FAA To Approve Use Of 91UL Fuel In Two-Thirds Of Piston Fleet

asicer said:
Wait, were we talking about unleaded avgas? Or the Petersen autogas STC?
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Thread drift. Shep brought autogas into the discussion. I was just using that as an example to show that the Lycoming document is insufficient by itself.
 
My Warrior with an O-320-D3G engine does have a Petersen mogas STC. It requires significant modifications to the fuel system and I do not know of a single non-corn-liquored-up mogas in my area.
 
My plane is the only one of its type in the entire world that is approved for non-alcohol premium auto fuel, it was done by a previous owner under a field approval, but I haven’t seen eligible non-alcohol fuel at the pump in many years. I know it’s out there somewhere in the US but nowhere I go, even miles from the airport.

100LL without the lead would be ideal for my 80/87 certified O-320, and I’d be also be interested in knowing for sure whether this means 91UL or 94UL so I could look out for it. Avgas is such wonderful fuel in terms of its storage life and lack of awful stench, I’d much rather use it than mogas, and just leaving the lead out of 100LL would make the perfect fuel for my purposes.
 
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^^^ Yep, mine too.
 
I have the STC for UL 94 ,problem is ,it’s not widely available. Also price point is higher than 100 LL.
 
Half Fast said:
Note that a fuel can be approved for an engine but not approved for a particular plane, due to issues with the fuel storage and delivery system. The table in this document shows that my O360 can run on anything this side of Jack Daniels, but mogas is not approved for my Beech (I believe there was a vaporization problem).

EDITED TO ADD:
Just found this - “The airframes we have flight tested which failed the test include the Navion, Musketeer, Piper Apache PA-23-235, 7KCAB, Mooney M-20-C, Piper PA-24 250 Comanche & the Avcon converted 180 hp Cessna 172. Generally speaking, any pump fed airplane not already on the approved list is incapable of passing the flight tests unless substantial modifications are made.”
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What is the issue with 'pump fed'? Are they trying to make a blanket statement that any engine driven pump fed airplane can't use it?

If so, that isn't a correct statement.

Both of my airplanes (Beech 18 and T6) will be able to use the newer fuels if necessary and they are both 'pump fed', but the engine shops have been telling us to not expect to make TBO.
 
You'll have to make some choices....advance the timing and lose power or leave things as they are and run hotter CHTs. There is no free lunch.

Or pays the extra and run 100LL.
 
chemgeek said:
91UL is basically 100LL without the TEL additive, so it should meet the fuel specifications for aircraft that do not require 100 octane fuel. G100UL took the (necessary) approach of dispensing with the existing fuel specification in order to achieve the desired result of serving the entire piston fleet.
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No, 94UL is 100LL without the TEL.

91UL is a mogas based fuel.
 
Half Fast said:
Thread drift. Shep brought autogas into the discussion. I was just using that as an example to show that the Lycoming document is insufficient by itself.
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Interestingly, EASA says that you can use UL91 (the avgas, not mogas) if the engine is approved whether the airframe TCDS says so or not.
https://www.easa.europa.eu/en/faq/19380

Perhaps the FAA is just exercising some reciprocity?

And oh by the way, Textron has this to say about UL91 and your baby Beech (yours is 180hp right?):
https://web.archive.org/web/2022020...custsupt/contacts/pubs/ourpdf.pdf?as_id=54042
 
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Mongoose Aviator said:
Are Turbo equipped aircraft covered under the auto fuel STC or is this non-Turbo only?
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Non-turbo and low compression only.

Most all O-320 can run on 91 (originally certified for use 91/96 grade or 80/87). Some can run on mogas.

O-360 180 HP, except O-360-Exx can run on 91. But all IO-360s require 100.
 
Domenick said:
My Warrior with an O-320-D3G engine does have a Petersen mogas STC. It requires significant modifications to the fuel system and I do not know of a single non-corn-liquored-up mogas in my area.
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KAWO and KOKH used to have 91 octane mogas, but it's been several years since I've seen it.
 
Kenny Phillips said:
To be approved, it can be no worse than today's 100LL. Vapor lock is very configuration specific.
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That's kinda the answer I found to my Vapor Lock concerns. It took over 10 years for GAMI to prove their vapor lock test. The auto STC required quite a bit of vapor lock testing. Many low wing aircraft require a fuel circulation system if using auto fuel.

Question is where's the FAA data on vapor lock probability with 91UL?
 
asicer said:
Interestingly, EASA says that you can use UL91 (the avgas, not mogas) if the engine is approved whether the airframe TCDS says so or not.
https://www.easa.europa.eu/en/faq/19380

Perhaps the FAA is just exercising some reciprocity?

And oh by the way, Textron has this to say about UL91 and your baby Beech (yours is 180hp right?):
https://web.archive.org/web/2022020...custsupt/contacts/pubs/ourpdf.pdf?as_id=54042
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Heck, my original type certificate says "91/96 minimum grade aviation gasoline." As far as I can tell, I can use a 91UL fuel that has been approved as aviation gasoline by the FAA, no STC required. (But not mogas.)
 
As I understand it, 91UL is based on mogas, but is not the same mogas you get at a pump. It has a specific volatility range, like AVGAS.

"Compared to Mogas, it has an assured energy content with no alcohols or ethers which may reduce aircraft range. It has a fixed volatility range and is designed to work year-round without seasonal variations. It is better for your aircraft as it contains no ethanol which can damage aircraft fuel system components."

"Aviation gasoline UL 91 meets the requirements of ASTM D 7547 and DEF STAN 91-90."
 
Klaus M said:
That's kinda the answer I found to my Vapor Lock concerns. It took over 10 years for GAMI to prove their vapor lock test. The auto STC required quite a bit of vapor lock testing. Many low wing aircraft require a fuel circulation system if using auto fuel.

Question is where's the FAA data on vapor lock probability with 91UL?
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91UL is blended to a specific vapor pressure year round. LIke AVGAS.

It IS AVGAS, but blended from MOGAS base stocks.
 
Half Fast said:
Heck, my original type certificate says "91/96 minimum grade aviation gasoline." As far as I can tell, I can use a 91UL fuel that has been approved as aviation gasoline by the FAA, no STC required. (But not mogas.)
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Thanks for the tip to check my TCDS. Piper Warrior II (PA-28-161): 100 octane minimum grade aviation gasoline

Damn!
 
Tusayan said:
My plane is the only one of its type in the entire world that is approved for non-alcohol premium auto fuel, it was done by a previous owner under a field approval, but I haven’t seen eligible non-alcohol fuel at the pump in many years. I know it’s out there somewhere in the US but nowhere I go, even miles from the airport.

100LL without the lead would be ideal for my 80/87 certified O-320, and I’d be also be interested in knowing for sure whether this means 91UL or 94UL so I could look out for it. Avgas is such wonderful fuel in terms of its storage life and lack of awful stench, I’d much rather use it than mogas, and just leaving the lead out of 100LL would make the perfect fuel for my purposes.
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The closest 3 stations to me all have E0.
 
FPK1 said:
And neither Textron, Piper, CubCrafters, nor Lycoming have tested any of the new fuels yet... What?!
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Its not their place to have to "test" the new fuels. Nor do I blame them. The debate on pursuing new fuels via the STC process vs the specification process has been ongoing for years. Its the reason GAMI went the STC route and developed their own certification procedure because they didn't want to wait. However unless they revise the current D910 spec to include unleaded fuel there will still need to be a revision in some form to all the existing type certificates on a global scale.
 
I've been told a couple times that the reason a given FBO had mogas available was because they used it for maintenance purposes for mowers, cars, etc. Maybe more will be pushed over the edge and stock it if 2/3rds of the fleet can run on it also?
 
Bell206 said:
However unless they revise the current D910 spec to include unleaded fuel there will still need to be a revision in some form to all the existing type certificates on a global scale.
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I've wondered about this. I think you're likely correct, but I don't understand the regulatory mechanism.

My type certificate doesn't refer to the D910 (or any other) spec, and it doesn't say the fuel must contain TEL. It simply says "91/96 minimum grade aviation gasoline." At first glance, it would seem to me that any avgas which satisfied the octane requirement would be compliant with the type certificate. Why must the type certificate change?
 
Half Fast said:
My type certificate doesn't refer to the D910 (or any other) spec, and it doesn't say the fuel must contain TEL. It simply says "91/96 minimum grade aviation gasoline." At first glance, it would seem to me that any avgas which satisfied the octane requirement would be compliant with the type certificate. Why must the type certificate change?
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I presume the regulatory definition of "aviation gasoline" means "gasoline that meets D910".

My T-Craft required 73 octane minimum.
 
Dana said:
I presume the regulatory definition of "aviation gasoline" means "gasoline that meets D910".

My T-Craft required 73 octane minimum.
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I would think so, but so far I haven't been able to find that "regulatory definition."
 
Half Fast said:
Why must the type certificate change?
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In general, when most of the current operating aircraft were certified via CAR3 or Part 23 there was a requirement to determine the minimum fuel grade per 3.747 and 23.1521. The TCDS is merely a summary of the certification conditions and limitations and is not directly applicable to what specific specifications/standards were used to determines those fuel grades during the certification process. Those are listed in the actual type design. So, in general again, the standard/specification used to meet 3.747 or 23.1521 were either one of the old MIL-SPECs or ASTM D910. Its this point that drives the requirement for an STC or ATC to be used for unleaded avgas. There was a similar issue when the 1st multi-grade oil was introduced which also required an STC until a revision was made to the original oil grade certification specification. There are several existing ASTM specs on unleaded avgas however unless they revise the D910 to include those blends it will always require that additional approval step. If that makes sense to you.
 
Bell206 said:
In general, when most of the current operating aircraft were certified via CAR3 or Part 23 there was a requirement to determine the minimum fuel grade per 3.747 and 23.1521. The TCDS is merely a summary of the certification conditions and limitations and is not directly applicable to what specific specifications/standards were used to determines those fuel grades during the certification process. Those are listed in the actual type design. So, in general again, the standard/specification used to meet 3.747 or 23.1521 were either one of the old MIL-SPECs or ASTM D910. Its this point that drives the requirement for an STC or ATC to be used for unleaded avgas. There was a similar issue when the 1st multi-grade oil was introduced which also required an STC until a revision was made to the original oil grade certification specification. There are several existing ASTM specs on unleaded avgas however unless they revise the D910 to include those blends it will always require that additional approval step. If that makes sense to you.
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Thanks. That makes sense. So to really know the requirement, we'd have to see the actual type design documentation, but it's a pretty good assumption that it refers to D910.

Interesting point about the oil spec. Why isn't an STC needed to call out the latest revision of the spec, though?

I know in the aerospace world where I worked for many years, when we spec'd a missile or targeting system we always called out the exact issues of the milspecs we referenced; there was no guarantee whatsoever that a design would comply with later revisions.
 
Half Fast said:
Why isn't an STC needed to call out the latest revision of the spec, though?
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As noted, they revised the original spec to include multi-grade oils so no STC needed. Bottomline, in general terms, if they were to revise D910 to include unleaded avgas technically no further approval needed, i.e., a STC. However, this topic is a bit more complex than that when trying to discuss as there are international issues as well.
 
Bell206 said:
As noted, they revised the original spec to include multi-grade oils so no STC needed.
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You’re missing the meat of my question. Why wouldn’t an STC be needed to change a reference in the type design documentation from “D910” to read “D910 Rev A” or something similar? Otherwise it seems you’re only certified to Rev New.
 
Half Fast said:
You’re missing the meat of my question. Why wouldn’t an STC be needed to change a reference in the type design documentation from “D910” to read “D910 Rev A” or something similar? Otherwise it seems you’re only certified to Rev New.
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The current version of D0910 is 21, all previous revisions inactive. Updating the spec, or any spec for that matter, isn’t uncommon.

https://www.astm.org/d0910-21.html
 
Half Fast said:
Why wouldn’t an STC be needed to change a reference in the type design documentation from “D910” to read “D910 Rev A” or something similar?
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Perhaps lets try a different way. Its all about the hierarchy in certification: laws, regulations, standards - specifications, type certificates, etc. Standards affect all aircraft and STCs affect specific type certificates. Change the existing standard level and all aircraft are covered under the revised standard. Change at the TC level and every aircraft needs an STC.

Same if they develop an additional standard other than D910 it will require an STC. However there are regulatory administrative routes that can be used to apply a new standard to all aircraft but it is a very complex especially on a global scale. The primary issue over this is the aviation regulatory authorities do not create these stardards/specifications (MIL-SPEC, ASTM, SAE, etc) but are simply a consumer of these references during the certification process. Regardless keep in mind this is a very general explanation of this process.
 
rwellner98 said:
I've been told a couple times that the reason a given FBO had mogas available was because they used it for maintenance purposes for mowers, cars, etc. Maybe more will be pushed over the edge and stock it if 2/3rds of the fleet can run on it also?
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91UL is not actually mogas. It is a avgas, based on mogas formulations.

The places currently selling mogas, are selling the same ethanol free gas you buy at the gas stations. That is NOT 91UL. For instance, 91UL is blended to a specific vapor pressure year round.
 
Bell206 said:
In general, when most of the current operating aircraft were certified via CAR3 or Part 23 there was a requirement to determine the minimum fuel grade per 3.747 and 23.1521. The TCDS is merely a summary of the certification conditions and limitations and is not directly applicable to what specific specifications/standards were used to determines those fuel grades during the certification process. Those are listed in the actual type design. So, in general again, the standard/specification used to meet 3.747 or 23.1521 were either one of the old MIL-SPECs or ASTM D910. Its this point that drives the requirement for an STC or ATC to be used for unleaded avgas. There was a similar issue when the 1st multi-grade oil was introduced which also required an STC until a revision was made to the original oil grade certification specification. There are several existing ASTM specs on unleaded avgas however unless they revise the D910 to include those blends it will always require that additional approval step. If that makes sense to you.
Click to expand...

It seems the long term thing to do is pull all 100 grade aviation fuels under D910.
 
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