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

At winter-contaminated movement areas, the interfacial materials—snow and ice—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 rapidly and so a frequent reporting service of the surface conditions is warranted. Friction is both material and system dependent. An ongoing Joint Winter Runway Friction Measurement Program (JWRFMP) addresses this issue in an international effort to produce reliable data on friction at winter-contaminated movement areas in potentially slippery conditions. The traditional approach has been to measure the friction with tribometers to generate μ, the “friction number”. The substantial question is: what are these friction numbers? JWRFMP encourage a broad multidisciplinary approach to solve this question and to provide the international aviation industry with the best information attainable. The goal is to provide an International Runway Friction Index (IRFI) that comprises the relevant information to be used for the pilot/aircraft system. This IRFI should be based upon sound basic physics and an analytic approach to understanding and to solving the tribological problems involved. In this paper the interaction of aircraft wheel(s) on travelled winter surfaces of a movement area is outlined by a tribosystem and the operational envelope for the system is described.