From NASA: ASRS Newsletter Re: Unleaded Fuel

[GAHorn]

This FBO repair facility Aviation Maintenance Technician reported a serious safety issue. The investigation and level of concern clearly indicate superior professional dedication to the safety of flight and aviation itself.

AMENDED: The mission of ASRS is to de-identify and disseminate safety reports to the proper authorities who can investigate and determine if an action is warranted. In this case, after publication of the December 2024 CALLBACK, the fuel producer contacted us stating that they disagreed with the accuracy of the report and believed the fuel used by the reporter was not UL94. They stated that "UL94 has the same hydrocarbon chemistry as 100LL (absent tetraethyllead) and accordingly ASTM results show the fuel does not react to cadmium plated metals. ASTM requires every batch of UL94 to report a (more prone to react) copper strip corrosion test result - confirming there is no adverse reaction of UL94 to metals."

■ Increased frequency of maintenance [is] required on carburetors and fuel injector systems due to suspected cadmium particulate matter being found in float bowls, fuel injector nozzles, fuel screens, and fuel jets. This impacts fuel flow and metering, impacting engine performance due to restriction of fuel flow. This phenomenon was observed on aircraft during unscheduled maintenance due to complaints of loss of power and also during routine scheduled maintenance. Particulate accumulation [was] also found in check valves, auxiliary fuel pumps and mechanical engine pumps. Clumps and screen obstruction [were] observed. This has been observed over the past four months, since aircraft started using Unleaded 94 Octane (UL94). The exact source of the cadmium is not definitively determined at this time. We suspect the cadmium is held in suspension in the fuel, and in addition to accumulating and clogging the fuel system, some particles are entering the combustion chamber with unknown impacts on cylinders, valves, and exhaust systems. A simple experiment was conducted. Aviation cadmium bolts were placed in [100 Octane Low Lead] 100LL and UL94 for a few hours. The bolts in 100LL remained intact with no change. The bolts in UL94 showed flaking with particles suspended in the fuel, sparkling. Cleaning of all fuel parts in the fuel systems clears the problem, but it reappears. We are concerned since we have limited experience with UL94 and have not seen anything like this in our careers, which total over 50 years together as A&P and IA [Inspection Authority Mechanics].