United Will Run A Boeing 737 Engine On 100% SAF With Passengers

Today United Airlines is continuing its campaign to accelerate the uptake of Sustainable Aviation Fuels (SAFs) across the industry. The airline will run a Boeing 737 MAX engine on a blend of 100% SAF while it is flying from Chicago to Washington with more than 100 passengers onboard. This will be the first time that such a feat has been attempted.

United Airlines, SAF, Boeing 737 MAX
United Airlines will today operate a flight where 100% SAF powers one engine. Photo: United Airlines

Across the industry, airlines, airports, and manufacturers are looking at SAFs as a short-term solution to the growing issue of aviation emissions. Just yesterday, Simple Flying reported that Airbus had been operating an A350 on 100% SAF, while Embraer is looking to achieve the same feat next year.

United’s ambitious SAF project

Currently, aircraft are only generally allowed to fly on a 50/50 blend of sustainable aviation fuels and traditional fossil fuels. Like most things, exceptions can be made. These are typically made for testing. For example, the Boeing 777X can fly though it has not yet been certified.

United Airlines aims to operate such an exceptional flight today. In partnership with several parties, such as Boeing and CFM International (the aircraft’s engine maker), the airline will operate a flight from Chicago to Washington. This, in itself, isn’t a crazy feat. What makes the flight special is the fuel that it will be using. A blend of 100% SAF will power one engine of the narrowbody.

United Airlines, SAF, Boeing 737 MAX
The other engine will be powered by regular fuel to provide a direct comparison. Photo: United Airlines

Ground staff will load 500 gallons (2,273 liters) of 100% SAF into one fuel tank for one of the engines, while refuelers will place 500 gallons of conventional fossil fuel kerosene in the other tank for the other engine. The airline is attempting to show there is no operational difference between the two fuels and what better way than running them simultaneously?

Commenting on the milestone flight, Ihssane Mounir, Senior Vice President of Sales and Marketing for Boeing, said,

“As an industry, we are committed to addressing climate change, and sustainable aviation fuels are the most measurable solution to reduce aviation carbon emissions in the coming decades. No one entity can decarbonize aviation alone and it will require partnerships like this to ensure aviation is safe and sustainable for future generations.”

United Airlines, SAF, Boeing 737 MAX
Currently, only a maximum blend of 50% SAFs is approved for daily flights. Photo: United Airlines

American Airlines wants some of the attention

It seems as though American Airlines didn’t want its rival United Airlines to get all of the attention today when it comes to SAFs. Around an hour and a half after United Airlines announced its SAF flight, American Airlines made a separate announcement on the topic.

The US carrier revealed that it had signed an agreement to take delivery of 16 million gallons (72.7 million liters) of a 40/60 blend of SAF. This brings its total SAF commitments to more than 120 million gallons so far. According to the carrier, the SAFs will be delivered to San Francisco Airport over seven years.

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Strangely, this doesn’t mean that American Airlines will end up using the SAFs. At most airports, it is not possible to separate SAFs and fossil fuels for day-to-day use. This means that an airline can buy SAFs, and claim the environmental benefit from doing so, but another airline may end up burning the actual fuel.

What do you make of United Airlines’ 100% SAF on one engine flight? Let us know what you think and why in the comments!