What’s the difference between synthesized and sustainable aviation fuels?

Effectivity: All aircraft 

ATA: 28  

By: Marc Cadotte – Technical Services 

Here at Bombardier, operators often ask us this question: 

In the SAF acronym related to aviation fuel, does the ‘S’ stand for ¨sustainable¨ or ¨synthesized¨ aviation fuel? 

To clear up the confusion, we will first provide a bit of historical explanation.  

In the recent past, approval data was introduced in all Bombardier aircraft flight manuals (AFMs) in the Limitations Section 02-05-01. It introduced the aviation turbine fuel containing synthesized hydrocarbon as specified below:  

 ASTM D1655 is the standard specification for aviation fuel. 

ASTM D7566 is related to the specification for aviation turbine fuel containing synthesized hydrocarbons. 

So, one may say that the answer is quite simple: the ‘S’ in SAF officially means synthesized. But what about the SAF acronym accepted by most aircraft operators as being sustainable aviation fuel, and where does it fit in the above AFM modification?

Presently, the certified pure unblended aviation fuel produced from a sustainable source must first meet a requirement that is part of an annex of ASTM Specification D7566. 

Therefore, sustainable aviation fuel is only one of the different types of synthetized fuel presently produced and certified under ASTM D7566. Various source of sustainable product and various batches of sustainable aviation fuel produced need to demonstrate compliance with the requirements of ASTM D7566 to be approved. It is then introduced as a blend with conventional jet fossil fuel, according to the blending requirements also found in ASTM D7566. The blend made from fossil and synthesized fuels is then re-tested to show compliance.  

Once the blend has demonstrated compliance with the relevant aviation turbine fuel specifications (ASTM D7566), it may be considered and certified as conventional jet fuel under ASTM D1655 and identified as such. 

In conclusion, there could be different types of ASTM D7566 synthetized fuel. The sustainable source is just one of them. 

Currently, all Bombardier business aircraft accept the different sources of fuel certified under ASTM D7566.