On January 24, 2025, members of the Black Forest Soaring Society (BFSS) conducted what are believed to be the first glider aerotows in Colorado using a tow plane powered by unleaded UL94 aviation gasoline (avgas). The historic flights took place at Kelly Airpark, a privately owned airfield near Elbert, Colorado, built exclusively for resident aviators. BFSS is testing the use of UL94 after their long-time fuel supplier announced last year that it would no longer provide 100 low lead (100LL) aviation fuel.
In preparation for these flights, BFSS chief tow pilot Bill Gerblick obtained the necessary FAA supplemental type certificate to operate the club’s Piper Pawnee tow plane on unleaded avgas. He then flew the aircraft to Centennial Airport (KAPA) in Denver, where he filled its tanks with UL94 fuel purchased from the Denver Jet Center. That single tank of unleaded fuel was sufficient to complete a full day of scheduled glider tows, launching two BFSS two-seat gliders and several club pilots to altitudes ranging from 8,000 to 11,000 feet above mean sea level (MSL).
 A noteworthy aspect in the day’s operations came when Kip McClain, Aviation Planner for the Colorado Division of Aeronautics, piloted the L-23 glider for the club’s first UL94-powered aerotow. An avid glider pilot and ten-year BFSS member with two decades of soaring experience, Kip had planned a recurrency training flight with longtime BFSS instructor Stan Bissell. Scheduled weeks in advance, the flight unexpectedly aligned with this milestone event. Under Stan’s mentorship, Kip completed two flights, reporting that “no problems were encountered during the 500-foot-per-minute climb to 11,000 feet MSL in glass-smooth air.”
Inset Photo: Aeronautics Division Planner Kip McClain (front seat) and Stan Bissel immediately prior to launch in the L-23 sailplane. Photo, Kip McClain.
Towing operations continued smoothly throughout the day, with Bill Gerblick and fellow tow pilot Doug Houston launching gliders into the crisp and calm blue skies over Kelly Airpark without a single glitch. As Mark Palmer, editor of the BFSS Airworthy newsletter, noted: “Bill and Doug conducted several tows and reported they could tell no difference in performance between UL94 and 100LL. While it’s only one day of use, it’s a positive result.” He added, “The real test will come as we move into warmer weather—how UL94 performs in high temperatures, at high-density altitudes, and with heavier gliders remains to be seen.”
Beyond marking a historic step in aviation fuel transition, the successful use of UL94 introduced a new possibility for fueling operations at Kelly Airpark. BFSS is currently in discussions with a UL94 supplier, and if everything aligns well, unleaded avgas could soon become the standard for pilots flying there. BFSS owns property on-site and has traditionally facilitated 100LL deliveries for itself and other aviator residents. This shift could pave the way for broader adoption of unleaded aviation fuel at the airfield. |
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