The Unleaded Avgas Transition Aviation Rulemaking Committee that was established by the FAA 18 months ago has made its recommendations, and there are no easy answers. Despite what you have heard or read, no unleaded avgas formula is a direct replacement in every way for 100ll. The committee hopes the FAA will establish an 11-year pathway that will lead to an unleaded fuel that causes the least disruption in piston aircraft operation.
The committee’s fundamental finding is that there is no unleaded fuel–and it is highly unlikely that one can be created–that is a “drop in” replacement for leaded 100ll avgas. By “drop in” replacement the committee means a fuel that would replace 100ll with no change of any kind to aircraft operation or to the fuel supply network.
There is general agreement that lead must eventually be eliminated from avgas as it is the only remaining transportation fuel in the U.S. containing lead. The amount of lead used in all avgas in the U.S. is tiny, but it is still a target of potential litigation by environmental groups and even state and local governments.
Lead is still used in avgas to raise octane and thus allow high powered, hot running air- cooled aircraft piston engines to operate with a safe detonation margin. Even minor detonation is destructive and extremely dangerous in an aircraft engine so a replacement avgas must preserve that margin.
But there are many other unique characteristics of avgas that makes it suitable for piston aircraft including vapor pressure, storage life, cold temperature performance and compatibility with aircraft fuel system materials. Though a few existing fuel formulas may meet the minimum octane requirement, the committee found that no existing fuel can match every essential performance characteristic of 100ll.
Another huge problem the committee identified is that there are no realistic market forces to drive a transition to an unleaded fuel. Avgas volume is a microscopic segment of all transportation fuels, and sales volumes are shrinking, not growing. There are simply no financially sound reasons for fuel makers and suppliers to invest the many millions necessary to create an unleaded replacement.
There are also no FAA regulatory standards or testing methods established for avgas. Over the decades refiners developed higher performing fuels and engine makers designed engines to operate on those fuels. The FAA merely blessed the standard that was created by the industry. In other words, the improved fuels came first, and engines followed. Now we’re trying to go the other way and find a new fuel that will perform in engines designed for leaded avgas.
With the absence of market forces—read profit motive–to create a new unleaded avgas the committee believes the FAA must intervene. The committee recommends that the FAA establish a centralized facility to test candidate fuels to determine which is the optimum replacement. And then the FAA must create a streamlined certification process that will provide a method for the 200,000 plus piston powered aircraft to be approved to use a replacement fuel.
If the committee’s recommendations are adopted as many as 10 candidate fuels will be tested to determine which fuel would have the least impact on piston aircraft operation. The committee determined that testing candidate fuels will take five years once the program begins.
Once an optimum unleaded avgas replacement is indentified through extensive testing, it will be up to the market to determine how quickly the new fuel could be adopted. A key feature of any new fuel is that it be compatible with 100ll so that the piston fleet can continue to operate while fuel suppliers eventually fill the avgas network.
The committee believes a transition to unleaded fuel will take 11 years once the testing phase begins and the total cost will be around $71 million with the government investing $57.5 million and industry $13.5 million. It’s possible, even likely, that a majority of piston aircraft owners will need to make at least some modification to their aircraft to use the new fuel, even if those modifications are as minor as new certification documentation. But it’s also possible some engine/airframe combinations will need hardware changes, fuel system modifications, or even reduction in performance or weight carrying capability.
The entire process is fiendishly complicated because every aspect of piston aircraft operation will be impacted beginning with the fuel manufacturer, through the delivery and storage system, and finally to the aircraft operator. You have read and heard that direct 100ll replacements already exist and are just waiting for FAA approval. But that simply isn’t true. The transition away from leaded fuel will be many years long, expensive and we must be ready for the unexpected complications.