The recent news about the University of North Dakota (UND) returning its fleet to leaded fuel after discovering excessive valve recession in aircraft using Swift Fuels UL94 has grabbed the attention of many aircraft operators looking to use lead-free fuel. Excessive valve recession can result in blow-by that can cause an uncommanded loss of engine power, compression, and in worst cases, valve failure.
As reported by FLYING last week, UND resumed the use of 100LL after noting “exhaust valve recession” in the Lycoming engines that power its fleet of Piper PA-28-181 Archers and PA-44-180 Seminoles.
According to UND chief instructor Jeremy Roesler, the school’s 120 aircraft used unleaded fuel between June and October, logging more than 46,000 flight hours. When routine maintenance detected abnormal exhaust valve recession, Roesler said the decision was made to revert back to 100LL as a precaution while the issue was investigated. UND is working with Lycoming and Swift Fuels to address the concern.
“We appreciate feedback from all customers related to the use of fuels in Lycoming engines,” Lycoming told FLYING. “Our team is proactively evaluating the data received from the University of North Dakota Aerospace related to the use of UL94 Fuels, and we will provide appropriate guidance to the industry based on our analysis of this data. Lycoming remains committed to the FAA EAGLE initiative of eliminating lead emissions from piston-engine aircraft by the end of 2030.”
According to Chris D’Acosta, CEO of Swift Fuels, the company became aware of the issue at UND when it was contacted by Lycoming Engines. Immediately, the fuel manufacturer and supplier “went through an audit check.” This means testing fuel from the production facility and all the tanks, both stationary and used in transport, to make sure there was no contamination. None was found, D’Acosta said, adding, “The fuel was on spec.”
The investigation is very thorough, according to D’Acosta, adding that Lycoming is running it and will be “looking at the materials used in the valves, the valve seat, the head of the valve stem, the flight operations telemetry—that’s a fancy way of saying the conditions the flight was operated under.“
Swift Fuels holds an AML-STC FAA approval for UL94 fuel, which each owner-operator can purchase and install on their individual eligible aircraft and engines allowing them to use UL94. Aircraft that require a higher octane, with such higher-performance designs making up approximately 30 percent of the general aviation fleet, are still having to use 100LL.
While UND has the option to revert back to 100LL, other schools are not so lucky. Flight schools at Reid-Hillview Airport (KRHV) in San Jose, California, don’t have that option because the facility is owned by Santa Clara County. In January 2022 the Santa Clara County Board of Supervisors enacted a ban on leaded fuel sales at the county-sponsored airport, located on 180 acres in east San Jose. For several years, politicians in the region have called for the airport’s closure, citing alleged safety issues such as lead poisoning from the use of leaded aviation fuel.
The owners of the flight schools at KRHV saw the ban coming. In 2021, a county-funded study into blood lead levels (BLL) of local children allegedly indicated that the BLL of children who live near the airport is attributed in large part to air pollution from piston-powered aircraft that utilize 100LL. In August 2021 the board of supervisors banned the sale of 100LL in Santa Clara County, effectively removing it from both KRHV and San Martin Airport (E16) south of San Jose.
When the ban went into effect in 2022, the flight schools were already using unleaded fuel, having made the switch to UL94 that summer.
Walt Gyger, the recently retired owner and operator of Trade Winds Aviation, one of the schools at KRHV, was skeptical of the study, noting that it did not take into account lead contamination coming from building materials such as paint and pipes used in the construction of the homes and business in the San Jose area. Many of those were built at a time when the dangers of lead exposure were unknown.
Gyger, who spent 16 years as an FBO owner, said rather than fighting the county on the study results, the flight schools obtained STCs to allow their aircraft to operate on unleaded fuel and made arrangements for Swift Fuels to deliver to the airport.
According to Josh Watson, co-owner of AeroDynamic Aviation at KRHV, the aircraft powered by Lycoming engines were designed to use lower-octane fuel, so putting them on a diet of UL94 was as simple as obtaining the STC and replacarding the aircraft. That was the easy part.
There were logistical challenges transporting fuel from the refinery in Indiana, said Gyger. “The options are by truck or by rail car, which brings it to a terminal and from there to the FBOs,” said Gyger. “A truck can carry eight to 10,000 gallons. A rail car carried 28,000 gallons.”
Unleaded fuel is also more expensive than 100LL, said Gyger, by about $1 per gallon.
“But the flight schools at Reid-Hillview didn’t really have a choice,” said Watson, who in addition to being a pilot holds an A/P/IA certificate. He says his business has also noticed some issues with the valves since the switch to unleaded fuel. The school runs a fleet of 22 aircraft, ranging from Cessna single-engine trainers to Citabrias. It also has a robust maintenance shop and does its maintenance in-house.
“We have to monitor the engine condition very closely,” Watson said. :Around the 1,800-hour range is when the valve issues happen, [and] that’s over the lifespan of the engine. We have noticed some valve recession and some valve deformation and discoloration, and it has made it a little more difficult to run in new cylinders. Typically, the cylinder makes it to TBO (time between overhauls), and we are able to reuse the valve. We can no longer reuse the valve due to valve recession and malformation. When the valve goes out of tolerance, it has to be replaced. We noticed it on a set of brand new cylinders. It is odd for a first run set of cylinders to have a problem like that.”
Other Flight Schools
Gyger recently sold Trade Winds Aviation to American Flight Schools (AFS), which owns several FBOs in California, and ones in Portland, Oregon; Carney, Nebraska; and Centennial, Colorado. All of them are using UL94, according to Danny Smith, chief operating officer for AFS. The fleet is made up of more than 125 aircraft, flying on average 6,000 hours per month. “Centennial, KAPA, is our largest operation,” Smith said.
According to Smith, when AFS made the switch to unleaded fuel in May, it was very cautious about how it would impact aircraft operations.
“At Centennial, especially in the summer, we experience very high density altitude, sometimes more than 9,000 feet,” Smith said. “We were concerned about performance, but we had no reports of degraded performance from pilots or instructors in aircraft burning UL94. They were still reporting 1,000- to 1,200-feet-per-minute climbs on takeoff.”
In addition, Smith said the aircraft are experiencing lower engine temperatures and less deposits on spark plugs. “The engines are burning cleaner,” he said. “We have not had the experience of UND. There have been no valve recessions.”
Smith noted that, although AFS is paying more for a gallon of UL94 than it did for 100LL, “the operating cost of the fuel is reduced by not having to replace six to eight spark plugs every 100 hours. Spark plugs run about $40 to $60 each, so the cost of maintenance has come down because we don’t have to replace spark plugs contaminated by lead.”
In the meantime, Swift Fuels continues development on a replacement fuel for the higher-performance general aviation engines that require a higher octane for safe and efficient operation. According to D’Acosta, “100R, the 100 octane replacement fuel for 100LL, is going through the steps and stages for approval from the FAA,” adding that the FAA and ASTM international have a long list that you must comply with and specific methods that must be used to show compliance.
Swift Fuels is hopeful 100R will be certified by the end of 2024.
“It is challenging,” D’Acosta said. “There is lots of collaboration and diligence, and safety matters. We are working with county governments, FBOs, pilots, technicians, and mechanics. There are lots of dimensions to get it going. We have been working on 100R for three or four years through a variety of channels. We move at the speed of the FAA and the speed industry. Our goal is to be the global leader in unleaded fuels.”
