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Jet-A and 100LL have an interesting relationship. They are both literally the fuel that powers aviation and, at the same time, are completely incompatible. An NTSB report on a misfueled Cessna 421C (N28RH) serves as a reminder of why simple assumptions by both pilot and fueler can quickly lead to catastrophic consequences. The events unfolded when the Cessna 421's pilot refueled at an airport in Blytheville, Arkansas on August 21 and subsequently departed, bound for Lima, Ohio. According to the NTSB report, the No. 1 cylinder on the right engine was running hot during climb-out, so the pilot chose to feather the propeller and shut down the engine. He tried to divert to Fulton Airport (1M7) in Kentucky, when the left engine's performance began to deteriorate. The pilot could not maintain altitude and performed a forced landing in a cornfield two miles from the airport. The aircraft sustained substantial damage to the right engine mount, fuselage, and empennage as a result. Two occupants on the aircraft were seriously injured, while the other two had minor injuries. A first responder on the scene reported that the fuel in the Cessna's tanks had no color and smelled like diesel. Reportedly, when the pilot had refueled at the airport, he had only requested a "top off" and did not specify that he needed 100LL fuel. The fueler assumed the airplane needed Jet-A because avgas customers at the airport typically use a nearby self-service pump. The fueler loaded about 70 gallons in one tank and 75 in the other, 145 gallons of Jet-A in all. A fuel receipt signed by the pilot showed the Jet-A. The pilot told investigators he read the receipt and saw that Jet-A had been supplied, but the group wanted to get home and left without inspecting or sampling the fuel. The airport now uses a form for pilots to specify both the type and quantity of fuel they want. The airport manager told investigators the fueler no longer works there. The NTSB determined the probable cause was the misfueling by the refueler, with the pilot's failure to verify the airplane had been properly fueled before departure as a contributing factor. The fueling mistake could have been avoided at multiple points, including the fueling process itself, review of the fuel receipt, and the pilot's preflight verification procedures. Those missed checks are ultimately what turned a fueling error into an accident. The fixes are procedural: confirm quantity and fuel type out loud and treat the receipt as a final check. While the airport's fuel request form will not eliminate human error entirely, those procedural barriers are more effective than relying on trust or assumptions alone. What refuelers and operators should remember Fuel type should never depend on a process that was simply repeated from the last time it was performed. 100LL is dyed blue, and the fuel in this airplane was colorless. A sump sample before engine start would have shown the difference, and that check stays with the pilot no matter who fueled the airplane.