Speaking to journalist Laura Kuenssberg on Sunday (26 January), chancellor Rachel Reeves was repeatedly pressed on speculation around an announcement about a third runway, which was finally made today (29 January). The expansion is seen as a potential boost for the government’s growth mission, but there are widespread concerns around increased pollution and disruption to people under the airport’s flight paths.
Asked about London mayor Sadiq Khan’s comments that the decision could have a damaging impact on air quality, noise and London’s ability to achieve net zero, Reeves said that “a lot has changed in terms of aviation.”
“Sustainable aviation fuel (SAF) is changing carbon emissions from flying. There's huge investment going on electric planes, and also a third runway will mean that, instead of circling London, flights can land at Heathrow. So a lot has changed in aviation, and sustainable aviation and economic growth go hand in hand,” she said.
“I believe that clean energy [and] reducing our carbon emissions are good for economic growth. We can do the two together.”
SAF and electric planes offer potential opportunities to cut some emissions. Both technologies are at a relatively early stage, however, and experts told Professional Engineering that any benefits are “far down the line” and unlikely to be available for several decades – longer than a potential 10-year timeframe for a new runway.
“The first rule of aerospace is nothing happens quickly,” said Steve Wright, former lecturer and researcher in aerospace engineering at the University of the West of England.
There has already been some small introduction of the new fuels, which can be blended with fossil fuels – the SAF mandate introduced this month requires at least 2% of fuel used to be SAF this year, rising to 10% in 2030 and 22% in 2040. Last year, it accounted for 0.3% of global jet fuel production, according to the International Air Transport Association.
SAF is a “long way from having a considerable impact on carbon emissions,” said Sebastian Eastham, senior lecturer in sustainable aviation in the department of aeronautics at Imperial College London. A “co-design problem” needs to be solved, he said – engines must be designed to work with 100% SAF, and 100% SAF must be designed to work with the engines.
“You could not, for example, replace all of the fuel in Heathrow's tanks today and expect things to go smoothly,” Eastham said. “Considering that most passenger aircraft last about 25 to 30 years, you have a legacy of aircraft, which are not currently capable of running with current SAF.”
Scaling up production is also “incredibly hard”, he added. “We are talking about trying to keep aviation cheap, but we are also talking about trying to make an incredibly hard-to-make and expensive fuel. Those two things are challenging to do together,” said Eastham, who is also part of the Brahmal Vasudevan Institute for Sustainable Aviation.
“SAF adoption is a serious, serious challenge for aviation because of the scale-up, and that's why, when you see targets for aviation, it is to try and reach 100% SAF by say 2050, and that is generally considered to be a huge lift. So, if you were to have a third runway within 15 years, you would still be 10 years from when the optimistic estimates are that we'll have 100% SAF.”
The alternative will also degrade air quality in the same way as current fuels, he added, so any increase in the number of flights taking off would still affect local and global air quality.
There is “not enough farmland on the planet” to make SAF produced from crops ethically and financially viable, said Wright, who is also director of Wright Airborne Computing. Second-generation fuels using non-food plant matter and animal waste could be a better option, he said, but third-generation fuels made using bio-engineered microbes and algae is “where it gets really interesting” because these could be both truly sustainable and scaleable.
Future pay-off
If widespread SAF use is a big challenge, electric aviation is an even bigger one. If scaled up successfully, the fuel replacement could one day power large airliners, but electric power will likely only be suited for smaller aircraft and shorter ranges.
One “optimistic” study found that electric aircraft could have a maximum range of 800km, Eastham said. “There is not much serious expectation that you will ever get medium or long-haul aircraft flying electrically, so they are limited. The best we can hope for is that they can reduce the burden that we need to fulfil using other fuels.”
Batteries’ much lower energy density compared to kerosene is a key issue. Conventionally fuelled aircraft also have the advantage of losing weight as they burn fuel, allowing them to travel further. “With batteries, it doesn't matter if they're charged or dead, you're carrying them,” Eastham said. “I don't think it makes sense energetically.”
The first electric-powered transatlantic airliner is unlikely before 2050 without an “absolute miracle – in not only technology, but physics,” Wright added.
The idea that SAF and electric planes could offset the climate impact of the third runway seems unrealistic in the short term, he said. “It pains me to say that because I don't want to downplay the usefulness of the whole concept as a long-term strategy… it's an investment in the future rather than a direct pay-off.”
Making the two options economical and scalable is a “serious challenge that the aeronautical engineering community is trying to tackle,” Eastham added. “The time scales being discussed are 25 to 50 years of continuous effort worldwide, so we have big questions to answer in terms of how we'll actually achieve that – especially if demand for aviation continues to grow.”
With the Heathrow expansion aimed at that growing demand, it is not clear if the new technologies could enable a reduction in emissions any time soon.
“Any expansion of Heathrow would need to be performed in such a manner that flexibility is available to progressively incorporate infrastructure for SAF, electric aviation technologies and hydrogen,” added Dr Albert S J van Heerden, lecturer in aerospace engineering at the University of Glasgow. “Planning for such flexibility in large, long-term infrastructure projects is usually exceedingly difficult and could add to the upfront design costs.”
A spokesperson for the government told Professional Engineering: “We are determined to get our economy moving and secure the long-term future of the UK’s aviation sector.
“All expansion proposals must demonstrate they contribute to economic growth, which is central to our Plan for Change, while remaining in line with existing environmental obligations.”
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.