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The lowdown on alternative jet fuels (amended)

Updated: Aug 11, 2020

Before the claimed "pandemic" and associated collapse of the commercial aviation industry there was a lot of social and advertisement chatter about one commercial operator being more active than the other in being environmentally friendly and consequently contributing to save our planet from destruction.

One flag carrier being particular active in its claims has been slapped on the wrist by an advertisement watchdog for being misleading in its advertisement campaigns

Here is some more insight on that subject:

As aviation professionals we know that anything you do or use in aviation has comply with international standards and there is exactly zero wiggle room unless your product or service complies with certain standards.

In powered aviation, propulsion and lift is for the most part provided by machines that use fossil fuels. The types engines are both, continuous cycle and reciprocating cycle engines. Reciprocating engines such as gasoline and diesel engines in various configurations like two stroke, four stroke, with or without induction charging etc.

Most of larger commercial aircraft are powered by non-reciprocating engines, commonly gas turbine engines, using liquid fuels, commonly known as A, A-1, JP-4, JP-8 and others. These are specifications by different standard authorities; some military, some civil.

It should be noted that in commercial aviation, propulsion engines are type certificated products. In other words, irrespective on which type airframe the engine is installed, the continuing design safety assessment and reviews are conducted by the Type Certificate Holder (TCH) of the engine who is answerable to the authorities in the state of design. For example, PT-6 safety reviews and service publications have to be approved by Transport Canada and for GE aircraft engines, the same exchange happens with FAA.

However, an aircraft type with its installed engines (type) are a complex assembly that are operated as one, so the approved fuel types with associated specs have to reflect in the aircraft type certificates. Attached are abstracts of the Type Certificate Data Sheets (TCDS) of the Airbus A320 and the Boeing 737 NG. The approved fuel types are circled.

FAA, in June 2020, released an amended Special Airworthiness Information Bulletin (NE-11-56R4), attached to the article, addressing the approved blends of fuel originating from alternative sources.

As fuel is pumped, heated, filtered, distributed and metered from the fuel tanks to the engine component and passes through many components before it's finally burned, in order for it perform according specs and in turn make the aircraft perform safely to specs, fuel properties and quality are absolutely crucial to safe operation of any aircraft.

Commercial Engine manufacturers and civil aviation regulators rely on specifications stipulated by the ASTM (American Society of Testing and Materials).

The approved standard for fuel in civil jet engines is ASTM D1655 as indicated on the two attached TCDS extracts.

ASTM developed a standard for jet fuel that contains certain blends of synthetically derived elements, for example Fisher Tropsch processed kerosene, Hydroprocessed esters and fatty acids, and a number of other processes indicated in the FAA bulletin.

Both the FAA Special Airworthiness Information bulletin as well as the ASTM D7566 spec, allows D7566 blended jet fuel to be redesigned to D1655 spec fuel which allows of a more diverse blend of jet fuel than just a petroleum based product.

I addition I found a EASA publication which contains a study dated November 2019. The disclaimer contains two contradictory statements, so in the interest of public knowledge and given the fact that the report is publicly accessible on EASA's website, I decide to post it here anyway in the context of the other public documents in this post.

It is a highly recommended read and some teasers are:

  • Aviation contributes for 3.6% to total greenhouse gas emissions (2016)

  • Sustainable (alternative) Jet fuels contribute 0.004% of total aviation Jet fuels used globally (2017)

  • The study examined how to promote increased of uptake of Sustainable Jet fuels in the future in Europe.

  • The extremely low part of sustainable Jet fuels is mainly driven by the fact that there is extremely limited production capacity of such fuels.

  • Due to the limited use if Sustainable Jet fuels, it is unclear what magnitude of CO2 emission reduction will be achieved.

  • It highlights the process of validation and approving blends of sustainable jet fuels for approved use in jet engines (ASTM D4054)

Feel free to leave questions or comment

A320 TC extract
Download PDF • 21KB
B737 TC extract
Download PDF • 54KB
Download PDF • 45KB
Download • 2.23MB

ASTM specs abbreviated
Download PDF • 54KB

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