G100UL - fuel leak

[ragedracer1977]

23 minutes ago, MikeOH said:

Which is pretty close to 20,000,000

Any guesses why someone would want their product to be the sole source?

 Out of curiosity, does anyone know how much G100UL has been sold at RHV?  
 

It might dampen my worries if it’s 20 or 30k gallons over the last few months and we’re just seeing extreme outliers

 

[MikeOH]

2 minutes ago, ragedracer1977 said:

Any guesses why someone would want their product to be the sole source?

 Out of curiosity, does anyone know how much G100UL has been sold at RHV?  
 

It might dampen my worries if it’s 20 or 30k gallons over the last few months and we’re just seeing extreme outliers

 

Just think what a ban on sales of 100LL would do for sales of a sole source product

Regardless of quantity sold, a couple of months is just not enough time to observe long term effects (think O-ring failures, valve recession, etc.)

[UteM20F]

11 hours ago, ragedracer1977 said:

 Out of curiosity, does anyone know how much G100UL has been sold at RHV?  

As of Dec 4, RHV had received 2 tanker loads (~7500 gallons each) of G100UL.  This is sourced from the Consent Decree lawsuit that was posted above.  Interestingly, the same document claims RHV paid about $5.50 / gallon for that fuel, which included the price of transporting it.

[PT20J]

There seems to be consensus that up to about 30% volume change is permissible in a static o-ring. The video showed an 8-10% change in diameter. Assuming that the swelling causes an equal dimensional change in all directions, a 30% volume increase would cause a about a 10% circumference increase. The diameter being proportional to the circumference would also increase by 10%. Therefore the swelling appears to be at the upper end of the acceptable range for a static o-ring application and exceeds the acceptable range for a dynamic application.

I am not saying (nor have I said previously) that this is acceptable because I do not know whether it causes a problem in service or not. 

[George Braly]

On 12/28/2024 at 6:04 PM, Marc_B said:

@George Braly out of curiosity, do you have a link to the Allied Signal/Bendix service document you're referring to (I'm not familiar)?  I'm also curious if the G100UL fuel you show tested in the picture is from the same batch and composition that was sold in California?  If it was different batch, how did the Baton Rouge sample differ from KRHV sample (how did the overall aromatic percentage differ)?  Has GAMI tested this fuel to see if there were any contaminants or issues in the field?

The G100UL SDS is pretty broad; how much does one batch of G100UL composition vary from another?

Also what was the thought of "high toluene" vs 15% toluene and what was the amount of toluene in the "high" sample?

Thanks for your help to understand this all.

https://precisionairmotive.com/wp-content/uploads/2019/06/RS-76-Rev1.pdf

1) That  link  to allied signal / Bendix was posted in another message, but it is copy / pasted here for convenience. 

I think the "take away" from that 44+ year old document is that there has been a recognized industry effort to eliminate nitrile components from aircraft fuel systems that goes back nearly half a century.   Unfortunately, compliance by portions of the industry has been less than robust.   We required removal of rubber / nitrile fuel hoses from all of the TAT Turbo systems some 20 years ago, and replacement with teflon lined hoses.   

2) Yes.  The fuel used for that soaking is from the same batch produced in Baton Rouge that was sent to California.

3) Yes.   We run DHAs (Detailed Hydrocarbon Analysis) per ASTM D6700 or D6733  (basically Gas Chromatograph technology) on every fuel batch produced.  That will typically detail every molecule that shows up with a concentration > ~ 0.01%.   If there were any contamination it would show up on the DHA. 

4) The SDS for 100LL and G100UL is extremely broad.    That is true of almost all types of fuels.   The control of the actual quality of the fuel is pretty much unrelated to the SDS.   The control actually takes place in the FAA approved specification - -  not in the SDS.   The FAA approved G100UL avgas specification is much (very much) tighter controlled than is the ASTM D910 specification for 100LL.  

5) Depending on the refinery producing the batch of 100LL,  there can be as little as about 15% toluene, to as much as 29% toluene (by mass fraction - - m/m).    We added the extra toluene to our local FBO 100LL in order to make sure we had a "boundary condition" on upper toluene included in the paint testing.   

[Marc_B]

I think the sticky point is that 1) there's a possibility that G100UL affects sealant and elastomers similar to 100LL, 2) possibility that effects are more than 100LL due to a higher total aromatic concentration.

But I think that it's likely that a) G100UL may have different effect on elastomers such as Nitrile and b) that higher amounts of nitrile material may be found in older airframes, coupled with the fact that nitrile elastomers have a shorter service life than fluorosilicone/viton.  So the ambiguity is that the evidence of deterioration in general is leaking and the confounder is whether it's the age of the sealant/o-ring/elastomer vs. the effects of G100UL.

It also could be that old sealant and nitrile are just more sensitive to a higher aromatic fuel, or it's just old and needs to be replaced.

But this will require more data and pointed studies from GAMI to help clarify which materials and product age are problematic.  Otherwise you could point to either the age/quality of the product or the affect of the fuel and you'd probably both be right.

This is why I feel that more clear instructions in an ICA would be helpful.  But it's certainly possible we just don't have that data yet and current recommendations are about the most we know for now.

[George Braly]

On 12/29/2024 at 7:56 AM, takair said:

@George Braly, with all this talk of sealants and orings, my mind jumps to the internal regulating diaphragms in our fuel injection systems.  I can’t find the material type in my limited reference material.  Was GAMI able to determine this or do testing to ensure no long term degradation of performance of these diaphragms?

Yes.   That was included as part of the very first testing we did for the FAA related to material compatibility.   The FAA required us to create an elaborate "rig" test.   That operational rig test included essentially all of the fuel system components from both Lycoming and Continental engine  and related aircraft systems. 

A partial list of OEM components (used condition) tested include:

1) Lycoming fuel pump;  2) Continental fuel pump;  3) fuel spiders (with the diaphragms) for both Lyc & TCM) ;  4) a couple of different AC fuel selectors;   5) various check valves;  6) fuel injectors;  fuel lines of various materials;  7) three different fuel bladders - -  1954 ;  ~  1980;  and 1985 year models;     and a lot more.

The fuel pumps were electrically driven but were heated with electric heaters so they operated at engine operating temperatures.

That "operational"  or 'dynamic'  testing continued for a period of about nine months.   The FAA randomly came by to inspect the testing in progress. 

PAFI people saw a presentation on the dynamic test rig at an ASTM meeting and really liked it.  They asked for a copy of the drawings and test plan which we provided. 

Note:  One thing we have learned recently,  those diaphragms are sensitive to oxygenates - - such as ETBE.  

We had several similar diaphragms fail after short exposures to ETBE based fuel chemistries when we were doing some comparison testing on our test stand.   

Again, let me know if you have more questions. 

[George Braly]

On 12/29/2024 at 10:04 AM, gabez said:

top of my wings...permanently stained by G100. Unfortunately my plane hasn't hit the shop yet, they have been super busy and they don't have space in the hanger yet. I hope this coming week. 

The pain peeling has gone a bit worst. The leak seems to be confined in the Copilot Aux, however a paint buy a rivet in the co-aux popped as well as the paint on a rivet in the pilot main. 

Help me understand, how did the fuel get to those spots on the top of the wing ?  

When was the plane last painted ?  

And last, I think it is likely those brown spots will polish out.  Not positive.  But we have done that as an experiment using fuel we deliberately spilled on painted aircraft parts, and which we allowed to dry for several days.  It takes some elbow grease and a series of polishing compounds to make that work.

 

[George Braly]

On 12/29/2024 at 10:02 AM, Fly Boomer said:

If you are concerned about putting phony parts on your certified airplane, you should stick to nitrile o-rings.

The ICAs for G100UL Avgas are data acceptable to the administrator that authorize the substitution.  In addition, these types of changes are classified by the FAA as  "minor changes" .

It is my understanding, from a lunch conversation with Mike Busch, yesterday, that they only require "acceptable data" upon which the mechanic can rely.   However, I want to investigate the subject some more when we get through some of the higher priority items. 

[gabez]

10 minutes ago, George Braly said:

Help me understand, how did the fuel get to those spots on the top of the wing ?  

When was the plane last painted ?  

And last, I think it is likely those brown spots will polish out.  Not positive.  But we have done that as an experiment using fuel we deliberately spilled on painted aircraft parts, and which we allowed to dry for several days.  It takes some elbow grease and a series of polishing compounds to make that work.

 

you just move the nozzle from the aux port to the main port and it drips sometimes

painted in 1984

w/100UL I don't have to worry about staining nor having worry about the nozzle 

[Pinecone]

15 hours ago, MikeOH said:

Not at this moment.  But, here in Kalifornia (coming soon to the rest of country) the plan is to soon BAN 100LL.  At that point, yes, we will be FORCED to buy G100UL if no other unleaded fuel is available to compete.  If banning of 100LL wasn't an issue I wouldn't even participate in this debate.  Buy, don't buy, we should be free to choose.

But that is NOT on GAMI.  Maybe Swift will be able to expand their STC and you will have a choice.

Or, you can stop flying.  But again, not on GAMI.

[Sabremech]

1 hour ago, George Braly said:

The ICAs for G100UL Avgas are data acceptable to the administrator that authorize the substitution.  In addition, these types of changes are classified by the FAA as  "minor changes" .

It is my understanding, from a lunch conversation with Mike Busch, yesterday, that they only require "acceptable data" upon which the mechanic can rely.   However, I want to investigate the subject some more when we get through some of the higher priority items. 

As an A&P / IA, it’s not up to me to make substitutions on the materials used to make an o-ring. It’s up to the manufacturers of those parts to change the material. I strictly work off of what’s in the IPC for the aircraft I’m working on. I can tell you other than looking at the P/N and  the cure date, I don’t look for what it’s made out of. 
 You’re putting mechanics in jeopardy by coming up with substitutions and acceptable data. Something goes wrong, and we’re left to hang. I understand what you’re trying to do and applaud you for it. What I don’t like is putting more onus on mechanics with gray areas for us to have to muddle through. 
Thanks,

David

[MikeOH]

38 minutes ago, Pinecone said:

But that is NOT on GAMI.  Maybe Swift will be able to expand their STC and you will have a choice.

Or, you can stop flying.  But again, not on GAMI.

Where have I said that I was blaming being forced to buy G100UL on GAMI??
THAT is the fault of an overreaching government.

[Pinecone]

That we agree on.  But it is coming.  And the good thing is, we have a larger, but still limited test, versus having no fuel in 2031 and having to accept whatever anyone offers.

[Pinecone]

19 hours ago, Sabremech said:

As an A&P / IA, it’s not up to me to make substitutions on the materials used to make an o-ring. It’s up to the manufacturers of those parts to change the material. I strictly work off of what’s in the IPC for the aircraft I’m working on. I can tell you other than looking at the P/N and  the cure date, I don’t look for what it’s made out of. 
 You’re putting mechanics in jeopardy by coming up with substitutions and acceptable data. Something goes wrong, and we’re left to hang. I understand what you’re trying to do and applaud you for it. What I don’t like is putting more onus on mechanics with gray areas for us to have to muddle through. 
Thanks,

David

Someone pointed out, that Texton is selling Viton or Flourosilicone O-rings, if you order from them.  As the standard ones.  So you may have been installing them already.

They are part of the group that has been trying to get Nitrile out of airplanes for 50 years.

[Pinecone]

I don't know where it is, but someone posted on one of these threads that the current O-rings sold by Textron are Viton or flourosilicone.

[Pinecone]

This was posted by Jet Driven and shows why no amount of testing of ANY fuel will cover all the possible issues that result in leaks.

"We do patch wing tank fuel leaks occasionally. You'd be surprised the crap we see. People use non-approved sealants, or they dont mix the approved sealant properly.  They dont prep the work, they dont find the leak, they smear it with their gloved fingers. We recently fixed a wing tank that the client paid amost 3K to a well known east coast MSC.  The sealant was light gray and it was gooey like putty, it was the wrong stuff, not mixed right, or both. The tank was leaking again after half a year.  We've got a 177 Cardinal in our shop right now actually, it was leaking from the outboard corner of the wing tank, the owner is working with us on this, he pulled the top cover off, was sealed with orange RTV and it was gooey and smearing off because it's not supposed to be there, the end board corner of the tank had at least two different kinds of crap smeared all over it, and it was leaking underneath that. After spending the better part of two days, stripping and scraping and stripping and scraping, it's cleaned up enough where we can probably put sealant on it now.  Point being, sometimes properly and accurately fixing a wet tank Mooney leak can get very expensive. One client just paid nearly 30 grand to get his 100 gallon tanks stripped and resealed.   Prayer is not a strategy. I'm not saying take your plane to O&N and have bladders put in it, but I would say that if the plane has bladders and they're not leaking, that is one $20-$30,000 repair job you're probably not gonna have to ever worry about. 

 

[EricJ]

30 minutes ago, Pinecone said:

Someone pointed out, that Texton is selling Viton or Flourosilicone O-rings, if you order from them.  As the standard ones.  So you may have been installing them already.

They are part of the group that has been trying to get Nitrile out of airplanes for 50 years.

You may have missed where a C310 owner posted here that they just replaced some fuel system o-rings ordered from Textron and got nitrile.   There are applications where the properties of nitrile may still be preferred over other materials.

Hoses are also an issue since many fuel hoses are nitrile.   Swelling degrades the strength and longevity, so hose failures may be latent with formulations that cause excessive swelling.   

[Pinecone]

And have any issues been reported?

GAMI tested in a number of aircraft for over 10 years.  RHV has been pumping it for 2 months now.

And no reported issues that I have seen.

If you have some O-rings handy, test them in 100LL and show how much they swell when just dropped in fuel.

[Schllc]

On 12/30/2024 at 12:08 AM, MikeOH said:

Which is pretty close to 20,000,000

this is a curious number for me.  if you look at the FAA website there is about 180k registered pistons in the US. 

If you use this website it says that in 2020 there was 412k gal per day.  if you divide that by the fleet, and divide that by an average of 15gph that is 55 hours per plane on average per year.  I suppose it could be true, but that sounds awfully optimistic considering 30k are experimental/light sport, and all the hangar queens...  i wonder how much is law enforcement and military

[Aaviationist]

20 hours ago, Sabremech said:

As an A&P / IA, it’s not up to me to make substitutions on the materials used to make an o-ring. It’s up to the manufacturers of those parts to change the material. I strictly work off of what’s in the IPC for the aircraft I’m working on. I can tell you other than looking at the P/N and  the cure date, I don’t look for what it’s made out of. 
 You’re putting mechanics in jeopardy by coming up with substitutions and acceptable data. Something goes wrong, and we’re left to hang. I understand what you’re trying to do and applaud you for it. What I don’t like is putting more onus on mechanics with gray areas for us to have to muddle through. 
Thanks,

David

Tell us what shop this is so we can never go there. 
 

you want Mooney, a company that barely exists, to go back and update a manual they haven’t updated in many decades to include a material for o rings, which have been being used also for decades?

 

nobody is putting you at risk. It’s perfectly acceptable to use a print that meets or exceeds the original.  You’re either very difficult mechanic to work with, or, just looking for an argument. 

[EricJ]

23 hours ago, PT20J said:

There seems to be consensus that up to about 30% volume change is permissible in a static o-ring. The video showed an 8-10% change in diameter. Assuming that the swelling causes an equal dimensional change in all directions, a 30% volume increase would cause a about a 10% circumference increase. The diameter being proportional to the circumference would also increase by 10%. Therefore the swelling appears to be at the upper end of the acceptable range for a static o-ring application and exceeds the acceptable range for a dynamic application.

I am not saying (nor have I said previously) that this is acceptable because I do not know whether it causes a problem in service or not. 

I used a couple different techniques to estimate the dimensions of the o-rings in the vid, and once I got them consistent with each other and the measurements shown, I computed the volumes of each.    The best way to estimate swelling would be to use the dimensions of the rings before the testing as the initial state, but that isn't given.   Using the specs for the rings at the initial condition instead I got 32%, 35% and 30% swelling for the o-rings in G100UL using just the i.d. and o.d. dimensions for the volume estimate.   I got zero swelling or shrinkage for the 100LL rings, which is unlikely and suggests that they may have started at the lower ends of the dimensional tolerance rather than the middle.   That suggests that the swelling estimates for the G100UL rings may be underestimated.
 

[Sabremech]

4 hours ago, Pinecone said:

Someone pointed out, that Texton is selling Viton or Flourosilicone O-rings, if you order from them.  As the standard ones.  So you may have been installing them already.

They are part of the group that has been trying to get Nitrile out of airplanes for 50 years.

They, along with aircraft manufacturers, are who should be working with the seal manufacturers to change the compounds that are used. It’s not up to me or any other mechanic to search out an alternate p/n to switch to viton, etc. I may very well have been installing them but again don’t specifically look at the compound they are made of. Part number and cure date are the main things I look for.  As I stated previously, this also has the real potential for intrusive maintenance which we all know can turn quite expensive quickly. 
I hope that other true direct replacement fuels come to market that don’t have the reported issues this fuel may have. 
Thanks

[PT20J]

If I understand correctly, the FAA required GAMI to run tests to show G100UL compatibility with fuel system components before it approved the STC. I haven’t seen the ICA, but if there are no airworthiness limitations (which the FAA would  have had to approve) requiring changing components to a different material, then there is no requirement to do so. 

Details of the testing are coming out in dribs and drabs in posts on the forums. Perhaps it would answer a lot of questions we have about the risks to our fuel systems if @George Braly would make the test details and results available as well as any formal approval documentation from the FAA.

[donkaye]

The FAA provides approval of STCs.  They provide approval for the certification of our airplanes. They took over 12 years to approve this STC.  They are strict in their approval process.  Every time I get in my airplane I am depending on the Avionics, the design details of which I am not familiar; the engine, the design details of which I am not familiar; the manufacturer of all the components,  the designs of which I am not familiar; the fuel, the design of which I am not competent to render a judgement on.  I am a pilot and I know how to fly an airplane.  How an airplane is made and it components, while interesting, I leave to the experts.  Based on past history, I am willing to trust the experts.  Do I like that G100UL stains paint? No, but mitigation was described in the paperwork that came with the STC.  I think the fuelers need better instructions including use of their wing "protector", that I think caused my issue.

Do the people who have commented on these threads commit the time to investigate every component on their airplane? I think not.  As an example, we trust our Avionics without question, don't ask to look into the software to see if we can find a problem.  We blindly read the manuals and assume it will work as published.  We use the avionics and from time to time find flaws in it.  I have found and communicated flaws in the Aera 796 and 760, and even the G500TXi, for example.  Garmin for the most part has fixed them.  Avionics issues could harm us quicker (and has with failed vacuum pumps in the past) than this fuel issue being discussed ad nauseam.  Much of what is being said, and my not being an A&P, is incomprehensible to me.  Bottom line to me is if you want the benefits of unleaded fuel with some caveats use it, and if, not, don't.

That being said, Happy New Year.