After calculating the friction coefficient for an asphalt runway pavement through a test, how to know if it’s acceptable or not? In other words, hat is the lowest acceptable value for friction coefficient specified by ICAO or other related organizations?
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$\begingroup$ Do you mean for dry pavement? Or the lowest that aircraft can operate on? $\endgroup$– Ralph J ♦Jul 20, 2021 at 23:34
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$\begingroup$ The lowest acceptable for dry pavement $\endgroup$– AeroEngJul 21, 2021 at 6:54
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$\begingroup$ Depends on speed. $\endgroup$– Peter KämpfJul 21, 2021 at 16:05
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1 Answer
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ICAO
In Doc 9137, Airport Services Manual - Part II Pavement Surface Conditions, ICAO requires 3 levels of friction to be defined at local AIP level.
3.2.11 States should specify three friction levels as follows:
a) a design level which establishes the minimum friction level for a newly constructed or resurfaced runway surface;
b) a maintenance friction level below which corrective maintenance action should be considered; and
c) a minimum friction level below which the information that a runway may be slippery when wet should be made available and corrective action initiated.
They also provide a sample table:
which is based on experience with different friction-measuring devices, shows the criteria in use in some States for specifying the friction characteristics of new or resurfaced runway surfaces, for establishing maintenance planning levels and for setting minimum friction levels.
Actual values for the US are therefore defined by FAA:
FAA
In AC 150/5320-12C, levels are defined according to the measurement method, with the three levels recommended by ICAO. At first sight there is no difference with ICAO sample table.
TABLE 3-2. FRICTION LEVEL CLASSIFICATION FOR RUNWAY PAVEMENT SURFACES
UK CAA
A similar table is found in CAP 683:
EASA
Apparently there is no EASA equivalent, each State member of EASA seems to have it own method. For more information, see this study to try move forward, without apparent further actions.
On the other hand the friction matter is a complex one, and measuring the state of the runway under some conditions does not give all the information required to evaluate, say the length required in case of RTO or for braking in rainy weather.
Related: How are runway conditions measured?
