Lingering uncertainty associated with measured and estimated runway friction and aircraft braking coefficients can lead to landing distances or maximum landing weights that also are uncertain or inaccurate. “This has contributed to accidents and incidents where aircraft departed runways because the surface was more slippery than expected,” according to the executive summary of a study released in 2011 by the Accident Investigation Board Norway (AIBN).1
In 30 investigated occurrences, the AIBN found that “aircraft braking coefficient (ABC) was not in accordance with the measured/estimated runway friction coefficients (FC).” In its study, the AIBN identified a number of common factors that have reduced safety margins, and factors that explain the differences between ABC and FC. “These factors are related to meteorological conditions and friction measurement uncertainty, runway treatment, operational aspects and regulator…
