AoC number


Primary domain


Secondary domain



This concept also known as Trajectory Based Operations (TBO) will provide the capabilities, decision-support tools, and automation to manage aircraft movement by trajectory. It will enable aircraft to fly negotiated flight paths necessary for full Performance Based Navigation (PBN), taking both operator preferences and optimal airspace system performance into consideration. TBO is a cornerstone of NextGen and SESAR; it is a major operational transformation for aviation, basing safe separation on much higher levels of automation that assesses the current aircraft positions, with respect to their future positions in time. TBO is a 2025 air traffic management system concept that manages aircraft through their Four-Dimensional Trajectory (4DT), gate to gate, both strategically and tactically to control surface and airborne operations. A 4DT includes a series of points from departure to arrival representing the aircraft’s path in four dimensions: lateral (latitude and longitude), vertical (altitude), and time. 4DTs will be used for planning, sequencing, spacing, and separation based on the aircrafts’ current and future positions. Separation duties will be performed by a combination of airborne and Ground Based Automation (GBA).

Historical perspective: On clearance-based ATC… and the drivers/enablers for TBO.

These functions integrate the traditional functions of navigation (defining a path and creating path guidance) and flight control (steering the aircraft to that path). It adds additional capabilities for NextGen, including conformance monitoring, trajectory negotiation (a traditional “communication” function), and some functions to support trajectory planning (weather data, traffic data, fuel optimization, etc). Strategic trajectory planning, or trajectory optimization (to optimize time or fuel within a given set of constraints such as aircraft performance and weather), may take place within the aircraft trajectory management function or may be accomplished in a ground system and the result communicated to the aircraft. A common operational concept of use for mid-term Tops is in development through RTCA, and a parallel activity in JPDo is defining the long-term Tops capabilities.

Potential hazard

  1. Synchronous garble and False Replies Unsynchronized In Time preventing CPDLC messages from getting through.
  2. ADS-B ground system failure; ground based automation does not receive ADS-B message
  3. Inaccurate modeling of wake location and strength (drift, sink, persistence, severity)
  4. Ground based conflict resolution not calculated. With increasing levels of traffic, TCAS may not provide a robust defense.
  5. Safety critical input data are incorrect, late or missing
  6. Software processes are too slow to reliably fulfill the automation requirements
  7. Breakout maneuvers, go-arounds, or missed approaches are not conflict free
  8. Controller misunderstands what the automation is doing with other aircraft in his/her sector
  9. Excessive controller workload due to TBO complexity
  10. Excessive controller workload due to TBO automation failure
  11. Pilot distractions: pilot makes mistakes when performing TBO navigation due to distractions from TBO related distractions (conformance alerts, etc.) in cockpit. This distraction may become more likely, when the instruction requires the pilot to involve ‘knowledge based behavior’ (Rasmussen, 1983). This follows from very recent NLR research into improved angle of attack indications, where a ‘Rule Based Isomorphic’ display had the best results during stressful situations.
  12. Pilot performs traffic avoidance maneuver to clear aircraft not accounted for in the current 4D trajectory
  13. Pilot performs weather avoidance maneuver not accounted for in the current 4D trajectory
  14. Pilot decision making when presented with weather information may not be uniform.
  15. Aircraft emergency situations (off-nominal); aircraft has an emergency and must deviate from 4D trajectory
  16. Missed approach under TOB; unanticipated change to the 4D trajectory by the aircraft
  17. Received information from GPS incorrect or missing
  18. Unmanned Aircraft loses control link and is not visible to ground based automation/ANSP, Unmanned Aircraft is executing the predetermined flight plan from the point it lost link.
  19. Control link failure between UAS and ground station; equipment failure; intentional takeover
  20. Unauthorized aircraft or vehicle traffic; aircraft or vehicles not equipped with transponder or ADS-B

Corroborating sources and comments

2014 – Performance-based navigation. Area navigation based on performance requirements for aircraft operating along an

ATS route, on an instrument approach procedure or in a designated airspace. Note: Performance requirements are expressed in navigation specifications in terms of accuracy, integrity, continuity, availability and functionality needed for the proposed operation in the context of a particular airspace concept. Trajectory Based Operations (TBO) represents a shift from clearance-based to trajectory-based control. Aircraft will fly negotiated trajectories and air traffic control moves to trajectory management.

The roles of pilots/controllers will evolve due to the increase in automation support. The focus of TBO is primarily en route cruise. Adaptive increased glideslope (3 to 4.5 degrees).

June 2013 FAA NextGen Implementation Plan:

As of February 2013, the FAA had installed 445 operational ADS-B ground stations. These will provide separation services at 28 Terminal Radar Approach Control (TRACON) facilities.

The FAA will take advantage of increased surveillance and navigation accuracy, as well as an improved understanding of wake vortices, to allow aircraft to operate simultaneously, either independently or with reduced separation, on closely spaced parallel runways. Key near-term schedule dates for Aircraft Operator Enablers:

Performance Based Navigation (PBN)

2014 – Advanced RNP, RNP 0.3, RNP 2

2015 – Trajectory Operations Navigation

2018 – Alternative Positioning, Navigation, and Timing

Capability Safety Assessment of Trajectory Based Operations, December 21, 2011, Joint Planning and Development Office (JPDO) Trajectory Based Operations (TBO) Capability Safety Assessment (CapSA) Team

The EU-funded FLYSAFE project brought together the research and simulations of the coming new ATM technology. The project was set up to improve the safety of air travel by providing crews with better information on the three most common external threats for aircraft – weather conditions, traffic collision and terrain collision. FLYSAFE looked at the design, development, implementation, testing and validation of a ‘Next Generation Integrated Surveillance System’ (NG ISS).

A key development is a Weather Information Management Systems (WIMS) to gather much more detailed and accurate information on upcoming weather conditions than current systems. This means pilots will be better warned about potentially dangerous situations such as Clear Air Turbulence (CAT), thunderstorms and icing – conditions which current aircraft weather radar. FLYSAFE utilized a multidisciplinary team to produce useful results.

FAA AVS Workplan for NextGen 2012, P. 37

OI 104120 Point In Space Metering: Air Navigation Service Provider (ANSP) uses scheduling tools and trajectory-based operations to assure smooth flow of traffic and increase the efficient use of airspace.

OI 104117 Improved Management of Arrivals/Surface/Departure Flow Operations (IASDF): This OI integrates advanced arrival/departure flow management with advanced surface operation functions to improve overall airport capacity and efficiency. ANSP automation uses arrival and departure scheduling tools and four-dimensional trajectory agreements to flow traffic at high-density airports. Automation incorporates Traffic Management Initiatives (TMIs), current and forecasted conditions (e.g., weather), airport configuration, user-provided gate assignments, requested runway, aircraft wake characteristics, and flight performance profiles. ANSP, flight planners, and airport operators monitor airport operational efficiency and make collaborative real-time adjustments to schedules and sequencing of aircraft to optimize throughput.

OI 104115 Current Tactical Management of Flow in the en Route for Arrivals/ Departures: Proper spacing and sequencing of air traffic maximizes NAS efficiency and capacity in the arrival and departure phases of flight. Controllers provide traffic synchronization to aircraft by monitoring the situation, making control decisions, and modifying flight trajectories to meet operational objectives and accommodate user preferences. They achieve this by applying manual controller optimization procedures. Traffic specialists and controllers use traffic displays (radar and enhanced traffic management system) and flight strips to establish flow initiatives, such as assignment to alternative arrival flows or miles-in-trial requirements.

Eurocontrol TBA1 (starting ~2015) & TBO 2: Performance-based Operations (starting ~2018) will rely on Network Management, new airport infrastructure, information management, Traffic Manager and supporting automation. SESAR – Overall Framework and Concept, Bob Graham, Eurocontrol, Collaborative Network Design.

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