Making sure SAF is fit to fly
SAF must have the same chemical qualities and characteristics as conventional jet fuel. This is important to ensure that manufacturers do not have to redesign engines or aircraft, and that fuel suppliers and airports do not have to build new fuel delivery systems. To ensure technical and safety compliance, SAF must undergo strict laboratory, ground and flight tests under an internationally-recognised standard. Once the SAF has demonstrated compliance with the requirements, it is blended with conventional jet fuel and re-tested.
Why does a blend limit exist?
At present, SAF must be blended with conventional jet fuel (up to 50%). Some less environmentally favourable components of conventional jet fuel (e.g. sulphur) allow seals to swell in engines and prevent fuel leaks. Newer engines do not have this concern, and SAF has been performance tested at 100% in military aircraft. It is likely that higher blend limits will be approved in the future as synthetic aromatic compounds are approved for use and as major aircraft manufacturers work to ensure aircraft are compatible with 100% SAF by around 2030.
Testing
Safety is the aviation industry’s top priority, therefore the process for testing potential new fuels is extremely rigorous. Through testing in laboratories, in equipment on the ground, and under the extreme conditions of in-flight operations, an exhaustive process determines the suitability of SAF.
Today's SAF has similar properties to conventional jet fuel, Jet A-1. Tests look at specific fuel consumption at several power settings, from ground idle to take-off speed, which is then compared to performance with conventional jet fuel. The amount of time it takes for the engine to start, how well the fuel stays ignited in the engine, and how the fuel performs in acceleration and deceleration, are all tested thoroughly. Tests are also completed to ensure fuels don’t have a negative impact on the materials used in building aircraft and components.
Once the lab and ground tests have been completed, the fuel is tested on aircraft under normal operating conditions. During the test flight, pilots perform a number of standard tests, as well as simulating exceptional circumstances, to ensure the fuel can withstand use under any operating conditions.
The aerospace sector is currently working and testing 100% SAF, to ensure aircraft can be operated on it without the current blend limits.
