ASTM approved SAF pathways

ASTM approved SAF pathways define the production routes that can be used to produce sustainable aviation fuel for commercial aviation under recognized fuel standards.

These pathways are approved under ASTM International ASTM D7566, the specification covering synthetic aviation turbine fuels blended with conventional jet fuel.

 

Each approved pathway must demonstrate that the resulting fuel performs safely in aircraft and remains compatible with existing aviation fuel systems.

What does ASTM approval mean for sustainable aviation fuel?

ASTM approval means a SAF pathway has demonstrated that its fuel can meet aviation fuel requirements when blended under approved specifications.

Approval confirms that the fuel:

  • meets critical fuel property requirements
  • performs reliably in turbine engines
  • remains compatible with aircraft fuel systems
  • can enter commercial aviation supply chains

 

Without ASTM approval, a fuel pathway cannot be used as commercial SAF.

What is the difference between ASTM D7566 and ASTM D1655?

ASTM D7566 governs synthetic aviation fuel blending components, while ASTM D1655 governs conventional jet fuel.

The SAF approval pathway works like this:

  1. Synthetic fuel is approved under ASTM D7566
  2. It is blended with conventional jet fuel
  3. The blended fuel is then recertified under ASTM D1655 for commercial use

 

This is why approved SAF functions as drop-in fuel within existing aviation systems.

Which SAF pathways are currently approved under ASTM D7566?

Several production routes have been approved under ASTM D7566, each using different feedstocks and chemistry.

HEFA (Hydroprocessed Esters and Fatty Acids)

HEFA converts oils and fats into synthetic paraffinic kerosene through hydrotreating and hydroprocessing.

 

Common feedstocks include:

  • used cooking oil
  • animal fats
  • vegetable oils

 

HEFA is currently one of the most commercially deployed SAF pathways. As use of sustainable aviation fuel increases, HEFA feedstock is expected to reach its limit, which will require other SAF pathways to contribute to meet projected demand.

 

Fischer-Tropsch (FT-SPK)

The Fischer-Tropsch pathway converts synthesis gas into synthetic hydrocarbons that are upgraded into aviation fuel blending components.

 

Feedstocks may include:

  • biomass
  • municipal solid waste
  • biogas
  • synthetic carbon sources

 

This pathway produces Fischer-Tropsch Synthetic Paraffinic Kerosene (FT-SPK).

 

See Fischer-Tropsch synthetic paraffinic kerosene.

 

Alcohol-to-jet (ATJ)

Alcohol-to-jet converts alcohol intermediates into aviation-range hydrocarbons through catalytic upgrading steps.

 

Typical feedstocks include:

  • ethanol
  • isobutanol

 

This pathway uses dehydration and oligomerization chemistry before hydrogenation.

 

Synthetic Iso-Paraffins (SIP)

SIP pathways convert sugars into synthetic hydrocarbon molecules suitable for aviation blending.

 

This pathway is associated with biologically derived intermediates.

 

Catalytic Hydrothermolysis (CHJ)

Catalytic hydrothermolysis converts lipid-based feedstocks into aviation fuel molecules using thermal and catalytic processing.

 

This pathway expands feedstock options within lipid-derived SAF systems.

 

Refer to ASTM.org for the latest updates. ASTM D7566-25a is current at the time of publication.

 

Why are there multiple ASTM approved pathways?

Different feedstocks require different chemistry to produce aviation-range hydrocarbons.

No single pathway fits all feedstock conditions.

 

Approved pathways allow SAF production from:

  • oils
  • waste
  • biomass
  • synthetic carbon systems

 

This creates flexibility for regional fuel development.

Why is Fischer-Tropsch important among ASTM pathways?

The Fischer-Tropsch pathway offers feedstock flexibility because many carbon sources can first be converted into synthesis gas.

This allows FT systems to support:

  • biomass-to-liquids
  • waste-to-fuels
  • Power-to-liquids pathways

 

For SAF pathway context, see Syngas to SAF.

Can ASTM-approved SAF replace conventional jet fuel completely?

Today's approved SAF pathways produce blending components rather than fully standalone jet fuel.

Blending remains necessary to ensure:

  • fuel property balance
  • material compatibility
  • aviation certification compliance

 

Research continues toward higher blend ratios and future synthetic fuels.

Frequently asked questions

Does ASTM approve feedstocks or pathways?

ASTM approves fuel production pathways and resulting fuel properties, not feedstocks alone.

Yes. FT-SPK is an approved ASTM D7566 pathway when blended according to specification.

Some synthetic fuels have lower aromatic content than conventional jet fuel and require blending to meet full fuel requirements.

Yes. ASTM pathways continue to expand as additional fuel technologies complete qualification.