This Data Item will present an empirical model that defines the decelerating forces acting on aircraft tyres when rolling or braking on surfaces typical of those used for runways and taxiways. The model is valid for uncontaminated surfaces and for those contaminated by water@ slush@ snow and ice. In order to calculate decelerating forces@ in addition to an approximation to the operating slip ratio for an aircraft's braking system@ it is necessary to know values of only eight variables@ all of which are used in customary calculations of aircraft performance. In the particular case of winter precipitation@ the model includes the statistical variation of the mechanical properties of snows and frictional characteristics for surfaces that are completely covered with ice or compressed snow. All these statistical variations are identified from experiments on aircraft and ground vehicles. Through the mechanism of a reference coefficient of friction@ the model can also be used to link the performance of aircraft and ground vehicles. The modelling covers a range of the independent variables sufficient to establish Flight Manual data for any type of aircraft.