In his sustainable aviation course, aerospace engineering professor Phil Ansell asked, “What does sustainability look like integrated to a system engineering process?” One of his student’s answer became a new definition of sustainable aviation and a framework for achieving it.

“Industry, government, and academics have stated sustainability goals, but at times the goals contradict each other. We don't even know how to achieve some of the goals. What we do know is system engineering—a process for designing complex systems," said Elias Waddington, Ph.D. student in The Grainger College of Engineering, University of Illinois Urbana-Champaign.

“I believe we must look at the challenge holistically– everything, all at once—because sustainable aviation isn’t just an environmental issue. If it were, we could just stop flying. Problem solved. But that solution doesn’t serve our needs for transportation and commerce.”

Waddington and Ansell ultimately developed a definition of sustainable aviation that is all-encompassing. It examines sustainable aviation as a process that connects communities and mobilizes people, goods, and services—all while minimizing negative impacts on human health, fostering a productive quality of life, and conserving natural resources.

“We can’t ignore any element. We need to look at how aircraft affect the world, and we need ways to measure those effects,” Waddington said.

This new definition of sustainable aviation creates a way to describe aircraft.

“One example is the Concorde. It was certified, built, flown, and put into service. But it was prohibitively expensive to operate, leading to commercial failure. That alone indicates it was unsustainable. In addition, the high cost limited the social impact it had, not to mention the relatively high environmental impact for the relatively few passengers who flew on it.”

To begin the process of quantifying the sustainability of an aircraft, Waddington created a framework in which he assigned numerical values to assess vehicle system and operational performance in categories such as technology readiness, operational cost, end-of-life recyclability, and certifiability.

“In terms of technology readiness, think of a 10-point scale. If we understand the basic physics, an aircraft design gets a one. Three means we can run the critical aircraft technologies only in the laboratory. Four through six means we've done it at scale and flown it at altitude. A score of 10, means it’s actively in service with flight-proven hardware. For example, the A320 is a 10. The Airbus ZEROe is rated low on technology readiness, not because it doesn’t show promise, but because it’s still experimental. Significant technological developments will have to occur before the ZEROe can fly.

“This framework is meant to show what our perspective on sustainability can do for the analysis of future aircraft. We can look at a design and say it has great environmental potential, but we have a lot of technical and policy challenges associated with it.”

Waddington credits Paul James’s book Urban Sustainability in Theory and Practice: Circles of Sustainability for helping him develop the framework.

“I was trying to conceptualize ways to represent and communicate sustainability when I stumbled upon one of his diagrams. When I read James’ book, I thought, here’s someone who's thought a lot about complex human systems, that interface with all these different societal and planetary elements. James measured cities. I adapted his model for aviation.

At this stage, Waddington said it is a way to think about and communicate sustainability, but the details of this analysis are preliminary. He said they are working on measuring the sustainability effects of historical and contemporary aircraft.
“Sustainability is like safety,” Waddington said. “It is not something you can just check a box and be done with. It's a process in the way that we think and interact with the world–and can thrive when adopted as a culture.”

The study, “A definition, conceptual framework, and pathway towards sustainable aviation,” by Elias Waddington and Phillip Ansell is published in the journal Progress of Aerospace Science. DOI: 10.1016/j.paerosci.2024.101050