First Steps

Flight Simulation

Dave Hughes reports on how the United States’ NextGen programme is transitioning towards Trajectory Based Operations

Now that the NextGen system, Terminal Flight Data Management (TFDM), is in development and deployment, the NextGen time-based management infrastructure is nearly complete. This is allowing the Federal Aviation Administration (FAA) to focus on making the National Airspace System (NAS) a fully time-based rather than a miles-in-trail enterprise.

Time-based management as a key principle of Trajectory Based Operations (TBO) wouldn’t be possible without this past decade of NextGen progress. TBO integrates the significant NextGen investments made in Performance Based Navigation (PBN), surveillance, communications, and automation systems for decision support, flight-data management and information sharing.

TBO involves strategically planning, managing, and optimising flights throughout the operation by using time-based management, information exchange between air and ground systems, and the aircraft’s ability to fly precise paths in time and space using PBN procedures.

Together, time-based management and PBN comprise a 4-D trajectory – the 3D flight path plus time – that will be used by aircraft operators and the FAA to manage routeings. There will be more precise estimates than are currently in use for crossing-times at key points from gate to gate.

The FAA is working toward a PBN-centric NAS and has created a nationwide network of PBN arrivals, approaches, departures, and low- and high-altitude routes that are delivering benefits across the NAS. PBN reduces flying time, cuts fuel burn and emissions, and improves the efficiency and predictability of departures and arrivals and enhances safety as aircraft fly more stable arrivals and departures. TBO will facilitate more effective use of PBN with improved traffic sequencing and spacing so aircraft can stay on track from start to finish during a procedure.

The time parameter provides a common planning reference across all phases of flight, including pre-departure. The trajectory facilitates air traffic management across air traffic control (ATC) domains, enables the FAA to make plans that take user objectives into account, and allows for a more collaborative solution for each specific flight, based on air traffic and weather constraints. This represents a great improvement over today’s strategic-planning initiatives and tactical-flow management techniques, and addresses many of today’s operational shortfalls.

The NextGen Stage is Set for Initial TBO in 2020

The PBN-centric NAS is just a part of the FAA’s efforts to modernise communications, navigation, surveillance and information exchange capability in the NAS that is well on its way to completion. These innovations include Data Communications, Automatic Dependent Surveillance Broadcast, PBN, upgraded and new decision support systems, System Wide Information Management, new aviation weather capabilities and other improvements.

All the FAA’s air traffic control automation platforms support NextGen time-based management. While the first two listed below were started in development before NextGen began, the three incorporate NextGen capabilities that support more tightly coupled strategic and tactical operations through predominant use of time-based management. These include:

  • En Route Automation Modernisation (ERAM) in use at 20 FAA en route centres nationwide. ERAM replaced the 40-year-old En Route Host computer and backup system in 2015.
  • The Standard Terminal Automation Replacement System (STARS) is a single, state-of-the-art platform that is being installed at terminal radar approach control (TRACON) facilities and towers nationwide. STARS is already operating at the 11 largest TRACONS in the United States. The FAA, in partnership with the Department of Defense, will have STARS operating by 2019 at all 255 civil and military TRACONs and over 500 air traffic control towers in the NAS.
  • Terminal Flight Data Manager (TFDM), the FAA’s new surface-management solution now in development, includes electronic flight strips and a variety of surface-management decision support tools to more efficiently manage delays and utilise runway capacity. The FAA has scheduled initial TFDM deployments in 2019. Leidos is developing the system under a NextGen contract with the agency.

The FAA also is working closely with NASA to pave the way for TFDM’s full success by exercising TFDM’s planned decision capabilities in the prototype surface-management technology developed in the Airspace Technology Demonstration 2 (ATD-2) project NASA is conducting for departure metering at Charlotte Douglas International Airport.

ATD-2 surface management automation developed by NASA follows the TFDM system specifications. TFDM also will be linked to two systems already used by the FAA: Traffic Based Flow Management (TBFM) and the Traffic Flow Management System (TFMS). TBFM is the technology used to adjust capacity and demand imbalances at departure fixes and other waypoints across the NAS. TFMS is a suite of automation tools used for traffic management planning and to implement actions needed to adjust demand to match available capacity. Both TBFM and TFMS will play a role in supporting TBO in the NAS.

The Transition to TBO

The NAS will transition to TBO gradually. Different levels of capability will be employed based on local needs, with the highest level of capability going to the nation’s largest hub airports and busiest terminal airspace. While TBO will be used throughout the NAS, covering all IFR operations in controlled airspace, higher levels of performance will be applied by the FAA when and where they are needed.

TBO will be applied in the NAS based on a variety of inputs and existing conditions. Key among the inputs will be daily air traffic management operational goals, air traffic demand between city pairs, the airspace involved and aircraft equipage. In collaboration with air carriers, the FAA will take into account routing requests based on their business cases.

The strategic entry level for TBO will include a planned departure schedule and flight plan – more or less what aircraft operators are already working with today. Beyond that, aircraft operators may participate more fully by providing additional data and flight preferences. Ground automation will use the data provided to calculate crossing time and altitude estimates as needed along the planned route. FAA air traffic management will orchestrate all the trajectories.

In high-density airspace where time-based management techniques are needed, TBO tools will be used at all times, even when traffic demand does not exceed capacity and no controller or pilot action is needed to meet the plan’s objectives. This is essential to sustain operational predictability and assure the regional/national strategic plan is maintained. Changes can be made and approved to accommodate requests from aircraft operators as part of the overall strategic plan. This will replace ad hoc actions taken in isolation within an individual sector – as is often the case today.

Controllers remain responsible for separation assurance. The improved synergy between strategic and near-tactical planning should decrease the complexity of conflicts that controllers need to resolve tactically, because expected flight trajectory interactions will be better understood. It is not the goal that planned trajectories be free of traffic conflicts as that objective would unduly constrain operations and limit the use of capacity. Controllers will continue to tactically resolve any conflicts and the planned trajectory will be updated, if needed, to account for the impact of the conflict resolution.

TBO solutions will be introduced across the NAS as part of an integrated plan driven by an NAS-wide implementation strategy. The FAA will ensure that all new ground-automation capabilities, PBN routes or procedures, operating agreements, ATC procedures and training, and aircraft equipage levels are ready for a smooth transition to operations in a given location. The FAA expects the experience gained from rollouts from one region to the next to enable it to increase the operational benefits of TBO as it moves toward nationwide implementation.

The FAA plans to continue its collaboration with the user community to further develop and validate advanced TBO concepts of operation. There is still work to be done to develop mature requirements so that advanced TBO can be implemented.

The Next Step for TBO

The FAA is aiming to complete a step toward full TBO by 2025. The goal is to improve air traffic management strategic planning and to make time-based management predominant, while using precise and repeatable paths defined by PBN procedures and routings.

TBO in 2025 will depend on the use of improved data sets and greater collaboration between the agency and aircraft operators to enable better traffic planning and scheduling decisions. This will be supported by access to new data elements, more accurate and timely data, and data integrated into automation tools where appropriate.

Aircraft operator data and requests will be considered by the FAA when generating air traffic schedules. TBO in 2025 also will depend on providing controllers, traffic managers, and airspace users with the necessary decision-support tools to provide efficient flows that meet that schedule and the ability to adapt to changing operational conditions. It also requires that aircraft be appropriately equipped with navigation and communication capabilities needed to achieve the full benefits of TBO.

Improvements made with TBO by 2025 will advance aviation in an environmentally responsible and energy-efficient manner. Simultaneously, we will move from an almost entirely cognitive-based aviation control system to a collaborative work environment with automated support for decisions. Advanced TBO operations will be implemented in the years to follow.

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