Effects of the structure and properties of ice and snow on the friction ofaircraft tyres on movement area surfaces

At winter-contaminated movement areas, the interfacial materials-snow and i ce-cause the major operational problem related to aircraft performance. The central issue is how to evaluate the attainable friction force between the aircraft tyre(s) and the pavement and relate that to aircraft performance. In wintertime the operational window for aircraft movements can change rap idly and so a frequent reporting service of the surface conditions is warra nted. Friction is both material and system dependent. An ongoing Joint Wint er Runway Friction Measurement Program (JWRFMP) addresses this issue in an international effort to produce reliable data on friction at winter-contami nated movement areas in potentially slippery conditions. The traditional ap proach has been to measure the friction with tribometers to generate mu, th e "friction number". The substantial question is: what are these friction n umbers? JWRFMP encourage a broad multidisciplinary approach to solve this q uestion and to provide the international aviation industry with the best in formation attainable. The goal is to provide an International Runway Fricti on Index (IRFI) that comprises the relevant information to be used for the pilot/aircraft system. This IRFI should be based upon sound basic physics a nd an analytic approach to understanding and to solving the tribological pr oblems involved. In this paper the interaction of aircraft wheel(s) on trav elled winter surfaces of a movement area is outlined by a tribosystem. and the operational envelope for the system is described. (C) 2001 Published by Elsevier Science Ltd.