George Braly

I do not disagreeing with your experience. I have not claimed that G100UL avgas if allowed to leak for extended periods of time and to evaporate at a "collection point" where it drains to - -will cause paint damage. However, it is also true that 100LL can and does do the same thing. Maybe part of what you may not appreciate is that, depending on which refinery produces the 100LL - - it can contain 34% aromatic (29% toluene) or that can be as low as 12 to 15%. If the 100LL you use is from the later refinery, then you may not see the same results as another owner using the former conforming commercially legal for sale version of 100LL. All of the aluminum integral fuel tank airframes require periodic re-works due to leaking 100LL. Are you denying that fact ?

We know exactly what the issues are with the paint. If you allow the airplane to leak fuel onto the paint continuously for hours at a time and it evaporates then it concentrates some of the components which can then begin to degrade the paint. Note - - 100LL does the same thing. Lots of examples around, including many in the Mooney community. The difference is that it takes longer with 100LL than with G100UL Avgas. Keep in mind, we have a Cirrus that has been using G100UL Avgas for 15 years. No issues. Feel free to come by Ada and inspect it or go fly in that plane with me. As to the rest of the fuel system components - - in addition to the Cirrus long term usage, see my other email about Embry Riddle Testing. In addition, in 2012-2013 the FAA supervised an extended year long fuel system component test including all of the primary fuel wetted components in both Lycoming systems and in Continental systems. Fuel pumps, gascolators, fuel selectors, check valves, dozens of old (salvage yard) components included dozens of old O rings and three different 25 year old fuel bladders. All of that passed the testing without any exceptions. If you would like to read the test reports, let me know and sometime you can come by and sit in our conference room with a box of documents and read the reports, for yourself. George

Varlajo, I think possibly you are mis-informed about the perceived absence of fully independent testing. Consider the completely independent testing done for a year by Embry Riddle. That testing included extensive material compatibility testing; Extensive real world flight testing conducted by ERAU pilots; Engine durability testing with engine tear down and parts inspection / measurement; And extensive on-aircraft "F & R" testing. (Functionality and Reliability testing.) Consider the two years of extensive material compatibility testing conducted by Cirrus Aircraft. They wrote the report stating that all of that testing was completely successful. Using their test equipment and their engineers and their test plans. We were not involved in any way other than to supply them a batch of "worst case" (for material compatibility testing). In addition, Cirrus conducted flight testing using the same airframe and test plans that they had used for conducting PAFI flight testing on multiple fuels which all failed. ******** There is a lot of willful or otherwise "uninformed" mis-information floating around. Your complaint about desiring independent testing is completely understandable. Which is why the FAA agreed to going to the trouble to oversee that testing. If you have more questions, please feel free to ask. Regards, George

Chris, A lot of people not involved in actual FAA aircraft and engine certification work may not appreciate the "science" of when "good enough" is "good enough". Lycoming and Continental can certify a brand new - - "clean sheet" engine design and get it certified by doing a single 150 hour engine test - - following a defined / prescribed "protocol". Then they can produce them and sell them as fast as they can make them, if they have customers. One engine. 150 hours. In engineering, we should normally be looking for "boundary conditions". If you, "worst case" conditions or applications. For example, GAMI, unlike the PAFI program, was able to work with the FAA to identify a "worst case" (i.e., boundary condition) engine and associated operating conditions, so that a then "robust" detonation test matrix, executed on that "worst case" (boundary condition) engine would establish that all of the remaining engines, operating under design and operating envelope conditions which are then known to be "less severe" than the "test day" engine & operating conditions - - would be assured of being able to operate on G100UL Avgas free of detonation. Otherwise, if you approach the problem in any other manner, you end up with a constant chorus of "... Yeah! But - - but - - but whattabout my IO-550 with 9:1 CR" or . . . "... whatabbout our R-2800 on our CAF A26 or our CW-3350 on FIFI ?" The same applies to "hot day / hot fuel" climb cooling / vapor lock testing. On September 5th, 2012, we completed that testing under direct supervision / participation of four senior FAA propulsion engineers who were on site at GAMI. By requirement - - it was a real 100+F OAT day. (105F to be exact). At Ada, that translates into a 110 degree day at S.L. With fuel that was custom produced to be very near the maximum permissible Reid Vapor Pressure. AND to do that "back to back" same-day - - using 100LL that was also custom blended to be near the upper end of the RVP range permitted in the specification. AND, to do that on a turbocharged engine at various altitudes up to and including 25,000 feet. With fuel temperature sensors scattered around to record the temperature of the two fuels in the fuel tanks and at the firewall and coming out of the gascolator going into the fuel pump. It is that type of approach, using a "boundary condition" philosophy for the testing that allows any progress to be made in the general aviation aircraft world. Yes, some things are statistical - - fatigue cracks are an example. When we did the repair on the wing structure of the fleet of T-34s - - that was a requirement for portions. Example, we developed a new high strength wing bolt using a well proven state of the art metallurgy. Lots of fatigue/damage tolerant engineers would look at the specification for that material and simply "nod their heads" that was good enough. However, we took multiple samples of the new bolts and the old bolts to the test lab. All of the old bolts broke between 75 and 79,000 lbs of tensile load. All of the new bolt design broke between 94 and 97,000 lbs. That is an example of the application of testing multiple articles - - when it is appropriate. So, in our judgment, and that of the FAA, the approach we used for the certification of G100UL was appropriate. I think one of our failings was in our lack of robust understanding or appreciation of the issues involved with our rapidly aging fleet of aircraft. (Example, the Mooney fatal crash in Australia, two years ago, due to a 29 year old nitrile O-ring that failed in 100LL and caused a fuel leak in the engine compartment. - - - if that aircraft had been using G100UL avgas then the fuel would have been blamed for that tragedy.) One other thought: There is no perfect fuel. Not 100LL. Not G100UL avgas. Your questions and concerns are always welcome. George

Like all good studies, the larger the pool of data, the better. 150 aircraft is, in my opinion, not a very good representation of GA as a whole. Like others have said, a 3% failure rate is completely unacceptable. Even in the industry I work in. A 3% failure rate in aircraft? I think should potentially be fleet grounding. The only issues for which the FAA will "ground" an aircraft is for some type of demonstrative "Safety of Flight" issue. None of the reported in-service difficulties have involved any type of "safety of flight" issue. The FAA has maintained a spreadsheet on each of these and agrees that there is no safety of flight issue. As for the occasional "splashed" droplet on the paint - - there are a couple of routine and easy ways to deal with that. Any kind of routine "shop rag" in hour hip pocket or even a paper towel in your baggage compartment will clean that up and now result in any visible change to the paint. In addition, we have handed out refueling mats with the STCs, beginning at RHV. These are grey absorbent mats with a 3" hole in the middle. You can keep a half-dozen of them in the baggage compartment. They can be reused multiple times. If you use those, then they also protect the paint surface from being scratched or damaged by the refueler allowing the refueling nozzle to to rest on the surface of the wing (which we have observed from time to time.) As also mentioned, some of the crystal / graphene coatings are very effective at protecting the paint. With respect to sump drains, there really should not be any splashing or droplet from those, but again, it takes no more than about 10 seconds to wipe the area around the filler port with a red shop rag when you finish with the sump drain. In our experience - - so far, - - if your tanks are not leaking 100LL, then using G100UL avgas does not cause them to initiate leakage. George

There are several Mooneys that have used G100UL Avgas. No leaks and no paint damage. I borescoped the fuel tank of one Mooney that had leaked. There were at least two (likely three) different types of internal sealant applications (wrong sealant - wrong technique) clearly visible where someone had tried to do field repairs of earlier 100LL leakage. There are three shops around the country that specialize in stripping the interior fuel tank sealant and then applying new sealant - - - properly applying new sealant. (Note the factory applied sealant was never properly applied by the factory - - according to the repair shops.) Basically, those repair shops tell us that any Mooney with more than about 20 years since factory sealant is a ticking leak-bomb for fuel leakage. I inspected a Mooney at RHV that had been using G100UL Avgas for several months. No evidence of any issues. I asked the owner if I could borescope his fuel tanks. He grinned and approved. When I looked in the tank the sealant was as pristine and perfect as you could ever expect. When I quizzed the owner, he grinned and told me that his plane started leaking 100LL when it was about 15 years old. He had it resealed about 8 years previous - - at "Weep No More" (shop in Minnesota that specializes in resealing fuel tanks.) *********** There are about 150 aircraft that have used G100UL Avgas. Of that number, there are 5 that have reported in-service issues that did not have clear evidence of prior leakage of 100LL. If you spill G100UL on your wing during refueling - - and clean it up ("Good fuel hygiene") before it evaporates and dries out in sunlight) then it does no damage to the paint. If you spill it and let it sit and evaporate for a while, without cleaning it up, then it will slightly stain the paint a brownish color. Various ones of the popular crystal coatings offer substantial protection of the paint. A couple of those commercial products are extremely effective at protecting the paint from stains and damage and have a number of other general benefits with respect to improving the durability of the paint and greatly enhancing the ability to clean bugs and debris from the wings. George

Mike, I am aware where those photos came from. I have been double checking and trying to verify from some contacts in PAFI / EAGLE that those pictures are from 100LL. As a side matter - - PAFI / EAGLE has been less than "transparent" about a lot of their data. Also, there are not and have not been any fuels in the PAFI program with significant aromatics that have been tested by PAFI / EAGLE. However, based on my understanding of the various aircraft that were tested and that used those various test fuels I have reason to believe this airplane make/model was not one of the PAFI test planes. I think the PAFI / EAGLE folks may have used this as a convenient example. In any event, there are other similar pictures available that demonstrate similar appearances that were documented from years ago before PAFI/EAGLE ever came into existence. When I run across those, I will try to post those up, also.

Marc, I wish I had the band-width to jump into this with more time and data. However, claims that 100LL does not damage paint - - are contrary to lots of observations from the field. Let me try to verify the source of the fuel in that photograph - - in the mean time, I deleted it from the post. I apologize for any confusion. Let me try to get better data. In the mean time, I have to (get to) go fly a new experimental turbo system! George

Schllc, Give me a call tonight or tomorrow sometime. I would like to discuss this with you. 580 421 5645 is my cell number. Do you have borescope pictures of the inside of your Mooney fuel tanks ? George PS. As an interesting coincidence: - - My name is on some of the original 1967 engineering drawings when (in the engineering room at Northridge, Ca.) we redesigned the Aerostar wing tanks (which had, for the Aerostar "360 & 400", previously been "dry wings" - - to become "wet wings." That was for the prototype and then the production series of Aerostar 600,601, & 601P models.

With respect to your observation: "If it does NOT leak with 100LL . . . " Mike, Integral (non-bladder non-welded) aluminum - riveted fuel tanks have been leaking (on 100LL ) within relatively short periods of time (2 to 10 years after original construction) since at least the 1970s. There are three long term repair shops that specialize in cleaning and re-sealing Mooney integral fuel tanks (and others of similar construction.) Examples: 1) Mooney fuel leak 100LL https://youtube.com/shorts/rMqENgH2udo?si=5_aVNdzOYtqxfmmI 2) Identifying a leak on a Vans RV-10 fuel tank - 100LL https://youtube.com/shorts/-zXeFLsfUhU?si=F09FtUxW26eAUmIS 3) Cirrus SR20 fuel leak from 100LL https://youtube.com/shorts/3j53EHFpVzo?si=0RZa31jYdr8QhUg6 4) Resealing a leaking Piper fuel tank. https://youtube.com/shorts/K4FwEgt86iQ?si=21tI-6xqaaDxKHD8

I agree - - That looks like they did a nice job. I think all three of the companies that do (re-do) Mooney fuel tanks do a much better job than was originally done at the factory. But there are several devils in the details that are not detectable from visual inspection. Examples: A) Proper cleaning of the old sealant is extremely important; B ) and then there is fairly detailed requirements for "surface preparation". C) Then there is normally a "recommended" "adhesion promoter" - - which very few shops use. It is not mandatory. But it sure does help in improving adhesion to the substrate. D) Each sealant variety has a different "pot" or "useful working life" after the two parts are first mixed together. If it is 30 minutes, and you are still putting sealant down at 35 minutes, then the cross-linking of the molecules in the sealant with the substrate will be greatly degraded. Those are among the several things we have learned as we investigated material compatibility issues with sealants over the last several years.

Nicely done. Very. Do you know when your tanks were last sealed ? If ever ? Or how old the sealant was before you had the tanks resealed ? George BTW - - one is at a loss for words to describe the difference in the quality of the workmanship - - "before" and "after". Unfortunately - - the condition of your tanks before being resealed is something we have seen before.

https://youtu.be/Q4MgLkTamP4 Documentation for the G100UL Avgas drip-evaporate-drip-evaporate paint testing. On a lighter note: What you see is definitely a breach of the protocol for practicing good fuel hygiene!

You are misinformed. There is standard liability coverage for the fuel being sold to the FBOs in California and elsewhere. Identical or essentially identical to that presently in place for most of the FBOs selling 100LL.

I have been ramp checked (randomly) at least six or 8 times over the years. More recently - - when we were at the AOPA airshow in Buckeye Arizona last year - - two FAA inspectors showed up on the ramp in a golf cart while we were installing the STC and placards on the Baron owned by California Aeronautical University which they brought down to do formation fly overs at the Buckeye air show in two Barons operating on G100UL Avgas. Initially, the two FAA inspector's "attitude" was in full blown "enforcement" mode. They were a bit in disbelief that we were actually going to put unleaded avgas in the CAU baron. So they demanded to see all of the paperwork. STC. Installation Instructions; ICAs; Apprvd FMS; etc. While they were standing there we were putting the placards on the wings next to the fuel filler ports. About that time, a local I.A. drove up in a golf cart and jumped out and said, "where do I sign ?" He signed off the log book and the 337 and left. The two FAA inspectors walked around the airplane and came back to me and thanked me for our cooperation and expressed their satisfaction that all of the paperwork details were in good order.

I think, sometime in the 1990s, the Congress made it a federal criminal offense to use an STC without the required permission of the owner of the STC. But I have not gone back and verified that in 15 years or so. My memory may be fooling me. That happened because of complaints that people were just doing xerox copies of their neighbor's STCs.

The missing pieces of paint (very old paint) were already present when the airplane came to GAMI in Ada in October of 2023. The tan / brown staining on the fuel cap is from fuel spills after the airplane left GAMI sometime in the spring of 2024. It had been refueled by us multiple times with no brown stains. The "good fuel hygiene" protocol is to simply absorb / wipe up the fuel in a timely manner, if it is spilled. How to prevent ? A good application of crystal coating or a graphene coating in that area is very helpful. Good fuel hygiene is still called for. But with the crystal or graphene coatings, one can often "buff out" any stain - - but it takes some elbow grease. In fact, after our extensive testing of those coatings during the summer and fall of 2024, I am seriously impressed by their effectiveness. Simple to apply. Makes maintaining the paint (anywhere) on the aircraft much easier, and makes bug removal on the leading edges much easier.

In the case of the four airplanes we have run tests on, the OEM elastomeric components were traditional nitrile.

I thought I had made that clear. If not, my apologies. They were the OEM designated O-rings and seals. They were not replaced or "upgraded" before any of the testing.

Actually - - a Lycoming IO-360 is one of those engines.

Respectfully, I think the request to identify any candidate fuel that even, now, remotely, claims to be suitable for use for the fleet - - without significant individual modifications to the engines - - is rather important to your questions. Someone can be "... working on a fuel" - - but if that fuel is not going to meet the goal as being useful for the entire fleet of airplanes and engines - - then the significance of each of those efforts is rather seriously diminished. " Do you think another company is not capable of producing a product to compete with GAMI? " What I think is likely irrelevant. What I know is that the P66, Shell, and others have claimed to be working towards that goal for the last 30 years. Both P66 and Shell failed - - miserably - - during their participation in the PAFI program and formally withdrew any further participation in that program.

Please identify each sponsor of an Unleaded High Octane candidate replacement for 100LL who has not publicly stated or acknowledged that their candidate UL fuel will require modifications of the engines in order to pass detonation test requirements.

Please share with me any information you may have on that subject of Shell in Europe doing testing on a new fuel formulation. There is no hint of that within the EAGLE / PAFI group to the best of my knowledge . Further, just before Christmas, I was in Europe and I meet with several of the senior leaders in the European general aviation world and they had no knowledge of any activity for a high octane unleaded fuel being developed anywhere within the European Union or in the United Kingdom.

As I understand the situation - - Shell currently does not produce one drop of 100LL anywhere in the United States. I think it still produces some 100LL - - maybe in Holland. Again - - there are a lot of "facts" associated with this 30 year process. It takes a "deep dive" into both the current and past refining structure / infrastructure and a similar deep dive into the (so far) unproductive "industry" (ASTM / FAA / Taxpayer / PAFI / EAGLE) history to fully appreciate how we got to where we are today.

The Swift 100R has about 25% ETBE. But the ethanol fraction of the ETBE is supposed to be controlled by an ASTM production spec for ETBE so that it is not more than 1% of the ETBE. So the amount of ethanol in Swift 100R should be relatively small. [However, we have seen some very peculiar material compatibility issues with 25% ETBE fuel chemistries.] The basic Swift Patents suggest a fuel chemistry that would be ~ 25% ETBE & 70% "high grade aviation alkylate" and ~ 3-5% butanes or iso-butanes for vapor pressure. Swift claims the "supercharge" rating is > than 130. But that is only obtained at a F/A ratio that is "off scale" higher than any actual F/A ratio that is used by our engines. The ASTM D909 laboratory supercharge test data for one similar fuel chemistry reflects a supercharge rating of only around 115 (rather than ~ 130 for 100LL and > 150 for G100UL avgas) at the full power / full rich Fuel-Air ratios typical of our fleet of high powered engines. ETBE is potentially useful for aviation gasoline, but only if one is able to "manage" or "mitigate" ETBE's own set of problems. The detonation characteristics are such that it is - - (in our judgment, and based on our test data of ETBE fuel blends we have made IAW the reported Swift 100R fuel chemistry and then tested in back to back testing with 100LL and G100UL avgas on our test stand) - - rather unlikely that Swift 100R could be used for any of the high powered engines without significant "adjustments" to the engines, such as retarding the timing or reducing the redline CHTS and imposing limits on the IAT, or likely, some combination of all of the above. But we may be "missing something" in our evaluation and analysis. Always open to new information.