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  • Writer's pictureAndreas Hardeman

Supersonic Flight: An Existential Threat?

(Originally published on 30 August 2019)

Now here is a provocative thought: Imagine being able to cut flight times in half for people traveling to Davos, Google Camp or even just their next climate conference? Or: how many extra trees will Elton John have to plant if Harry and Meghan decide to fly supersonic on their next trip to Nice?

"Alright, not funny", you might think. But it nicely captures the climate conundrum of supersonic flight. How worried should we be about the additional fuel consumption of new supersonic transport jets (SSTs)?

Predictions are that over the next two decades, we could see up to 2,000 supersonic airliners plying the skies, serving over 500 mostly transoceanic routes. This prospect, now brought into sharp focus by recent US Government proposals to facilitate SST flight testing, has set off alarm bells in environmental circles in a major way.

Exactly how bad do experts believe the fuel economy of new SSTs will be? The old Concorde managed about 17 passenger-miles to the Imperial gallon, which is 16.7 liters/100 km per passenger (pkm). Compare this to an industry average today of around 3.5 liters/100 pkm and it becomes clear that the new crop of supersonic jets will have to improve on historical SST fuel efficiencies quite dramatically - by a factor of 4 to 5 - in order to keep up with the subsonic Joneses.

However, a widely reported paper by the same NGO that sponsored the research that accidentally uncovered the VW emissions scandal in 2015, is predicting that future SST designs will burn 5 to 7 times as much fuel per passenger as today’s latest subsonic aircraft types (e.g. the B787-9). 

This would seem to suggest that either their assumed future SST design performs worse than the 1960s technology Concorde and/or the subsonic aircraft used for comparison in their analysis performs massively better than today’s global average. On the face of it, neither of these two scenarios sounds plausible. So what is going on here?

The reality is that manufacturers, understandably, are quite reluctant to share commercially sensitive test and performance data of their new SST designs. At this stage, we therefore simply have no way of knowing what exactly the fuel performance of future SSTs will be. All we know is that they will have to meet international certification standards (yet to be developed) and public expectations (yet to be defined). Right now, any analysis, whether done by global regulators or local NGOs, inevitably relies on “paper planes” built on arbitrary assumptions.

Until real operational SST data becomes available, we can either rely on analysis that assumes the worst, thereby running the risk of misinforming the standard-setting process and the public debate - or we can reserve judgment confident in the knowledge that human ingenuity and our thirst for progress will find ways to deliver highly fuel efficient supersonic jets that require no excuse.


This is Part 3 in a mini-series of blog posts focusing on emerging air transportation technologies and their contribution to sustainable development.

About the author: Andreas Hardeman (The Hague, 1967) is an internationally experienced air transportation lawyer, sustainability expert and acclaimed aviation writer and commentator on current industry trends. Opinions in this blog are exclusively those of the author and do not necessarily reflect those of his business associates or clients. He can be contacted directly at

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