wide-cut
Composed of a mixture of hydrocarbons with a wide range of boiling points, including both moderately-heavy, higher-boiling kerosene-type molecules and lighter, lower-boiling, more-volatile gasoline-type molecules; Jet B or JP-4 is a fuel of this type.
wide-cut: jet fuel that spans light and heavy hydrocarbons
A wide-cut fuel is a refined petroleum product engineered to contain hydrocarbons across a broad spectrum of boiling points, rather than the narrower range you find in conventional jet fuels. The mix typically runs from C8 through C16 carbon chains, pulling in both volatile gasoline-range molecules (boiling around 40-200°C) and heavier kerosene-range molecules (200-300°C). This blending strategy gives the fuel distinct operational advantages in certain climates and aircraft applications.
The classic wide-cut jet fuel is JP-4, which combines the lighter fraction that improves cold-weather handling with heavier components that boost energy density. Jet B, used primarily in northern climates, follows the same principle. The flashpoint of wide-cut fuels typically sits lower than conventional Jet A-1 (around 10-20°C versus 38°C), making them more flammable on the ground but more reliable in extreme cold where conventional fuel can gel or freeze in fuel systems. The Reid Vapor Pressure is correspondingly higher, increasing evaporative losses during storage and flight.
Trade-offs and operational reality
The broader hydrocarbon distribution creates handling challenges that narrower-cut fuels avoid. Wide-cut fuels are more prone to evaporation losses, require sealed storage tanks, and demand stricter attention to fuel system design to prevent vapor lock at altitude. Static electricity dissipation becomes more critical because lighter fractions conduct electricity poorly. For this reason, wide-cut fuels largely fell out of favor for civilian transport aviation after the 1980s, as aircraft designs optimized around Jet A-1 became standard and cold-weather airports improved their handling procedures.
Military and remote-operations aircraft still use wide-cut fuels where the cold-start advantage and lower freeze point outweigh the volatility risk. The term wide-cut refers directly to the separation process: conventional fuels are produced by cutting a narrow band of distillation fractions from crude oil, while wide-cut blends deliberately include a wider cut across the distillation tower. This is not simply mixing two finished fuels; refineries produce it as a distinct product stream by adjusting their fractionation parameters.
Testing wide-cut fuel requires attention to volatility specs that would fail Jet A-1. The ASTM D1655 standard includes separate tables for wide-cut fuels (Jet B, JP-4) that permit higher vapor pressure (25 kPa maximum at 37.8°C, compared to 3 kPa for Jet A-1) and lower flashpoint. Handling personnel need to understand that a wide-cut fuel behaves more like gasoline in a tank than like conventional kerosene jet fuel, and ground equipment, hoses, and seals must be certified accordingly.