G Norris & T Dubois, Moving the needle, Aviation Week & Space Technology, 8-21 March 2021, p 14

In US, Boeing is following the SAF path to reduce combustion emissions from aircraft, and compounds that are hydroprocessed esters and fatty acids (HEFA) are the most mature. It plans to certify all its commercial aircraft to operate on 100% SAF by 2030. Also in the frame are e-fuels. Some feedstock-to-fuel pathways have already been approved, six are under test, and a further 15 are awaiting. Rolls-Royce have tested 100% SAF satisfactorily in their Trent 1000 gas turbine engines.