Using trajectory-based operations to manage flights in real time

The trajectory-based operations validated by the ATC-TBO project give air traffic control the flexibility it needs to deal with the uncertainties that may arise during the tactical execution phase of a flight.

Historically, aircraft fly using what is called point-to-point routing, navigating between fixed ground-based beacons and rigid airways and requiring continuous air traffic control (ATC) interventions to manage spacing.

"Not only is fixed routing inefficient, it creates a high workload for controllers and increases fuelburn, emissions and airspace congestion," says Dan Ivanescu, SESAR ATC-TBO project manager at EUROCONTROL.

This is where trajectory based operations (TBO) come in.

As opposed to relying on fixed routes and successive tactical adjustments, TBO is built around a shared and regularly updated view of each flight's intended trajectory. As a result, it helps controllers and airspace users anticipate constraints and coordinate more efficient flight execution.

"Trajectory-based operations share the common plan - the data for a flight's trajectory - across all phases of flight," explains Ivanescu. "In doing so, it maximises the performance of air traffic across the network while satisfying the needs of airspace users for individual flights."

While TBO has the potential to improve predictability, increase airspace capacity, reduce aviation's environmental footprint, and make flights more efficient, it isn't something that ATC can simply 'switch on'. Instead, TBO must be built piece-by-piece across all phases of flight, starting with pre-departure and including both the strategic and tactical execution phases.

To advance the implementation of TBO in Europe, the SESAR Joint Undertaking is funding several projects, each of which is focused on developing and validating TBO procedures for a specific phase of flight.

The ATC-TBO project, for example, focuses on validating TBO to provide flexibility and to deal with uncertainties within the tactical execution phase of flight. Within this phase, the project is proposing new operational procedures for modifying an aircraft's trajectory - procedures that were validated via 21 exercises (mainly real-time simulations) conducted across operational and industry platforms.

ATC-TBO in action

To illustrate what these exercises look like in practice, Ivanescu describes how an aircraft currently flies between sectors, with each sector having a fixed flight plan. But what if an aircraft is flying in Sector A when an unplanned situation happens in Sector B that could impact the planned route, such as weather or congestion?

"Because the situation is in Sector B, it is the responsibility of that sector's ATC to amend the flight plan, which they can't do until the aircraft is in their sector and under their control," says Ivanescu. "But ATC isn't just building a new flight plan for one aircraft - they're doing it for every flight heading into their sector, which creates a substantial workload for the controller."

With the procedures proposed by the ATC-TBO project, ATC in Sector B doesn't have to wait until the aircraft arrives - they can make the necessary changes as soon as a situation presents itself and well before the aircraft enters their airspace.

The proposed new route is then sent to Sector A, where the aircraft is currently flying, at which point it is translated into a proposal for controller pilot datalink communication (CPDLC) clearance.

"By downlinking live airborne trajectory information through ADS-C/EPP and using it to enhance ground-based conflict detection, resolution and trajectory monitoring tools, controllers can build a more accurate picture of each flight's intended path and issue lateral or vertical CPDLC clearances with greater confidence," remarks Ivanescu.

Towards a more connected trajectory based operating environment

The ATC-TBO project only focused on the tactical execution phase of flight. But when these solutions are added to the work being done by other SESAR projects, the result will be a more connected trajectory-based operating environment, link planning, network management and tactical execution.

"While projects such as NETWORK TBO address trajectory synchronisation before departure and at the network level, ATC-TBO brings this into live operations by giving controllers the flexibility to manage uncertainty, revise agreed trajectories in flight, and make use of opportunities as they arise," concludes Ivanescu.

More about ATC-TBO