Focused on the Future of Avgas: UL100 Q&A
Phillips 66® and Afton Chemical have teamed up to develop an unleaded 100 grade aviation gasoline (UL100).

For decades, Phillips 66 and Ethyl Corporation have been doing their part to provide the highest quality Grade 100LL aviation gasoline (100LL) to the piston aviation industry. Phillips 66 and Afton Chemical (Afton), sister company to Ethyl, have teamed up to develop an unleaded Grade 100 aviation gasoline (UL100) to replace 100LL to meet future industry needs. The following Q&As pertain to the research and development (R&D) and use of the Phillips 66/Afton UL100.

Q. What are the key characteristics of UL100?

A. Our vision for UL100 is that it be fully compatible with 100LL and the 100LL distribution network:

  • Service the entire fleet of general aviation aircraft
  • Meet or exceed the performance and quality characteristics of 100LL as specified in ASTM D910
  • Less hazardous engine emissions compared to 100LL
  • Minimize cost increases

Q. How does UL100 differ from 100LL?

A. The petroleum components of UL100 are the same as 100LL sold today, and a new manganese-based additive package replaces the lead package. The new additive package is comprised of manganese, a proprietary scavenger formulation, and an antioxidant. The relative percentage of petroleum components have been adjusted to optimize performance with the new additive package.

Q. What are some of the biggest challenges of replacing 100LL with UL100?

A. There are many challenges in developing a new fuel. Some of the key challenges include the needs to satisfy the engine requirements of the general aviation fleet, develop manufacturing and distribution plans, and define a pathway with the FAA to achieve approval of UL100 for the entire fleet of general aviation aircraft (i.e. fleetwide authorization).

In addition to the Phillips66/Afton UL100 R&D program, we are also heavily involved in the Piston Aviation Fuel Initiative (PAFI) Unleaded Avgas Deployment group (teams listed below) that is working to ensure a successful deployment of any new unleaded avgas.

  • State & Federal Legislative
  • Aircraft Fuels Regulations & Standards
  • Fuel Manufacturing Capability
  • Distribution System (led by Phillips 66)
  • Airport
  • Aircraft Modifications
  • Communication & Training
  • International Communications

Q. When will UL100 be available?

A. UL100 is undergoing R&D to optimize the formulation. We’re working with the FAA on a testing and approval process and targeting commercialization in 2021/2022.

Q. Will Phillips 66 manufacture UL100?

A. Work is underway to evaluate manufacturing and distribution options.

Q. What do you think of the Piston Aviation Fuel Initiative (PAFI) process?

A. The FAA PAFI process has been instrumental in working to develop a fuel evaluation and approval process where none existed. Without this process and pressure to remove lead from aviation gasoline, there would be no drive for the industry to participate in developing an unleaded replacement fuel for 100LL.

Q. What do you think of the fuels submitted to the PAFI via the FAA Screening Information Request (SIR)?

A. Phillips 66 is committed to the future of aviation gasoline, and as a member of ASTM and the PAFI Technical Evaluation Committee (TEC), we are working to define fuel specifications for any candidate’s unleaded aviation gasoline.

Q. What is your opinion of lower octane unleaded fuel as an alternative to 100LL? (e.g. premium gasoline, 94 octane unleaded aviation gasoline, etc.)

A. While low octane unleaded fuels – less than 100 motor octane number (MON) – are a satisfactory alternative for many aircraft, they are generally impractical due to the following:

  • Low octane unleaded fuels do not provide sufficient detonation protection for the portion of the fleet requiring 100LL; therefore the problem of finding a replacement fuel for these aircraft would remain unsolved.
  • Misfueling risk is increased where multiple grades of aviation gasoline are available.
  • Increased capital and maintenance costs associated with providing multiple grades of aviation gasoline at airports, e.g. additional tanks, filtration systems, dispensers, refuelers, etc.

Q. Do you expect UL100 to meet the octane demands of all aviation engines, particularly high output engines?

A. Preliminary testing of UL100 has shown equivalent octane and detonation performance compared to 100LL. Testing will continue to demonstrate performance in the most demanding engines.

Q. Do you expect that any aircraft modifications will be needed to use UL100?

A. Our goal is to avoid the need for any aircraft modifications, and we’re on target based on test results to date. We will continue to evaluate potential issues as they are identified during the R&D program and approval processes.

Q. Do you expect any change in service intervals when using UL100?

A. Our R&D program includes a comprehensive assessment of the base fuel, additive, and other factors that potentially impact service intervals. Ultimately, Phillips 66 and Afton, with guidance from FAA and engine manufacturers, will define service intervals that will provide for safe and reliable operation of your aircraft.

Q. Do you expect any change in aircraft operation when using UL100?

A. Aircraft operation is not anticipated to change, but our R&D program will address this concern.

Q. Do you expect UL100 to present concerns with health and safety?

A. Any new fuel should be evaluated using a holistic approach, focusing on the three main areas of exposure below:

Additive handling: The additives required in UL100 are produced by the additive manufacturer and shipped to the refineries. These additives, while hazardous in their pure form, present an improvement compared to the current additives used in 100LL. Further, these chemicals are handled in a controlled environment by additive handling experts and added in very small fractions to the UL100 base fuel. Typically, the additives are transferred in closed systems to minimize exposure.

Fuel handling: UL100 does not change the Safety Data Sheet (SDS) Globally Harmonized System (GHS) rating for human health nor does it change transportation vehicle and storage tank placarding required compared to 100LL. As with any gasoline, leaded or unleaded, best handling practices still apply to minimize exposure (e.g. skin contact).

Engine Emissions: The major emission from the combustion of UL100 is carbon dioxide. Smaller fractions of nitrogen oxides and hydrocarbons will also be emitted, and yet smaller fractions of ash compounds from oil and the additive will be emitted. A study is underway to characterize both gaseous and particulate emissions and use these data in a human health effects assessment.

Q. What is the active ingredient in the new manganese-based additive package?

A. Methylcyclopentadienyl Manganese Tricarbonyl (mmt®), a metallic octane boosting additive that was invented in the late 1950’s by Ethyl Corporation, is known to provide engine benefits such as octane number increase, detonation protection, valve seat recession protection, and combustion improvement.

Q. What are the health effects of manganese exposure?

A. Manganese is an essential element to the body and is regulated through normal processes. It is naturally occurring in the environment and is abundant in soil, the food we eat, water we drink, and the air we breathe. Manganese only becomes a concern in certain extreme settings where ambient air levels reach a point at which the body cannot regulate the amount of manganese in the body. For example, this risk could potentially be faced by welders working every day, for long periods in enclosed spaces, without ventilation or respiratory protection, due to the manganese emitted by the welding process.

Initial assessments confirm the expectation that the tiny amounts of manganese used in UL100 would not meaningfully increase the amounts of manganese naturally present in air. Further testing and assessment will be undertaken to confirm that any emissions from the UL100 result in the expected improved environmental performance, and all such data will be shared with the U.S. EPA and FAA for review.

For additional questions, contact Monica Silva at

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