Sustainable Aviation Fuel is governed by ASTM International specification D7566, "Standard Specification for Aviation Turbine Fuel Containing Synthesized Hydrocarbons", which currently authorises eight numbered annexes for specific synthesis pathways. The Programme is built around three of these (two approved, one in qualification), with HTL biocrude as a fourth route that operates under D1655 co-processing rather than D7566.
SAF cannot be sold for commercial aviation use unless it complies either with ASTM D7566 (as a synthesised hydrocarbon component blended with conventional Jet A-1) or with ASTM D1655 itself (as drop-in jet fuel produced through certified pathways). Each new SAF production pathway must complete the lengthy ASTM D4054 qualification process — a multi-stage scientific, engineering, and operational testing programme typically taking five to ten years from initial submission to annex approval — before the resulting fuel can be sold and combusted in commercial aircraft.
For a national bioeconomy programme, annex status is therefore decisive: it is the difference between fuel that earns revenue and fuel that earns research grants. The Programme is structured so that two of its three SAF pathways operate within already-approved annexes from year one, and the third (MTJ-SPK) is dimensioned as contingent optionality.
| Annex | Pathway | Blend limit | Programme relevance |
|---|---|---|---|
| A1 | Fischer-Tropsch SPK (FT-SPK) — from coal, natural gas, or biomass | 50 % | Pillar II Route A. Biomass-to-FT (BTL) qualifies under this annex. |
| A2 | HEFA-SPK (Hydroprocessed Esters & Fatty Acids) — from oils and fats | 50 % | Not part of the Programme. Dominant existing global SAF pathway (~ 84 % of capacity). |
| A3 | HFS-SIP (Hydroprocessed Fermented Sugars to Synthetic Iso-Paraffins) | 10 % | Not part of the Programme. |
| A4 | FT-SPK/A (Fischer-Tropsch with aromatics) | 50 % | Adjacent to Pillar II Route A; A1 is the structurally aligned annex for paraffinic output. |
| A5 | ATJ-SPK (Alcohol-to-Jet) — from ethanol, isobutanol | 50 % | Pillar III primary route. Sugarcane ethanol qualifies. |
| A6 | CHJ (Catalytic Hydrothermolysis Jet) — from oils | 50 % | Not part of the Programme. |
| A7 | HC-HEFA-SPK from algae | 10 % | Not part of the Programme. |
| A8 | ATJ-SPK with extended feedstock list | 50 % | Adjacent to A5; same conversion chemistry; broader feedstock provisions. |
Annex list reflects ASTM D7566-24a as published. ASTM standards are continually updated; current status should be verified directly with ASTM International before commercial transactions.
The Alcohol-to-Jet Synthetic Paraffinic Kerosene pathway is the Programme's immediately bankable SAF route. It is qualified under ASTM D7566 Annex A5 for ethanol and isobutanol feedstocks, with permitted blend ratios up to 50 % by volume with conventional Jet A-1. The chemistry is well-characterised: dehydration of ethanol to ethylene; oligomerisation of ethylene to mid-chain alpha-olefins; hydrogenation to paraffins; fractionation and isomerisation.
Commercial status: LanzaJet (a 2020 spin-out from LanzaTech) commissioned the world's first dedicated commercial ATJ-SPK facility — the Freedom Pines Fuels plant in Soperton, Georgia, USA — in 2024, with capacity reported in the order of 10 million gallons per year of SAF and renewable diesel co-product. Additional LanzaJet projects are in development in the United Kingdom, the United States, India, and Japan. The Programme proposes a deliberate licensor partnership with LanzaJet or an equivalent ATJ-SPK technology provider for the first Negros Occidental ATJ unit.
The Fischer-Tropsch Synthetic Paraffinic Kerosene pathway is qualified under ASTM D7566 Annex A1 for synthesis-gas-derived feedstocks, including biomass-derived syngas (BTL, "biomass-to-liquid"). The Fischer-Tropsch synthesis process itself is industrially mature, deployed at commercial scale by Sasol (South Africa), Shell (Pearl GTL, Qatar), and others — though predominantly on coal-derived (CTL) and natural-gas-derived (GTL) syngas. The biomass-to-FT (BTL) variant uses the same Fischer-Tropsch chemistry on syngas produced by biomass gasification and is at TRL 6–7, with commercial-scale projects in advanced engineering.
For the Programme, the strategic implication is that there is no annex risk on the FT-SPK route. The certification framework already exists. The technology integration challenge is at the gasification, gas-cleaning, and FT-synthesis interface, not at the annex-approval stage. This is structurally different from a route requiring fresh ASTM qualification.
Hydrothermal liquefaction does not target a D7566 annex of its own. Instead, the HTL biocrude stream is upgraded by hydroprocessing — either at a dedicated facility or through refinery co-processing — into refinery products that meet ASTM D1655 directly. This is the same framework under which HEFA-derived diesel and jet products have historically been certified through the existing complex-refinery infrastructure.
The ASTM D1655 co-processing provisions (and the parallel international standards such as DEF STAN 91-091 in the UK) allow refineries to process biogenic feedstocks at modest co-feed ratios alongside conventional crude, producing finished jet fuel that meets the standard specification without requiring a separate D7566 annex. The Programme's HTL biocrude stream is therefore aligned with this existing framework, with no additional certification waiting period beyond the standard refinery quality-assurance protocols.
Methanol-to-Jet (MTJ-SPK) converts methanol to jet-range hydrocarbons through methanol-to-olefins (MTO) followed by olefin oligomerisation, hydrogenation, and fractionation — a chemistry adjacent to the established methanol-to-gasoline (MTG) and methanol-to-aromatics (MTA) routes. As of 2026, MTJ-SPK is not an approved annex of ASTM D7566. Multiple pathway proponents have programmes in active D4054 evaluation:
Industry and standards-body signals indicate a credible expected-approval window in the 2026–2028 timeframe, but no schedule is binding. The Programme's response to this uncertainty is structural: Pillar I's near-term economics are dimensioned to be viable on biofertilizer + CBM + methanol alone, with MTJ deployment treated as Phase-3 contingent optionality. Capital deployment for MTJ-scale conversion is sequenced after annex approval; the methanol-synthesis capacity itself is built in Phase 2 and serves marine-fuel, chemical-industry, and gasoline-blending markets in the meantime.
All current ASTM D7566 SPK annexes — A1, A4, A5, A8 — permit a maximum blend ratio of 50 % SPK with conventional Jet A-1. This 50 % blend wall arises principally because synthetic paraffinic kerosenes are essentially aromatic-free, and a small aromatic content in the final fuel is required to maintain compatibility with legacy nitrile-butadiene-rubber (NBR) seals in older aircraft fuel systems. The minimum aromatic content in finished Jet A-1 is specified at 8.0 % by volume in D1655.
Two industry trajectories address this constraint. First, the 100 % SAF (or "neat SPK") qualification framework is in active development through ASTM and through engine-OEM testing programmes; flight demonstrations on 100 % SPK have been completed on multiple platforms. Second, aromatic blend management — the deliberate addition of bio-aromatic or compatible aromatic streams to SPK to produce a finished fuel meeting the D1655 minimum aromatic content while remaining low in soot-precursor and contrail-precursor compounds — is the framework under which the DM-XTech Group's tLCAF product line operates. The Programme's SAF outputs are designed to be compatible with both trajectories.