Unleaded Avgas
Risks & Reality
Michael Luvara
Airventure 2026
So, how did I end up here today?
About Me
Pilot, Engineer, & Aviation Enthusiast
BACKGROUND & EDUCATION
FLYING BACKGROUND
PROFESSIONAL EXPERIENCE
A Few Disclosures…
person
Personal Research
I’m here of my own accord, sharing personal research on the subject and it is not related to or connected to my day job
payments
Independently Conducted Testing
I’ve conducted this testing on my own and have funded it all myself
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Committed to a Safe & Smart Transition
I am committed to a safe and smart transition to unleaded fuels
The Transition to Unleaded Avgas
Removing lead to establish a sustainable 100-octane unleaded aviation gasoline
Three Major Players
GAMI
G100UL
Swift Fuels
100R + UL94
VP / LyondellBasell
UL100E
Presentation Outline
Discuss Risks & Reality of the Unleaded Avgas Transition
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California's Involvement
Tell a story about California’s involvement in the avgas transition journey.
science
Candidate Fuel Certification Process
Share my understanding of the candidate fuels and the fuel certification process
Material Testing & Lessons Learned
Lessons learned from the field (and my garage) with three unleaded candidates
auto_stories Help You Prepare
Provide you with information and resources to better understand how to prepare yourself and your aircraft for the transition.
So, let me tell you a story that involves
Airports are Under Numerous Threats
Santa Clara County Airports
local_airport
Reid Hillview Airport (KRHV)
San Jose, CA
Two 3100’ runways, Towered
~200,000 operations per year
local_airport
San Martin Airport (E16)
San Martin, CA
Single 3100’ Runway, Non-towered
~40,000 operations per year
Specific Threats to Reid Hillview (RHV)
RHV target of numerous threats to close it, with Lead being the latest
2018
Supervisors voted to cease taking federal funds in 2018
2021
It became apparent that the Lead topic was the latest target of airport opponents
Swift UL94 Arrives @ RHV - Aug 2021
Local pilots, FBOs and airport association proactively brought in Swift’s UL94
~70% FLEET COMPATIBILITY
Works with typical 4-cylinder, low-compression engines, but is not 100 octane.
COMMUNITY-LED INITIATIVE
Proactively brought in by local pilots, FBOs, and the airport association.
Statistical Blood Lead Level Study
August 4, 2021
Santa Clara County released a blood lead level study that they believe correlates causation of blood lead levels in children to avgas.
August 17, 2021 Board of Supervisors Meeting
“take all actions necessary to transition to carrying only lead free gas at both County airports as soon as possible with the understanding that the sales of leaded gas will not be permitted at either County airport after December 31, 2021 except for emergency operations.”
County Policy & Compliance
Lead Soil Study
STUDY & TRANSPARENCY
Buried Investigation
County spent $130k to drill and collect soil samples. The study was ‘buried’ until journalists uncovered it.
SOIL ANALYSIS
No Elevated Lead in Soil
Official testing confirmed there were no elevated lead levels found in the soil at either of the two county airports.
OFF-SITE IMPACT
Expressway Proximity
The highest lead levels were detected next to the expressway adjacent to the airport, rather than on airport grounds.
MEDIA UNCOVERED REPORTS
Let’s Pause and Discuss Fuel for a Bit
I’ll come back to the story…
Risks & Reality
The challenges and timelines of the unleaded avgas transition
schedule
Phase-Out Timeline
100LL is going away, with firm target dates established for the transition:
local_gas_station
The Drop-in Fuel Challenge
Finding a direct drop-in replacement for 100LL is extremely difficult.
An entirely new replacement fuel is required to support the existing fleet.
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Engine & Airframe Impacts
A major point of concern for pilots and owners:
Will there be operational or material impacts to my engine or airframe?
What I Won’t Cover
science
Detonation Testing & Potential Hardware Changes/Modifications
Please attend the respective presentations or seek data regarding fuel performance and potential impacts to your specific aircraft and engine from these sources:
Avgas Timeline
1970–1996
Auto Lead Phase-Out
US Clean Air Act bans leaded auto gas. Aviation is exempted due to a lack of safe high-octane alternatives.
1971
100LL Standardized
ASTM D910 introduces 100LL as a lower-lead fuel. It remains the dominant fleet fuel for 50+ years.
2014
PAFI Established
FAA launches the Piston Aviation Fuels Initiative to standardize testing for candidate unleaded formulations. Multiple fuel candidates attempted to replace 100LL
2022
EPA Endangerment Study Begins
EPA issues its proposed finding that leaded avgas emissions pose a public health danger, starting the regulatory clock.
Sept 2022
G100UL Fleet STC
GAMI secures FAA approved Supplemental Type Certificates (STCs) for G100UL, covering the entire US piston fleet.
Oct 2023
EPA Endangerment Finding
EPA finalizes its health danger finding, legally mandating the FAA and EPA to coordinate a leaded fuel phase-out.
2022–Present
EAGLE 2030 Goal
The EAGLE coalition commits to a target date of 2030 to completely eliminate leaded avgas in US civil aviation.
2026
Unleaded Fuels
Three candidate fuels vying for 100LL replacement at different levels of maturity
FAA - Piston Aviation Fuels Initiative (PAFI) Program
2014 - Program Launch
Initiated to evaluate and identify candidate unleaded fuels to create a viable, seamless ‘drop-in’ fleet wide replacement for 100LL
2016 - Candidate Narrowing
Highly structured evaluation process successfully narrowed down 17 initial candidate fuels to just 2 for final phase testing
2018-2019 - Fuel Testing Suspended
Operational and materials compatibility issues identified in 2 candidate fuels
Program Documentation
One Thing That Has Been Learned…
100LL Fuel Specs & Challenge of ‘Drop-in’
Governed by ASTM D910 & Key Requirements
thermostat
Volatility
Reliable cold engine starts
Preventing vapor lock
How does fuel evaporate? (distillation curve)
whatshot
Combustion
Motor Octane Number (MON)
99.6
Rich Octane Number (RON) 130.0
Net Heat of Combustion 43.5 MJ/kg
science
Composition
Chemical hydrocarbon makeup
Allowable additives
No deposits,etc
security
Stability & Safety
Storage
Non-corrosive
Materials compatibility
KEY TAKEAWAY
Removing metals (Lead) from fuel and replacing with other octane enhancers may lead to material compatibility issues with the fuel
National Academies of Sciences
Pathways for New Fuel Approval
Comparing Fleet Authorization and AML STC for new aviation gasoline.
Two Approval Paths
The FAA provides two distinct regulatory mechanisms to authorize unleaded fuels for fleet-wide use.
1. Fleet Authorization
An industry-wide collaborative process (e.g., PAFI) establishing broad, government-supported certification.
2. AML STC
Approved Model List Supplemental Type Certificate pursued by individual applicants or specific OEMs.
Please see Eagle’s website and presentations for more information. www.flyeagle.org
Option 1
Option 2
PAFI
STC
Visualization of Pathways
Fleet Authorization - Policy Statement
PS-AIR-600-20-01
Fleet Authorization Process
Document outlines the process for fleet authorization, including any potential modifications.
“The FAA will then issue an SAIB to identify the qualified fuel, specify the aircraft and engines eligible to use the qualified fuel, and provide references and other information to accomplish the alteration necessary to enable the use of the fuel.”
California 2021-Present UL94 Experience
STC pathway can yield successful results
The RHV Context
Without 100LL for three years, users at Reid-Hillview (RHV) could use Swift’s UL94 or had to travel to other airports to fuel up with 100LL.
public
>5,800,000 Gallons
Sold worldwide to date
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No Issues in California
Zero issues reported locally in California.
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UND Valve Recession
University of North Dakota reported valve recession in specific testing scenarios.
science
Peak EGT
Peak Exhaust Gas Temperature operation used at UND, per POH
Back to the story…
Nov 2024 - G100UL Arrives @ RHV
local_airport
Onsite Fuel Availability
Owners of aircraft requiring 100 octane avgas welcomed having G100UL fuel onsite at Reid-Hillview Airport (RHV).
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Seamless Transition
Stated and marketed as a direct, seamless 'drop-in' replacement for standard 100LL avgas.
Issues Reported
Multiple aircraft in the area started reporting issues within a month
local_airport
Users Report Adverse Effects
Examples below highlight common themes (more examples exist)
Experimental Amateur Built 2007 RV-6
Materials Were Already A Topic of Discussion
June 2024
Cirrus Advisory
Official service advisory raised material compatibility concerns regarding G100UL use.
July 2024
AOPA Baron
Reports of wing staining and paint degradation surfaced during Airventure 2024.
July 2024
Developer Warning
A prominent fuel developer stated that a seamless, true drop-in replacement is not possible.
Center for Environmental Health Lawsuit
Dec 2024
Attempt to prematurely ban 100LL in California
Attempt to amend a settlement decree about signage and now threatens to prematurely ban 100LL in California and replace with G100UL
Case Media
Environmental Group Asks Court To Enforce Consent Agreement
Can I put this in my aircraft?
Engine not on AML STC for G100UL & I had materials compatibility concerns
Pponk/Northpoint O-470-50
My 182’s engine is an STC’d engine with a modified data plate which is not on the AML for G100UL
•Requires 100/130 aviation gasoline
•Engine made up of Continental 470 and 520 components
•Requires a field approval for installation
I have asked the FAA for a clarification on this topic
Meanwhile, In Response to Paint Issues
DECEMBER 14, 2024
The Head of Engineering for GAMI posted an statement on the Mooneyspace forum regarding material compatibility:
KEY STATEMENT:
“7) - G100UL Avgas is NOT a threat to normal aircraft paint.”
Source Forum Thread:
FAQ says it does not cause paint damage
I started researching…
The FAA published three documents covering fuel development and testing in the PAFI program from 2014 through 2022:
Highlights that materials compatibility, engine durability, detonation performance, and deviations from existing ASTM standards are the most critical factors for new fuel acceptance and fleet-wide safety
Detonation testing on critical engine models, establishing "worst-case" test fuel formulations, assessing engine performance vs. fuel density, and mitigating property-driven operational issues like durability, cylinder deposits, and propeller vibration
Fuel properties—such as density, distillation, and material compatibility—along with comprehensive full-scale engine and aircraft testing protocols
Materials Compatibility
Because the STC process is proprietary between the FAA and STC holder, a list of tested materials, components, and aircraft during certification may not be published by the STC holder.
GAMI Update - August 2025
GAMI has since published a material test summary
FAA PAFI Program Resources
The FAA PAFI program has posted their test plan and matrix:
PAFI-MTP-002 Rev B
Public Release Test Plan
FAA Piston Aviation Fuels Initiative
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Key Takeaway
Critical Testing Criteria
Material Compatibility is one of the critical criteria, overshadowing detonation as the key differentiator for acceptability of PAFI fuels.
PAFI Lessons Learned Report
Source Document: PAFI_Fuel_Development_Testing_Lessons_Learned.pdf
FAA PAFI Lessons Learned
Aromatic Content Impact
“Low boiling point aromatics, which are common constituents of aviation gasolines, are known to affect elastomers to a greater extent than other components in aviation gasoline”
Examples:
Cessna 421 Owner - Paint & Yellow Staining
Source Document: PAFI Lessons Learned
Seems awfully similar to Lessons Learned photo?
DECEMBER 15, 2024
Fuel Acquisition
Acquired a gallon of G100UL for testing
FUEL SAMPLES
Personal Testing
Began some materials testing on personal aircraft parts in my garage
“Ok, I gotta see this for myself...”
Especially if 100LL might be banned in California pretty soon!
Initial Personal Materials Testing Started (Dec 2024)
Aircraft Painted Panels
Tested painted panels off of my own aircraft. Noted significant paint deterioration after limited duration exposure.
O-Ring Expansion
Tested various O-rings and observed that nitrile swelled significantly, while increasing force to move an engine primer
EZ Turn Lubricant
Degradation of EZ Turn Lubricant after exposure to fuel
A36 Bonanza @ E16
Advocate of Unleaded Fuels
Burned 531 gallons or ~7% of G100UL sold at RHV & WVI as of Mar 7, 2025.
Paint Degradation
Significant degradation and bubbling observed on the aircraft fuselage surfaces
Yellow Staining
Pronounced yellow discoloration and staining on the cockpit inlet vent near the wing roots
Breather Deposits + Clogged Injector
Deposits and varnish accumulation near the breather exit on the oil filler cap.
Owner had a clogged injector over Mexico
Dipstick Varnish
Heavy varnish and foreign matter detected directly on the oil dipstick where the breather exits
Initial Tests Led to a Series of Ten Videos
Comparative Testing of 4 avgas fuels
I do not have time to cover all the results in detail today, but will summarize in following slides
Fuels I’ve tested
Left to Right
UL94 (not shown) only had a subset of testing and won’t be covered. No issues noted.
G100UL
UL100E
100LL
100R
Octane Enhancer(s)
G100UL
Xylene
Aromatic Amines
UL100E
ETBE
100R
ETBE
100LL
Toluene
Lead (TEL)
Paint Testing
Paint Testing
Exposed various painted panels to fuels to mimic what was happening in the field (leaks)
100LL - No issues observed
100R - No issues observed
G100UL - High Risk of severe
peeling & staining
UL100E - No issues observed
O Rings
Submersion in fuels to evaluate swelling or deterioration effects
Numbers below are volume change (%)
Nitrile (MS29513-014)
100LL - 4-15%
100R - 6%
G100UL - 36%
UL100E - 6%
Fluorosilicone (MS29588/1-338)
100LL - 15%
100R - 21%
G100UL - 21%
UL100E - 15%
Cork-Nitrile Gaskets
Exposed cork-nitrile gaskets to four fuels to evaluate effects
Dimensional swell varied by fuel type
100LL - Minor swelling (<5%)
100R - Minor swelling (<5%)
G100UL - Severe swelling (~18%)
UL100E - Minor swelling (<5%)
EZ Turn Lubricant
Aka ‘Fuel Lube’
Performed testing based on PAFI test plan
100LL - No deterioration identified
100R - No deterioration identified
G100UL - Cracking and separation of grease, plus discoloration
UL100E - No deterioration identified
UL100E
MIL-6000 Hoses
MIL-6000 ¾” ID Hose
Deterioration
100LL - No deterioration identified
100R - No deterioration identified
G100UL - No deterioration identified
UL100E - No deterioration identified
Swelling
100LL - Minor effects
100R - Minor effects
G100UL - Minor/Medium effects
UL100E - Minor effects
Permeation
100LL - Minor
100R - Minor
G100UL - Severe
UL100E - Minor
Tubing - Fuel Sight Gauges
Simulated a cockpit fuel sight gauge
Versilon C-210-A (left)
100LL - No issues identified
100R - No issues identified
G100UL - Stained and permeated
UL100E - No issues identified
Tygon F-4040-A (right)
100LL - No issues identified
100R - No issues identified
G100UL - Stained and permeated
UL100E - No issues identified
Fabric
Exposed two fabric samples to four fuels to evaluate effects
100LL - Staining from dye
100R - Staining from dye
G100UL - Degradation of fabric cement and separation of silver layer from fabric
UL100E - Staining from dye
Bladders
Seven different bladder materials were exposed to four different fuels
Evaluated for degradation of material, leakage, and permeation
BTC-85 Goodyear/Meggit
Bladder Permeation Rates
Note: These were optimized for 100LL
Bladder Cavity Tape
Tested permeation of 4 bladder materials to see if constituents would degrade cavity tape in a wing
100LL - One slight softening
100R - None identified
G100UL - 3 of 4 bladder materials allowed degradation of tape adhesive
UL100E - None identified
Polysulfide Sealant
Exposed three fuels to Polysulfide sealant - CS3204 B2
Exposure duration: <1 month
100LL - No issues identified
100R - No issues identified
G100UL - Softening (flexible), durometer decrease & possible loss of adhesion to aluminum
UL100E - No issues identified
Polysulfide Sealant
Exposed three fuels to Polysulfide sealant - CS3204 B2
100R - No issues identified
G100UL - Softening (flexible), durometer decrease & apparent loss of adhesion
UL100E - No issues identified
Pull test of bonded sample to 5 ft-lb showed more pliability and flex in material with G100UL
Summary Table
Other Interesting Findings - Plastics
Bonanza Owner
Other Interesting Findings - Color
Some fuel constituents darken in exposure to air and light
G100UL
100LL/G100UL mix
Stored in cabinet
G100UL
Darkened
100LL/G100UL mix exposed to light
Dec 2024
April 2025
G100UL
Right out of pump
So, Where are we Currently in the Unleaded Transition?
GAMI - G100UL
Received STC in 2022
RHV (Nov 2024)
• Current sales are slow (~150 gal/month)
WVI (Nov 2024)
• Reverted tank to 100LL in June 2026
Tupelo, MS
• Unknown sales volume
Refugio, TX
• Will sell you 55 gallon drum
VP/Lyondell - UL100E
PAFI Program
Currently going through the rigorous testing of the formal PAFI program framework.
ASTM Specification
Expecting final testing in 2026
Swift - 100R + UL94
UL94 Success
Has had great success overall across the target fleet. >2,000,000 gallons sold in California
100R Development
STC certification actively progressing.
ASTM Specification
Recently expanded STC AML
Considerations For Owners
Consult Official Sources
Trust But Verify
Report Issues
FAA Special Airworthiness Bulletin (SAIB)
Seeking Operator Input
The FAA is actively gathering information regarding user experiences with all types of unleaded fuels to ensure safety and operational standards.
SAIB 2025-04
“This Special Airworthiness Information Bulletin (SAIB) advises aircraft operators, fixed base operators, FAA repair stations, FSDOs, and Foreign Civil Aviation Authorities to report to the FAA any issues (service difficulties, maintenance) related to the use of unleaded fuel when used as an alternative to any other fuels.”
Industry OEMs
The major aircraft manufacturers and OEMs have issued clear, formal statements regarding approved fuels.
Common theme from manufacturers
Materials Compatibility
Concern for information on fuels & testing
Ceramic Coatings (Composite Aircraft)
warning Warranty Warning
Aircraft under warranty that choose to be modified by STC for G100UL and use the fuel will likely void their warranties.
Cirrus Aircraft
Textron / Cessna
Piper Aircraft
Lycoming Engines
Follow Manufacturer Guidelines
Always refer to official service instructions and bulletins to ensure compliance and maintain engine warranties.
LYCOMING BULLETIN ON ADDITIVES
“WHEN USING THE UNLEADED FUELS IDENTIFIED IN TABLE 1, LYCOMING OIL ADDITIVE P/N LW-16702, OR AN EQUIVALENT FINISHED PRODUCT SUCH AS AEROSHELL 15W-50, MUST BE USED.”
— Service Instruction No. 1070AB
Want to Review this in More Detail?
AirVenture presentation will be posted on this site (QR code next slide)
Questions?
https://sites.google.com/view/unleaded-avgas