Ligeia Paletti is currently a PhD student at the University of Patras, and works as a research associate at DLR Institute of Maintenance, Repair and Overhaul in the Product Lifecycle Management group. The focus of her research is the implementation of circular economy strategies in the air transport system and in aircraft design and operations in particular. Prior to DLR, Ligeia worked at NLR and in the aircraft industry. She graduated from the Politecnico di Milano in Aerospace Engineering. Her background (and professional interest) is in aerospace structures and materials, particularly in fatigue, damage tolerance and structural integrity. She is also connected to academia, having been a lecturer at Inholland University of Applied Sciences – faculty of Aeronautical Engineering (Delft-NL) (where she is still a member of the Advisory Board).

---

Q1: There is a lot of buzz about the transition to a sustainable aviation. But what does “sustainable aviation” mean?

Interestingly, there is no common definition within the aviation sector of what “sustainable aviation” means. In general, aviation is considered “sustainable” when its impact on the climate is minimal (ideally aiming to zero) impact on the climate. As the majority of climate impact of aviation occurs during flights, the sector has come to associate “sustainability” with CO2 emissions predominantly (though recently also of non-CO2 emissions or of GHG emissions). The “sustainability goals” set up by aviation organisations reflect this interpretation (the most famous of all being the ICAO Long Term Aspirational Goal of net-zero CO2 emission by 2050). 

But sustainability is much more than CO2 or GHG emissions; it touches upon societal aspects, biodiversity, labour conditions, and economic considerations as well. So, “sustainable aviation” is primarily narrowed to part of environmental sustainability, despite ACARE in Fly the Green Deal recognises the need to address the other pillars as well.

 

Q2: Why is there such discrepancy?

In my opinion, there is not one single reason. First of all, sustainability is a very complex topic in itself, and also a relatively “new” concept within the sector; no one was talking about it so openly 15 years ago and it was (and still is) not embedded in standard aviation education curricula. So, the sector is learning about sustainability while sustainability goals are being set and requiring to be met. 

Also, with the raising concerns regarding climate change, many sustainability-like concepts have been used in the past years/decades: green, environmental-friendly, net-zero, climate neutrality, circular economy, and so on. This has generated a lot of confusion in everyone, citizens and industry alike. So, from the aviation perspective, which is a very technically-based environment (also at high management- and strategy- level), I have the feeling that it has been straightforward to focus on the more “engineering-like”, so to say, parts of the sustainability concept, the quantifiable parts. 

Last, we need to keep in mind that sustainability is in itself a topic of research and that the science of climate change is still evolving rapidly. There is no doubt about the impact of human activities on the planet and on its climate, but what makes an impact, in what ways and with what entity is still researched. Accordingly, the targets are changing: from CO2 emissions towards including non-CO2 emissions; from in-flight emissions (as the largest contributor of aviation’s climate impact) and only towards including the full life-cycle.

Q3: You mentioned “Circular economy”, another topic which is frequently mentioned in connection with sustainability. What is it? And how is circular economy different from sustainability?

I start with what it is not: circular economy is not recycling, I wish to make this crystal clear. Circular economy provides an alternative to the current linear economy based on a “make-use-dispose” flow of products; this alternative model sees the end-of-life of a product as the beginning of the next life cycle and waste as the resources for new products. And to be able to “close the loop”, many aspects of how products are designed and used need to be rethought of. In simple words, circular economy is a means to sustainability, as other strategies can be, for example eco-design.

For an exact definition, I leave the stage to the experts at the Ellen Macarthur Foundation’s[1], whose website contains a lot of resources to learn about circular economy. 

Q4: How is circular economy applicable to the aviation sector?

The aviation sector is already acting according to various circular strategies, and without even being aware of this. For example, the aviation sector has made life extension of aircraft via repair and maintenance a fundamental brick of its modus operandi, both from a safety and from an economic perspective. But by keeping a product (the aircraft) in this case in service longer, there is less need for new products, which is a circular (and sustainable) practice. 

There are more examples of circular practices already in aviation (lightweight design, for example), but there are other circular economy strategies that could be applicable to aviation, for example a larger use of recycled materials or new business models (both for assets such as aircraft or aircraft components, and for airlines or airports).

Q5: Why aren’t more circular practices implemented in the sector?

I personally see two main reasons.

First of all, the lack of clear “engineering” definitions and of measurement and assessment methods for this “thing” called circular economy. As engineers and scientists, we love to measure. But measuring circular economy is not as straightforward as measuring fuel consumption or structural loads, and it has almost nothing to with assessing corporate sustainability (ESG or CSRD).  Beyond  the aviation sector, many methods and tools are being developed, but all have significant assumptions and limitations, and there seems not to be a standardized approach yet. Many experts use life cycle engineering methods to measure circular economy. Life cycle assessments (LCA) cover material and energy flows,  life cycle cost assessments (LCC) some economic aspects, but that’s far from providing a complete picture of circular economy. A more comprehensive tool to assess circular economy (and sustainability) is needed, whether by expanding LCA or by introducing something new. For example, the work done at the University of Patras towards a Sustainability Index.

The second reason is that aviation is used to operate with standards and regulations, and many current methods and tools have been well-established for a long time. Many solutions which could contribute to sustainability or circularity will require to go through an entire certification process or even have new regulations set up. As such processes can be extremely time consuming and expensive, without a clear idea of their potential impact (due to the lack of a measuring/assessment method), it will be difficult to get the process going.

Q6: In your opinion, what are the real challenges for the aviation sector towards becoming sustainable or circular?

Measuring methods for sustainability and circularity have been indicated as challenges by many of my colleagues, together with technologies, such as industrially implemented recycling processes. Both are truly challenging, but to me those are “normal” engineering problems, which will be solved, sooner rather than later. In my opinion, the real challenge is to change the mindset of the aviation community from trying to solve a complex problem as the transition to sustainability by technology only. What I mean with this is that “traffic of electric cars is still traffic”. I challenge anyone to prove that being stuck in traffic in an electric car is sustainable. A similar situation applies to the aviation sector, which is approaching the transition to sustainability as a matter of energy transition, and even looking at this in a very limited way. Talking about stop or slow (while technology catches up) the growth of aviation is not contemplated in the sector.

Also, despite all strategies for a sustainable aviation mention the need for a multidisciplinary approach and for involving all stakeholders, in practice that is limited to a technical multidisciplinary of aviation stakeholders. So, partnerships like those between Clean Aviation JU and the Clean Hydrogen JU are straightforward successful matches, but the involvement of citizens’ groups, sustainability experts or economists is limited to smaller initiatives, thus with less impact than necessary.

I dream that the sector would go back to the mindset of the heydays of aviation, when there was more experimentations and challenges to the status quo. This is partially happening, with the proliferation of start-ups developing new electric or hydrogen aircraft, beyond the traditional OEMs. Of course, the mindset should be open to real disruptive solutions without forgetting what the sector learnt in the meantime, especially with regard to safety. At the end, the sector and the society need to accept that to make aviation part of a truly sustainable mobility system will require more changes that we are willing to openly discuss now, more than energy transition or than technological advancements.