts to the controller in a conflict list; the geometry of one of those conflicts is shown in red The automation suggests a resolution of the conflict to the controller, shown as a “trial plan” (in yellow) that the controller can modify if necessary by clicking and dragging the triangular waypoints. The final trajectory change is automatically composed as a data-link message and transmitted to the aircraft for execution with a press of a button by the controller. The reduced workload required to detect, analyze, resolve and communicate the trajectory change increases both airspace capacity and safety.

NASA conducts human-in-the-loop simulations to test the performance of TBAS in real-world traffic conditions. Various scenarios are tested using actual traffic and flight plan data from the Federal Aviation Administration (FAA). Traffic flow and aircraft separation characteristics are measured during the runs, and then compared to those of today's operations. Past simulation runs included conditions where a single controller maintained safe separation and improved flying time efficiency by up to 5.2% for the combined traffic of five Fort Worth Center sectors under normal traffic levels. Under these simulation conditions, the controller performed the safe separation functions usually performed by 4-10 controllers under today's operations. Simulation results show that the use of TBAS has the potential to help accommodate the growing demand of the air traffic system without sacrificing safety.

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Automated Conflict Resolution
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Photo of Dave McNally presenting at the Aeronautics Technical Seminar on January 16, 2007.
Concept and Laboratory Analysis of Trajectory-Based Automation for Separation Assurance in the National Airspace System
Aeronautics Technical Seminar Series presented by Dave McNally.
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October 26, 2011
Successful Test of En Route Trajectory Automation Integrated with Today's Data Comm and En Route Automation Modernization
Two-way air/ground data-link communication (data comm) using today's actual data comm network (ARINC) and actual Boeing 777 flight hardware was demonstrated using NASA ground-based trajectory automation from the Center/TRACON Automation System (CTAS) at Ames and a B777 simulator equipped with integrated Flight Management System (FMS)/data comm at Boeing in Seattle, Washington.
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September 14, 2011
Successful Simulation with Controllers and Pilots in the Loop Demonstrates Viability of Efficient New Weather-Avoidance Routing Capability
On September 2, 2011, the “Trajectory-Based Automation System for En Route and Transition Airspace” (TBAS-ET) project successfully completed a two-week simulation evaluation with controllers and pilots in the loop.
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May 25, 2011
New Ground-Based Capability Prototyped that Dynamically Finds Time-Saving Weather Avoidance Routes
A new function that automatically finds alternative convective weather routes that save time and fuel for en-route aircraft has been implemented in the Center/TRACON Automation System (CTAS).
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March 2, 2011
Integration of CTAS, FANS-1/A Data Comm, and ERAM for Operational Trials
Technical meetings with representatives from NASA, Boeing, and Lockheed Martin were held on February 9-10 and February 22-23, 2011 at NASA Ames Research Center.
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"A Near-Term Concept for Trajectory-Based Operations With Air/Ground Data Link Communication,"
McNally, D., Mueller, E., Thipphavong, D., Paielli, R., Cheng, J., Lee, C., Sahlman, S., and Walton, J., 27th International Congres of the Aeronautical Sciencs (ICAS), Nice, France, 19-24 Sep. 2010.
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"Automated Separation Assurance in the Presence of Uncertainty,"
McNally, D., and Thipphavong, D., International Council for the Aeronautical Sciences (ICAS) 2008 Congress, Anchorage, AK, 14-19 Sep. 2008.
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"Experimental Evaluation of an Integrated Datalink and Automation-Based Strategic Trajectory Concept,"
Mueller, E., AIAA-2007-7777, 7th AIAA Aviation Technology, Integration and Operations (ATIO) Conference, Belfast, Northern Ireland, 18-20 Sep. 2007.
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“Concept and Laboratory Analysis of Trajectory-Based Automation for Separation Assurance”
McNally, D., and Gong, C., Air Traffic Control Quarterly, Vol. 15(1), pp. 35-63, 2007.
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NASA Fact Sheet
Download the NASA Fact Sheet on TBAS.
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