Because of ram-air heating of the wings. Forward motion of the airplane keeps the wings heated sufficiently to keep fuel temperatures just above freezing. (However, once the fuel flows down into the pipes on its way to the engines, it will start freezing, unless the path is very short.)

Although the outside air temperature at a typical cruising altitude of 35,000 feet can drop below -50°C (-58°F), airplanes do not "freeze" because they are equipped with sophisticated anti-icing and de-icing systems. The most common method used in 2026 for commercial jets is the Thermal Anti-Ice (TAI) system, which "bleeds" hot air from the jet engines and pipes it through the leading edges of the wings and the engine inlets. This intense heat prevents ice from ever forming on these critical surfaces. For smaller or propeller-driven planes, "pneumatic boots"—rubber membranes on the wings—can be inflated and deflated to physically crack and shed any ice that accumulates. Additionally, critical sensors like Pitot tubes are internally heated with electricity to ensure they don't clog. Interestingly, the high speed of the aircraft also helps; the friction between the air and the plane's skin (aerodynamic heating) can raise the surface temperature slightly above the ambient air temperature, providing a small natural defense against ice crystals, though the mechanical heating systems remain the primary safety barrier.