Aviation fuel is a mixture of different hydrocarbons. The longer the hydrocarbons are and the higher the molecular weight of the compounds, the more the chemical parameters such as melting point or smoke point differ. These chemical parameters have a considerable influence on the quality of the aviation fuel. An important parameter for quality control used by aviation fuel manufacturers is the viscosity.
The purity of the aviation fuel in particular is of vital importance: If the fuel is contaminated with water, ice may form in the fuel tanks and fuel lines at high flying altitudes – a dangerous situation. These ice crystals would disturb or interrupt the flow of fuel to the turbines. At worst this could lead to a failure of the turbines during the flight.