Sustainability: An Insight Into Airbus’ 100% SAF Flights

Airbus has been testing Sustainable Aviation Fuel (SAF) on its test flights for quite some time. SAF is a fuel blended with up to 50% conventional jet fuel, requiring no aircraft or engine modifications. Various SAFs use waste-based sustainable feedstocks, including biomass, used fat or oil, municipal waste, and agricultural waste and residues.

Using SAF can reduce the lifecycle carbon emissions by up to 80% compared to conventional fuel. Airbus’ customers (airlines and other operators) have also independently tested SAF during commercial operations.

However, all Airbus commercial aircraft, military aircraft, and helicopters can fly with up to a 50% blend of SAF. During test flights, SAF is typically used on one of the two engines, and the flight performance (with reduced emissions) is measured. Airbus aims to ensure 100% SAF capability (on all operational engines) by 2030 for most of its products.

The first 100% SAF flight

In November 2021, Airbus flew its first flight with 100% SAF (unblended) on both engines of the Airbus A350 aircraft. Two Rolls-Royce Trent XWB engines powered the test aircraft. The 100% SAF flight aims to ensure that the aviation industry (particularly the commercial sector) is ready for the large-scale use of SAF. Moreover, the SAF flights at Airbus are part of the larger initiative to decarbonize the aviation industry.

Photo: Tom Boon | Simple Flying

Airbus aims to perform ground and in-flight emissions tests to gather sufficient data to accurately determine the advantages of SAF over conventional jet fuel. Carbon emission data from ground tests gets compared to the particulate data obtained behind the aircraft during flight. A German Aerospace Center (DLR) Falcon aircraft flew in close proximity to the A350 test aircraft, taking measurements of the emitted particulate matter. According to Steven Le Moing, the New Energy Program Manager at Airbus,

Engines and fuel systems can be tested on the ground but the only way to gather the full set of emissions data necessary for this program to be successful is to fly an aircraft in real conditions. In-flight testing of the A350 offers the advantage of characterizing direct and indirect engine emissions, including particulates from behind an aircraft at high altitude.

The SAF flight research from Airbus complements research conducted by Rolls-Royce, which tests its Trent XWB engines. The Director of Product Development and Technology at Rolls-Royce, Simon Burr, states,

This research adds to tests we’ve already carried out on our engines, both on the ground and in the air, which have found no engineering obstacle to our engines running on 100% SAF. If we are to truly decarbonize long-haul air travel, then 100% SAF is a critical element, and we are committed to supporting its certification for service.

The measurements compared in-flight emissions of both kerosene and SAF (Neste’s hydro-processed esters and fatty acid, HEFA, sustainable fuel). Initial findings from the flight tests showed that the SAF has a significantly lower carbon footprint over its life cycle than conventional jet fuel. Moreover, the SAF is very advantageous in reducing non-CO2 effects too. Compliance tests using 100% SAF showed operational reliability of the SAF with no issues during flight.

The Military test flight

In November 2022, Airbus and its industry partners carried out another 100% SAF (on both engines) flight, this time on a military variant of an Airbus A330 (A330MRTT). Airbus aimed to pave the way for sustainable air transport for military operations. The Airbus A330MRTT, a Royal Air Force (RAF) voyager, took to the skies above RAF Brize Norton in Oxfordshire, England.

Photo: Ministry of Defense

Airbus conducted the test flight in partnership with the RAF, UK Ministry of Defence, the British aircraft leasing company Airlanker, and Rolls-Royce. Such flights aim to lessen the RAF’s reliance on global fuel supply chains while improving operational resilience. According to the Chief of the Air Staff, Air Chief Marshal Sir Mike Wigston,

Climate change is a transnational challenge that threatens our resilience, our security and our collective prosperity. That is why I have set the RAF the ambitious challenge of becoming the world’s first net-zero Air Force by 2040.

The 90-minute return flight replicated an air-to-air refueling sortie, demonstrating potential capabilities viable for the United Kingdom’s defense sector. Data from the in-inflight tests correlated with ground tests, which showed that SAF was operationally comparable to jet fuel. According to the Captain of the flight, Jesus Ruiz,

From the crew perspective, the SAF operation was transparent, meaning that no differences were observed operationally. The Test Plan was exhaustive and robust and has allowed us to compare SAF with JET1 culminating in a flight without a single drop of fossil fuel.

The narrowbody test flight

In March, Airbus’ most popular aircraft, The A321neo takes to the skies with 100% SAF aviation fuel on both of the CFM International LEAP-1A engines. The recent flight is part of Airbus’ VOLCAN (VOL ave Carburants, Alternatifs, Nouveaux) project. It is a joint project between Airbus, Safran, Dassault Aviation, ONERA, and the French Ministry of Transport. According to Tim Leigh, the VOLCAN Project Lead,

“At Airbus, we understand we need to go beyond CO2 emissions to gain a more complete picture of aviation’s full climate impact.”

Co-funded by the French Council for Civil Aeronautical Research (CORAC), the project aims to analyze the compatibility of unblended SAF with single-aisle aircraft. With the compatibility of SAF with commercial aircraft engines and fuel systems a primary goal, the Airbus A320 family conveniently becomes the ideal candidate for single-aisle aircraft tests. According to Airbus,

Sustainable Aviation Fuel (SAF) is a key element for the future reduction of air transportation’s carbon footprint, and Airbus is continuing its testing of this bio-jet fuel with a new VOLCAN flight test campaign using the best-selling A320 Family aircraft.

The critical emission data must be obtained at a certain distance away from the aircraft during flight. A highly modified Dassault aircraft from DLR few within 330 ft (100 meters) of the A321neo SAF test aircraft. The testbed sensors captured the emissions data for detailed analysis. While Airbus has not yet released findings from the recent flight test, it aims to expand its SAF research in the narrowbody aircraft market.

What are your thoughts on Airbus’ test flight with 100% SAF on both engines? When do you see such flight becoming the norm in commercial aviation? Tell us in the comments section.