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Author Background

Nick Wilson is an Associate Professor of Aviation at the University of North Dakota. Nick holds an MBA and PhD and researches human factors and performance as well as topics in aviation sustainability. Nick is an active pilot and flight instructor.

Ryan Guthridge is an Associate Professor Aviation at the University of North Dakota. Ryan holds an MBA and PhD and researches topics related to flight data analytics, safety, and aviation sustainability. Ryan is an active pilot and flight instructor.

Brandon Wild is an Associate Professor Aviation at the University of North Dakota. Brandon holds an MBA and PhD and researches topics related to flight data analytics, safety, and aviation sustainability.

Jeremy Roesler holds an MBA from the University of North Dakota and serves as the Director of Flight Operations at UND. Jeremy is an active pilot and flight instructor.

Dan Kasowski is is the Director of Maintenance at UND Flight Operations and holds an FAA A&P / IA. Dan is a 2024 inductee into the North Dakota Aviation Hall of Fame.

Nick Geinert is the Accessory Shop Manager for UND Flight Operations Maintenance and holds an B.S. Aviation Technology Management as well as an FAA A&P / IA.

Aaron Terbest is an Flight Data Analyst with UND Flight Operations Safety. Aaron holds a B.S. in Commercial Aviation from the University of North Dakota. Aaron is an active pilot and flight instructor.

Aaron Fettig is an Aviation Safety Specialist with UND Flight Operations Safety. Aaron holds a B.S. in Commercial Aviation from the University of North Dakota. Aaron is an active pilot and flight instructor.

Robert Kraus is the Dean of the John D. Odegard School of Aerospace Sciences at the University of North Dakota. Dr. Kraus is a retired USAF Colonel with over 3,300 hours of flight time in 35 aircraft types. Dr. Kraus is holds a PhD in Aerospace Engineering from Virginia Polytechnic Institute and State University.

Abstract

The University of North Dakota (UND) adopted unleaded aviation fuel (UL94) for approximately a four-month period in the summer and early fall of 2023. The UL94 fuel was used in all reciprocating engine fleets based at the university’s primary training airport, Grand Forks International Airport in North Dakota. During the operational implementation of UL94, the UND flew 46,600 flight hours, consuming 386,778 gallons of fuel across all fleets powered by Lycoming engines. After approximately two months of using UL94, operational reports and maintenance inspections began to indicate potential for exhaust valve seat recession (EVSR), although early indications were limited in number and could not be attributed to one specific causal relationship. After additional reports and inspections suggested a potential for a larger trend in EVSR and upon recommendation by both Lycoming and Swift Fuels, the university elected to switch back to 100 octane low-lead aviation fuel (100LL) on October 26, 2023. Post hoc analysis of engine exhaust valve tappet clearance measurements (an indication of EVSR) showed a statistically significant negative correlation to hours of UL94 usage (r = –0.52**, p < .001), suggesting EVSR developing with consumption of UL94. Additional analysis of time since overhaul, percent mix of 100LL, aircraft type, and several other metrics were performed as a part of this study. It should be noted that this publication and the UND’s decision to switch to UL94 or back to 100LL were not funded by any private or government organization and should be considered an operational case study in adoption of unleaded aviation fuel.

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