Airbus and SESAR partners are taking wake energy retrieval to the next level

Following Airbus’ success with its recent “fello’fly” wake energy assisted A350 flight demonstrations, the EU’s GEESE project within SESAR, led by Airbus, is now taking the concept big steps forward. By further developing the science, technology and processes, together with our industry partners, we could one day see airliners riding the buoyant wakes of others, reducing fuel and associated emissions.

Between 2019 and 2021 as part of its “fello’fly” experimental project, Airbus developed and flight-tested a concept known as “Wake Energy Retrieval”. Abbreviated as “WER”, the technique sees a pair of airliners flying in formation, allowing the trailing aircraft to benefit from the lift generated by the preceding aircraft’s vortices, reducing the thrust required from its engines.

The campaign culminated on the 9th of November 2021, with the first long-haul demonstration of WER flights in transatlantic airspace. It involved two A350s separated by around 1.2 nm (2.2 km) from each other, flying as a pair from Toulouse, France to Montreal, Canada. The subsequent analyses suggested that airlines could save between five and 10 percent of fuel per trip. 

The positive results caught the attention of the wider industry within Europe and also across the Atlantic. This has now led to the *SESAR-3 Joint Undertaking (SESAR JU) partners joining forces to further explore WER under a new dedicated industrial research project called GEESE. While this stands for: “Gain Environmental Efficiency by Saving Energy”, it is also a nod to the fact that flocks of geese use a similar technique when they migrate in formation, flying over long distances, while benefiting from each other’s wake energy.

International stakeholder collaboration

Led by Airbus, GEESE is a 10-million-euro project funded by the European Union’s ‘Horizon Europe’ initiative and industry. This has brought together a range of stakeholders, including Eurocontrol, DSNA, Air France, ON, Indra, ENAC, DLR, AirNav, Bulatsa, CIRA, UAB, Frequentis, Boeing, French Bee, NATS, Virgin Atlantic and Delta Air Lines. 

GEESE aims to map out how to enable and scale WER operations for both transatlantic and trans-continental flights throughout Europe. The project defines the necessary operational tasks for pilots adopting technology to automatically manage various WER positions – including flight management systems and new WER cockpit functions that capture and track the wake vortex. The campaign is also exploring a ‘pairing assistance’ system for dispatchers at airline operations control centres. Notably, airline partners will work together to update their flight plans to find suitable aircraft to pair, taking into account routing to rendezvous point and other considerations.

To this end, the project will run a series of simulations to validate the pairing procedures, involving Air France, French Bee, Delta and Virgin Atlantic airlines. It will also further investigate wake science, to advance the underlying concepts and consider the impact of formations. This includes defining the wake generated by the second aircraft in a pair, safe positioning behind the pair, and how to ensure the safety of surrounding traffic.

Three operational ‘work packages’ are being developed within GEESE:

“Enable Europe to North Atlantic WER Operations” will develop and refine the initial concept-of-operation (CONOPS), its safety assessment, analyse impacts on legacy systems, and develop simulations and trials to assess assumptions.

“Scaling-up the WER concept to continental Europe”, will provide operational solutions for the extension of WER operations within European domestic airspace.

The third facet to GEESE, the Wake Science work package, – will investigate non-CO2 potential benefits of formations.

Current status and next steps

Following SESAR’s project selection and funding grant preparation which took place towards the end of Q2 2023, GEESE was given the green light to commence its three-year execution phase.

“Today, one year into the project we are mainly working on the definition of the operational processes which will be needed for preparing the WER operations,” notes Laura Montironi, Vehicles Systems Architect, in Airbus Engineering.

“These processes will govern how the two aircraft will adapt their trajectories. We will develop these processes together with the airlines and the controllers, so they can perform the flight plan changes and any adaptations that will enable the aircraft to meet.”

“We have made good progress to agree with stakeholders on the processes, paving the way for planning and detailing all the validation activities which we’ll perform next year.”

“This year we also launched the safety assessments,” she adds. “So we are still currently in the paperwork phase, as the flights themselves are planned to start around the second half of 2025.”

During the flight trials to be operated by Air France, French Bee, Delta and Virgin, the respective paired aircraft will be positioned at different altitudes – in accordance with today’s normal ATM vertical separation minima requirements. This constraint is not an issue for the GEESE trials, since their aim is not to re-demonstrate the WER uplift flight-physics (which is already demonstrated under fello’fly), but rather to validate the processes needed for the aircraft to converge and meet as a pair, from a navigational perspective.

Regarding the aircraft types to perform the tests, Laura says: “We are still converging on defining these, and that depends on the airlines’ respective flight planning. For the transatlantic flights it depends on which aircraft they will use on those sectors at the time of the trials. For Airbus, A350 will most likely be our platform of choice, especially given that it’s a long-range aircraft whose avionics and navigation capabilities are of the very latest standard.”

Flight plan uploading flexibility an advantage

Although not a prerequisite per se, it would nevertheless be advantageous if aircraft would enable the pilot to upload the flight plan directly into the aircraft’s flight management system (FMS). This capability, which is already available in the A350, avoids the pilot having to make flight plan modifications by entering all information manually using the aircraft’s MCDU keypad.

Once uploaded into the FMS the new flight plan will be selectable as a ‘secondary flight plan’ option, while the original flight plan would remain in the FMS as the primary flight plan.

Operational scenarios

For actual real airline operations it is envisaged that the new flight plan would only be released and sent by the airlines operations centre (AOC) to the pilot following a consultation and coordination between the AOC and the ATC controllers – who would be impacted by any flight plan change. Moreover, this would be done as part of a CDM workflow, during which the respective ATM controllers would confirm whether or not they could accept changes – for example taking into account sector loading or airspace constraints. Only once the new flight plan is approved would the pilot be authorised to activate the secondary flight plan in the FMS.

Moreover, the fuel load would actually remain exactly as per the original flight plan. “The fuel loaded would not be impacted, as it will be based on the ‘no-WER’ scenario,” says Laura. “In fact, what we propose is that the respective airlines will not know if they will effectively constitute a pair. They will just declare their intention that their flight could be part of WER.”

Aircraft agnostic requirements

While the WER trials will be essentially ‘aircraft type agnostic’, Laura nevertheless advises on some general requirements at ‘aircraft level’. “For example, a function able to automatically position the ‘follower’ aircraft automatically behind the ‘leader’ aircraft and track its vortex. However, what we would not do is dictate how this capability or aircraft functionality should be implemented in a specific aircraft design and how the aircraft technology would accomplish it.”

Laura adds: “For Airbus, this is done separately by our engineering colleagues in fello’fly. For other aircraft OEMs it would be up to them how they would want to implement the technical features.”

“Nevertheless, in GEESE, we are discussing whether we can extend the scope of the trials to include the A330 and some Boeing aircraft. We don’t have huge operational constraints on the aircraft itself – WER operation is mainly a flight plan change, so we are under discussion with airlines to evaluate the concept with a large set of aircraft types.”

 *SESAR = Single European Sky ATM Research