The Five Minute Feature: Sustainable Taxiing with EUROCONTROL and ACI EUROPE
How can aircraft reduce emissions during the taxiing phase – moving along the ground before take-off or after landing? ACI EUROPE’s Five Minute Feature this month addresses the concept of sustainable taxiing – referring to the practice of reducing or eliminating the use of aircraft engines during taxiing. Riding on the release of the EUROCONTROL and ACI EUROPE’s Concept of Operations and Industry Guidance, EUROCONTROL’s Pascal Hop and ACI EUROPE’s Eugene Leeman explore the current state of sustainable taxiing, the benefits it can provide, barriers to implementation and the exciting future awaiting sustainable taxiing.
There is no doubt that airports are proactively committed to addressing the environmental impact of air travel; with ACI EUROPE’s members committed to achieving Net Zero carbon emissions under their control by 2050. This will involve decarbonising every part of the airport ecosystem. Can you tell me more about what sustainable taxiing is in comparison to traditional taxiing operations?
Pascal Hop: Sustainable taxiing, compared to conventional taxiing, is aiming to reduce emissions compared to the use of conventional jet engines (which is traditionally what aircraft use during taxiing). Sustainable taxiing refers to any procedure that involves using less of these jet engines. The ultimate goal is to reduce emissions by taxiing without jet engines at all, as they are a very inefficient method of moving aircraft on the ground.
There are multiple options for this: the use of electric taxiing solutions is one option, but there are other methods such as single engine taxiing (a specific taxi procedure using only one power unit for twin-engine commercial air transport aircraft). Our focus is on electric taxiing, what are the requirements for its implementation, and what operational stakeholders need to take into consideration when doing so.
How does sustainable taxiing have the potential to significantly contribute to emission and pollution reduction? How do the different solutions for sustainable taxiing – on-board, on-ground, and hybrid solutions – differ in terms of environmental impact and efficiency?
Pascal Hop: What is the potential of sustainable taxiing solutions compared to the total potential emissions reductions for each flight? This is what we aimed to look at.
Several ongoing studies such as the SESAR ATM Master Plan already explore potential emission reduction analysis; giving figures in the region of a couple of hundreds of kg of CO2 saved per flight for short-term improvements. However, as part of the Sustainable Taxiing Taskforce, we have calculated that sustainable taxiing (all engines off), taking into account thermal stabilisation of the engines, can potentially also save up to hundreds of kg of CO2 or 40% of emissions compared to Single Engine taxiing. It is possible that sustainable taxiing could, as short-term improvement, even surpass efficiency improvements in ATM in terms of its carbon impact. Generally speaking, sustainable taxi operations can save about half of the fuel burn of traditional methods.
While each flight is unique – and there are all kinds of assumptions to take into account – it is clear that sustainable taxiing should be seriously considered as part of the overall carbon reduction package at airports.
Eugene Leeman: It should also be noted that sustainable taxiing is of great benefit for airports handling mainly short haul flights, as the shorter the flight, the larger percentage of emissions can be reduced by sustainable taxiing. Sustainable taxiing saves the same amount of CO2 regardless of how long the plane then flies for.
Sustainable taxiing has gone from being simply an innovative idea to having a fully-realised CONOPs – Concept of Operations and Industry Guidance – authored by yourselves. How far along are we in terms of implementation across airports, and do any major barriers remain?
Pascal Hop: Single engine taxiing is already being implemented across Europe. While the industry is busy exploring carbon reduction opportunities, sustainable taxiing with engines completely off is currently not being implemented on a wide scale. However, some pilot projects are ongoing across Europe in larger airports such as Paris CDG Airport, Amsterdam Airport Schiphol, and Brussels Airport.
The main barrier to implementation is that operational stakeholders need to fully understand what the impact of sustainable taxiing is at the local airport, from a technical and operational point of view but also from a business/financial point of view. Within the CONOPs, we explain that the implementation of sustainable taxiing is a collaborative effort of all operational stakeholders. It is, for instance, necessary to decide how to invest in the potential needed infrastructure: from a technical point of view, electricity needs to be available at the airport and such an investment may require the input of multiple parties. There are further recommendations within the CONOPs to address these challenges.
Eugene Leeman: It is also interesting to look at how challenges manifest for different stakeholders. For the airport itself, the question of who is going to pay for the required sustainable vehicles and whether it will affect airport capacity will be at the forefront of their planning. For air traffic control (ATC), they will question the complexity it will add to their operations – taxibots used for sustainable taxiing can be slower than traditional taxiing methods, and therefore, ATC will have to account for vehicles that run at a different speed when handling aircraft turnaround. For airlines, they will question whether they need to train pilots and inform ground handlers on what kind of taxiing their planes require. Airlines seek consistency in their operations and want to reduce their complexity; ideally not having to consider different procedures at different airports.
Pascal Hop: Standardisation, and as a following step harmonisation of procedures, will help to overcome these barriers. Through this CONOPs, we are trying to present the current state of sustainable taxiing so that the barriers for further integration can be explored. We hope that the CONOPs will be used by pilot projects, which will in turn provide useful information in order to harmonise operations in the future. Ultimately, the goal is for sustainable taxiing to be pervasive and standardised globally, so that a pilot coming from India has the same procedural expectations as a pilot from the US, or Europe. Our CONOPs tries to list the barriers in order to find solutions for as many as possible – now is the time to push for implementation, solve the identified issues and look towards certification bodies to ensure commonly agreed procedures and terminologies.
What are the anticipated impacts on airport ground infrastructure and taxiway layout, due to the implementation of sustainable technologies? Are new safety protocols required, or considerations for emergency situations when sustainable solutions are used – particularly in pushback or tow operations? Are new training programmes required for pilot and ground crews?
Eugene Leeman: In terms of infrastructure, we advise and recommend in the CONOPs to use as much of the infrastructure that is already available at airports. It is not necessarily a requirement for airports to implement an entirely new infrastructure to support sustainable taxiing. It is even possible to use different locations on the airfield to optimise capacity. For instance, at many airports with de-icing operations, there are de-icing pads very close to the departure runways. These serve as temporary parking spots for aircraft while de-icing takes place. In the warmer times of the year when de-icing does not take place, these spots could be used for coupling or de-coupling sustainable taxibots. It is therefore an optimisation of capacity and a reduction in emissions, all in one.
However, the impact of hybrid operations must be considered. Airports are unlikely to switch to 100% sustainable taxiing instantly. Therefore, during this transition period we will see a mix of vehicles and taxiing procedures – in practice, this means vehicles moving at different speeds, different procedures in the same airport, the need to find space for vehicles, all adding operational complexity. This, we have discovered, is a barrier for stakeholders saying yes to sustainable taxiing. If it was possible to switch to 100% sustainable procedures instantly, most stakeholders would say yes: it is the transitional period of complexity that currently puts doubt in stakeholder’s minds. However, through the CONOPs we have examined both the benefits and challenges of sustainable taxiing, and we urge stakeholders to explore it through this lens: while it may add a temporary period of operational complexity, it can also improve turnaround times, safety, and air quality. It is about finding a balance – what is important for each stakeholder?
Are there other benefits of sustainable taxiing, aside from emissions reduction – for instance, noise and air quality benefits? What has been observed or projected in terms of noise reduction, especially in densely populated areas near airports?
Pascal Hop: We’ve seen a number of additional benefits that can be attributed to sustainable taxiing. Starting up the engine later, which naturally happens with sustainable taxiing (as you use the engines solely for take-off/landing rather than moving the aircraft on the ground) can reduce noise and improve local air quality, especially at the apron area where a lot of ground operational staff are active. Amsterdam Airport Schiphol have already indicated that by the end of this decade, they want all operations surrounding the platform and gates to be electrified for this reason.
Eugene Leeman: Safety is also a major factor. The majority of ground crew are around the platform and gate area, and so by starting up engines as the aircraft approaches the departure runway – far away from where most people are – you see safety improvements. Sustainable taxiing may also speed up turnaround time, by delaying the start-up of the engine away from the most congested part of the airport (the gates). By pulling aircraft away from the busy gates and completing procedures in other locations, gate capacity is optimised and bottlenecks are potentially reduced. It may even be possible to anticipate capacity improvement through pushback time – as the entire pushback procedure is optimised through sustainable taxiing, explained further in the CONOPs document.
How do you foresee collaborative efforts among stakeholders, such as airports, airlines, and ground service providers, to ensure efficient adoption of sustainable taxiing?
Eugene Leeman: Sustainable taxiing is an investment: every party needs to fully understand what the procedures are and the impact it will have on their own operations. It is important to be honest about the advantages but to also address challenges. By listening to stakeholder concerns, and suggesting the improvements that will come with implementation, stakeholders are generally more open to new procedures altogether. This is one of the key objectives of the CONOPs: how to look at the different perspectives of stakeholders, so that they understand what it means for them.
How do sustainable taxiing initiatives align with the broader UN Sustainable Development Goals (SDGs) for aviation, particularly those focusing on climate action? What role does sustainable taxiing play in achieving the EU’s Green Deal target for a 90% reduction in aviation emissions by 2050?
Pascal Hop: Aviation is a hard-to-abate sector, and it is undeniable that a significant portion of aviation emissions are outside of the airport’s control. While significant emission reduction is expected from solutions such as the use of Sustainable Aviation Fuel, and from emission offsetting, it is important to initially focus on reducing emissions at the source as much as possible. Sustainable taxiing is one way in which airports can directly and proactively contribute to emissions reduction, particularly for very large aircraft, where hundreds of kg of fuel is used during taxiing.
How do you envision the evolution of sustainable taxiing technology over the next 5-10 years?
Pascal Hop: As mentioned earlier, the pilot projects will be trailblazers in our understanding of how to effectively implement sustainable taxiing on a global level. We hope that they share their experience so we can develop harmonised procedures based on their initial results.
In a way, we’re also looking further towards the future at zero emission aircraft – these will completely negate the need for sustainable taxiing at all. But until we have such aircraft, we’ll undoubtedly see a gradual extension of sustainable taxiing technologies and methodologies.
Eugene Leeman: We also expect to see sustainable taxiing manufacturers grow in both size and scale. Today, there are only a limited number of manufacturers in this sector. We anticipate that there will be more aircraft types certified as well as new technologies to be developed – giving more options to stakeholders, and ultimately driving further implementation.
