Techniques and Methods for Runway Friction Measurement: A Review of State of the Art

Accidents in which aircrafts veered off the runway when landing have occurred frequently, which pose a considerable threat to people's lives and property. Friction, produced by the contact patch between the tires and the runway, has long been known as a crucial factor for a safe landing. Therefore, accurately measuring the friction coefficient (F-Coe) is regarded as an effective means to reduce accidents, especially in extreme weather. This review article aims to summarize and analyze the state-of-the-art techniques of runway friction characteristics measurement to provide all stakeholders a broader understanding and more valuable references. First, the methods available for measuring (or estimating) the friction characteristics are reviewed, such as American Society of Testing Materials (ASTM) standard test, the caused-based method, the effect-based method, modeling method, and fusion method. Second, the pros and cons of these methods are discussed from two aspects: conventional method and the tribo-system-based method. Third, the research progress of the correlation between the F-Coe obtained by ground measurement equipment and the aircraft braking F-Coe (ABF-Coe) is summarized and discussed. Finally, the measurement policies, about runway surface friction characteristics, proposed by International Civil Aviation Organization (ICAO), Federal Aviation Administration (FAA), and European Aviation Safety Agency (EASA) in recent years are summarized and the measurement methods are proposed or improved according to these policies. For developing better and proper measurement methods of runway F-Coe (RF-Coe), the future envisaged research lines should focus on the new measurement techniques and methods under the joint action of tires, runway, contaminants, and atmospheric condition.