Based on the G100UL fuel leak thread what's your position?

[Z W]

2 hours ago, tony said:

A recommended practice to deviate from the type design with no paper work to back up the change?

I am not an A&P nor an IA, but I believe most of us are flying around in airplanes that may no longer conform exactly to the type design and that are full of parts not shown in the parts catalog. Examples include starter and main power solenoids, voltage regulators, SCAT/SCEET tubing, fine wire spark plugs, engine baffle seals, door and window seals, main ship batteries, and many other parts where the OEM part is no longer available but FAA-PMA replacement parts exist.

My understanding of this is that an A&P or IA could swap out a nitrile O-ring with an identical one made of Viton if they are confident it will not impact the service of the part or the airworthiness of the aircraft. Am I wrong?

[A64Pilot]

4 hours ago, Z W said:

I learned some things about O-rings from all this. I guess I shouldn't be surprised the world continues to use and sell inferior-grade materials that are a few pennies cheaper.

Viton O-rings appear to be easily available for purchase for not a lot of money.

It’s getting parts that are aviation approved that may be the issue, and that’s a tough call. For instance I know of no butt splices that are specifically approved, but the wire required has very specific qualifications. Thankfully the wire is readily available though so not an issue.

Just as an example, Stat -O- Seals it seems are getting very difficult to find, but I can order them that aren’t approved aircraft parts readily and I can’t tell the difference. So what do you do? Reuse an obviously deteriorating seal because you can’t get the correct one, or replace it with a non approved one?

Thats where in my opinion the FAA SB on aging aircraft parts helps, but then your using an Advisory pub to justify not following a Regulation, and that’s flakey, putting the responsibility and liability off of the FAA and onto the mechanic.

FAA seems to be very concerned about liability or responsibility anyway, I guess admin types are concerned about their careers first and foremost? 

[EricJ]

50 minutes ago, Z W said:

I am not an A&P nor an IA, but I believe most of us are flying around in airplanes that may no longer conform exactly to the type design and that are full of parts not shown in the parts catalog. Examples include starter and main power solenoids, voltage regulators, SCAT/SCEET tubing, fine wire spark plugs, engine baffle seals, door and window seals, main ship batteries, and many other parts where the OEM part is no longer available but FAA-PMA replacement parts exist.

My understanding of this is that an A&P or IA could swap out a nitrile O-ring with an identical one made of Viton if they are confident it will not impact the service of the part or the airworthiness of the aircraft. Am I wrong?

Materials substitution is very tricky.   How does an A&P or IA know what the long-term effects of a material substitution is going to be?   Mechanics aren't chemists or engineers (usually).   The actual job of an A&P is to do maintenance and repairs using approved methods.   As mentioned previously, IPCs and parts manuals exist so that the correct part gets replaced in the aircraft, and fuel systems are important enough that I'd totally understand any mechanic's reluctance to deviate from the IPC.

Many of us use ACs and legal opinion letters and other relevant guidance to make adjustments and substitutions where appropriate, but many mechanics just stick with the IPC as much as they can because that is the conservative approach from a regulatory and even potential safety perspective.   For this reason it seems strange to me that a fuel vendor would not be diligent to inform users or potential users that their fuel may have undesirable effects on stock, OEM, manufacturer-indicated parts installed in an aircraft.  Saying that parts should have been changed out by now or may be changed at the next opportunity seems to indicate to me either a gross failure to understand how GA maintenance is done or some disingenuousness or just a CYA move.

 

[Sabremech]

44 minutes ago, Z W said:

I am not an A&P nor an IA, but I believe most of us are flying around in airplanes that may no longer conform exactly to the type design and that are full of parts not shown in the parts catalog. Examples include starter and main power solenoids, voltage regulators, SCAT/SCEET tubing, fine wire spark plugs, engine baffle seals, door and window seals, main ship batteries, and many other parts where the OEM part is no longer available but FAA-PMA replacement parts exist.

My understanding of this is that an A&P or IA could swap out a nitrile O-ring with an identical one made of Viton if they are confident it will not impact the service of the part or the airworthiness of the aircraft. Am I wrong?

I am an A&P with an IA and I’m not going to go outside what is listed in the manufacturers IPC unless the part is obsolete and not obtainable. Then I’ll work another way to find a part that will work in form, fit and function. There’s millions of o-rings of all sizes including metric. Why do I want to take on the liability of researching to find an alternate O-ring and not be sure it’s correct? What owner wants to pay for my time to research this and hope it’s right? This is a no win for mechanics. 

[MikeOH]

23 minutes ago, EricJ said:

Saying that parts should have been changed out by now or may be changed at the next opportunity seems to indicate to me either a gross failure to understand how GA maintenance is done or some disingenuousness or just a CYA move.

EXACTLY!

Blaming 'old' parts/paint or the aircraft design (e.g. o-ring material), which have worked fine for decades, to compensate for poor fuel design is a bit disingenuous, at best.

If G100UL had been developed by Big Oil, would we be so 'accommodating' with these revelations?

[A64Pilot]

Ref paint and “plastics” material compatibility with solvents, the two pics I attached are my Chinese made parts washer, that I feel pretty sure was likely meant only for water based cleaning fluid, but it’s lasted for at least two years before it failed, so effects if any may take a long time to surface, and if you test only new products they may be fine, but older ones exposed to other solvents may not, then add in every other possibility like 100+ degrees desert temps and deep sub zero temps, you’ll maybe concede that the only way to truly know is to field it and closely monitor it, or cross your fingers and hope for the best.

 

[MikeOH]

13 minutes ago, A64Pilot said:

... or cross your fingers and hope for the best.

THIS is what G100UL is starting to feel like...

[Z W]

2 hours ago, Sabremech said:

What owner wants to pay for my time to research this and hope it’s right? This is a no win for mechanics. 

If a nitrile O-ring is available from Aircraft Spruce with a MS part number and costs $0.25, but a Viton O-ring is also available, either from Aircraft Spruce or elsewhere, for $1.50, and is identical in size and function but will not swell if exposed to high-aromatic 100LL or G100UL gas and lasts 10x as long, and will not deform if exposed to high pressure, I would happily pay you or another A&P/IA to research that and install the superior product. Maybe just me, but there's one data point.

[EricJ]

6 minutes ago, Z W said:

If a nitrile O-ring is available from Aircraft Spruce with a MS part number and costs $0.25, but a Viton O-ring is also available, either from Aircraft Spruce or elsewhere, for $1.50, and is identical in size and function but will not swell if exposed to high-aromatic 100LL or G100UL gas and lasts 10x as long, and will not deform if exposed to high pressure, I would happily pay you or another A&P/IA to research that and install the superior product. Maybe just me, but there's one data point.

And that's fine, and commendable, but that's not most of GA.   

[Greg Ellis]

The talk about O-rings brings up another issue at least for my C model.  My fuel caps are the thermos style caps.  They use either the Buna (I think that is what it is called) or nitrile rubber which is already difficult to find.  I have never seen them in Viton.  Could be a major issue if the G100UL doesn’t play well with the nitrile rubber.

[T. Peterson]

On 12/22/2024 at 10:42 PM, PT20J said:

Don't you mean until the pry the 100LL nozzle from my cold, dead CB hands?

That works too!

[Marc_B]

It would be helpful if we knew:

1) what materials were tested by GAMI and how; what was test protocol and what was fuel/aromatic spec for testing

2) what materials were shown to have swelling, deterioration or deformity with testing; which sealants have been tested and how; are there certain airframes or sealing processes that are more susceptible to G100UL

3) what is the fuel/hydrocarbon spec for the California G100UL

4) have any tests been run on fuel with aircraft damage to test for contamination of fuel

5) how does GAMI explain the cases seen with obvious paint damage that appears to be escalated by use of G100UL

6) are changes planned for the Instructions for Continued Airworthiness 

7) has testing been done with ceramic coating, wax, varying ages of paint, etc to say what might be protective/preventative of staining/damage and to what degree

 

It seems that Mr Braly is somewhat open to engaging with answers and explanations. Let’s hope it stays that way vs the idea that if you don’t like it then don’t buy it…until you HAVE to because there’s no longer an option.

 

Also keep in mind that we don’t know what the exact composition of G100UL is, and there may be some variation in fuel tested in the lab years ago and fuel sold at the pump recently. The SDS shows 20-40% xylene and that’s a pretty big variation. Were the extremes of the conforming “recipe” tested or perhaps maybe a less “aggressive” mix?

It will be interesting to see what the “best” future mix is for octane…oxygenates, aromatics, metallics, or a combination?? Certainly use of lead allowed lower amounts of aromatics to meet 100/130 spec and I believe Mr. Braly has said that G100UL supercharge octane rating is much higher, 145+?  That’s from aromatics that are known to cause issues with elastomers.

But if I’m going to either choose to use, or have to use, I want to do this in the safest most appropriate way. Instructions to change these specific o-rings for my particular airframe and reseal a tank prior to safe use is one thing. Finding out after the fact with damage is completely another. 

[T. Peterson]

Much discussion of the effects of G100 on components. What about our bodies? Wasn’t the whole driver of replacing 100LL a search for something that would not kill the little chilren?? So the new stuff melts paint, swells rubber and not a word about the lil chilren?? I don’t want to touch the stuff, much less put it in my airplane!

[Sabremech]

2 hours ago, Z W said:

If a nitrile O-ring is available from Aircraft Spruce with a MS part number and costs $0.25, but a Viton O-ring is also available, either from Aircraft Spruce or elsewhere, for $1.50, and is identical in size and function but will not swell if exposed to high-aromatic 100LL or G100UL gas and lasts 10x as long, and will not deform if exposed to high pressure, I would happily pay you or another A&P/IA to research that and install the superior product. Maybe just me, but there's one data point.

The bigger question is why should we replace parts and do maintenance, some very intrusive and time consuming, to use a different fuel? This should be a straight replacement with zero maintenance required other than ongoing. Why do we as aircraft owners and mechanics have to continue to bear the cost of this? It’s a sure way to kill off more of GA all in the name of safety again. I like Mike Rowe’d safety third more and more every day. 

[A64Pilot]

1 hour ago, T. Peterson said:

Much discussion of the effects of G100 on components. What about our bodies? Wasn’t the whole driver of replacing 100LL a search for something that would not kill the little chilren?? So the new stuff melts paint, swells rubber and not a word about the lil chilren?? I don’t want to touch the stuff, much less put it in my airplane!

When I joined the Army as an aircraft mechanic in 1982, we used Acetone regularly to wash parts.

Eventually due to testing done and the results of what Acetone’s effects on the body was it was prohibited and replaced with Methyl Ethyel Keytone.

Then years later due to testing that showed that MEK was bad for you it was replaced by Methyl Iso Ketone. MIK

Now I’m pretty sure but can’t prove that in truth Acetone was the least “bad” of the three and while maybe well intended in truth the replacements were in fact worse than the chemical they replaced.

Its my understanding that aeromatics are bad stuff health wise, at least if you search aeromatics effects in auto fuel that seems to be the general belief.

[MikeOH]

2 hours ago, T. Peterson said:

Much discussion of the effects of G100 on components. What about our bodies? Wasn’t the whole driver of replacing 100LL a search for something that would not kill the little chilren?? So the new stuff melts paint, swells rubber and not a word about the lil chilren?? I don’t want to touch the stuff, much less put it in my airplane!

Nah, the new stuff just kills rich airplane pilots; the children are safe, so it's all good

[Fly Boomer]

8 hours ago, A64Pilot said:

As far as the recommendation to upgrade the rubber in the fuel system, yeah that’s worrisome, but it could be argued as simply good advice too Viton where allowed and Teflon lines are superior products from my experience. O-rings etc could cause serious problems even engine failures, but I think the biggest $$$ concern is bladders and fuel tanks.

Another material that gets used frequently these days for our fuel caps is known by its chemical name (fluorosilicone).  Not sure how it compares to Viton.  Seems silly to replace the old rubber o-rings every year or risk water in your fuel.  Also, I wonder if o-rings are less likely to swell in situ where they are somewhat constrained vs floating in a bath of hydrocarbons.

[PT20J]

15 minutes ago, Fly Boomer said:

Another material that gets used frequently these days for our fuel caps is known by its chemical name (fluorosilicone).  Not sure how it compares to Viton.  Seems silly to replace the old rubber o-rings every year or risk water in your fuel.  Also, I wonder if o-rings are less likely to swell in situ where they are somewhat constrained vs floating in a bath of hydrocarbons.

From https://www.marcorubber.com/Fluorosilicone-vs-FKM/material-type/11v10

Fluorosilicone vs FKM (Viton)

Both materials are well suited for use in the -30 to 180°C range. Fluorosilicone has an advantage in lower temperatures and FKM has an advantage in higher temperatures. Marco offers specific compound formulations extending these ranges even futher as can be seen in the following compound comparison chart. When comparing these materials with respect to electrical current resistance, Fluorosilicone has a slight advantage. The differences in compression set resistence show that FKM has a significant advantage. Additionally, FKM has a significant advantage when considering wear resistance. Also, both materials are equally poor when comparing heat stability. Furthermore, both materials are equally Fair when comparing short term resilience. Finally, FKM has a significant advantage when evaluating differences in permeation resilience. Both materials are resistant to ozone, compression set, common fuels, vegetable oils, aromatic hydrocarbons, chlorinated hydrocarbons, aging and silicone oils, with Fluorosilicone having specific resistences to weathering and sunlight, oxidizing chemicals, animal oils, chlorinated solvents, diluted alkalies, diester oils, aliphatic fluorocarbons, aromatic fluorocarbons, toluene, benzene, jet fuels, phosphate esters, dry heat, wide temperature range, ammonia, some acids and some petroleum oils. FKM has specific resistence to steam, solvents, broad spectrum chemical resistance, mineral oils, greases, aliphatic hydrocarbons, non-flammable hydraulic fluids, strong acids, petroleum oils, brake fluids, acetone, halogenated hydrocarbons, di-ester lubricants, vacuum and most acids.

[Marc_B]

Why did the fuel industry use toluene (for lots of different fuels) and why did GAMI feel it was better option for them to use xylene?  Would be interesting to learn how the fuel was developed…did GAMI trial toluene and various combinations of xylene and toluene?

From what I understand, toluene has higher octane rating and better performance as octane booster.  It is more volatile/higher evaporation rate so better cold start. Plus it is commonly used in unleaded high octane race fuel.

Xylene has a longer evaporation time/less volatile and is slightly less aggressive solvent but lower octane rating.

But I think the difference is much higher concentration of xylene and I’m curious how composition of G100UL changes as certain components evaporate increasing concentration of solvents with longer evaporation time with xylene.

Of course if you listen to Swift, their finger points at the meta-toluidine and aromatic amines as the reason for issues with paint and elastomers.

When mixing 100LL depending on the quality of the lead refining they were limited in total amount of lead so they’d test octane in the knock lab and add more toluene to meet spec to prevent knocking. So there was potentially less toluene than the 29% noted by Mr. Braly, but it varied.

What concentration of toluene would lead to damage to paint and elastomers that have been noted vs the concentration of xylene vs the composition of G100UL.

Would love to just sit down with Mr. Braly and an industry chemical engineer specializing in fuel over beers for a master class.

Seems like a matter of cons for each choice and some with lesser and some with greater problems.  Of course these are the things you wish key players shared info and actually worked together. But oil and gas is such a giant industry and everyone has a vested self interest and the 100LL segment is tiny but with a good profit margin as far as fuels go.

Industry doesn’t change quick as it’s not in their best interest so it’s politically motivated rather than self directed. Chess. 

[gevertex]

On 12/24/2024 at 7:47 AM, AJ88V said:

Thank you, @Marc_B.  No idea how you found the video, since a straight search on YT by title failed to pull it up.  

Here's the direct link:  https://www.youtube.com/watch?v=sPeQ6T3vB2E

Outstanding service to the aviation community by YT poster mluvara.  Comments are turned off, but recommend you go to the source and give it a thumbs up.

 

 

I was looking forward to G100 personally, but that's pretty damming stuff. Paint stripping is concerning enough, but o-ring swelling? That's bad news bears and reeks of the cheap transmission repair stuff you can buy at autozone.

Is the 8 octane difference between 92 mogas and 100 octane needed for our engines really so complicated that we need to basically put paint stripper in our tanks?

[McMooney]

22 minutes ago, gevertex said:

I was looking forward to G100 personally, but that's pretty damming stuff. Paint stripping is concerning enough, but o-ring swelling? That's bad news bears and reeks of the cheap transmission repair stuff you can buy at autozone.

Is the 8 octane difference between 92 mogas and 100 octane needed for our engines really so complicated that we need to basically put paint stripper in our tanks?

my poh says  never use aviation fuel of a lower grade than 91/96, i'm guessing it can be made to run on 94ul.

[Shiroyuki]

3 hours ago, PT20J said:

From https://www.marcorubber.com/Fluorosilicone-vs-FKM/material-type/11v10

Fluorosilicone vs FKM (Viton)

Both materials are well suited for use in the -30 to 180°C range. Fluorosilicone has an advantage in lower temperatures and FKM has an advantage in higher temperatures. Marco offers specific compound formulations extending these ranges even futher as can be seen in the following compound comparison chart. When comparing these materials with respect to electrical current resistance, Fluorosilicone has a slight advantage. The differences in compression set resistence show that FKM has a significant advantage. Additionally, FKM has a significant advantage when considering wear resistance. Also, both materials are equally poor when comparing heat stability. Furthermore, both materials are equally Fair when comparing short term resilience. Finally, FKM has a significant advantage when evaluating differences in permeation resilience. Both materials are resistant to ozone, compression set, common fuels, vegetable oils, aromatic hydrocarbons, chlorinated hydrocarbons, aging and silicone oils, with Fluorosilicone having specific resistences to weathering and sunlight, oxidizing chemicals, animal oils, chlorinated solvents, diluted alkalies, diester oils, aliphatic fluorocarbons, aromatic fluorocarbons, toluene, benzene, jet fuels, phosphate esters, dry heat, wide temperature range, ammonia, some acids and some petroleum oils. FKM has specific resistence to steam, solvents, broad spectrum chemical resistance, mineral oils, greases, aliphatic hydrocarbons, non-flammable hydraulic fluids, strong acids, petroleum oils, brake fluids, acetone, halogenated hydrocarbons, di-ester lubricants, vacuum and most acids.

Only as low as -30? Now I will have a problem... It is colder then -30 from time to time here in winter....

[Fly Boomer]

@PT20J I didn’t notice “swelling” in the comparison you posted. Is “permeation resilience” the code phrase for “swelling”?

[tony]

22 hours ago, A64Pilot said:

I’ve done hot fuel testing, it’s an airframe requirement, not I believe a fuel requirement.

 

My point exactly.  so how can the FAA issue an STC for the type design of an airframe?

[Pinecone]

On 12/24/2024 at 1:23 PM, MikeOH said:

I will say, your ability to turn your eyes away from that video is quite impressive!  As even @GeeBee said, "That is some disturbing results"... yet you soldier on with no concerns; amazing!

Did you see the other post that GAMI is aware of the O-ring swelling, but that it does not affect operation?   And may even help worn O-rings seal again?

It is not like the O-rings are being eaten away.