## 4 International Runway Skid Resistance Standards and Regulations
### Micro and Macro Surface Texture  
To maintain proper skid resistance, ICAO also recommends providing a good texture depth and performing rubber contamination removal and/or resurfacing as required [75]. The mean texture depth (MTD) of the runway surface should be more than 1 mm [7]. Proper texture enhances the contact between tire and pavement and increases the draining capability of the surface-tire contact area [7] and ICAO also recommends using surface materials with good texture, such as stone mastic asphalt, porous and open graded asphalt concrete. Alternatively, a surface treatment, such as grooving, is a recommended alternate [76].  
ICAO also recommends providing good microtexture. However, there are no test methods for assessing the microtexture and microtexture limits are not specified. Rather, Doc 9981 [66] contains recommendations for microtexture assessment by touch and by visual assessment to detect excessive rubber contamination [66]. However, this is unreliable and is not recommended. Where microtexture is low, shot blasting can be used to increase the microtexture and to clean rubber contamination [68]. Ultra-high-pressure water blasting and chemical treatments are also available, with water treatments most common because they avoid the shots that can damage the aircraft if left on the surface, as well as the chemical treatments that can adversely impact the environment [77; 78; 79].  
For macrotexture measurements, volumetric and profilometry methods are recommended [7]. The volumetric method evaluates the MTD value, while the profilometry method evaluates the mean profile depth (MPD) [80]. ICAO allows the use of both meth  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Runway** & & **Pilot Report of** & \\
**Condition Code** & **Runway Condition Description** & **Runway Braking** & **Description of a Braking Action** \\
**(RWYCC)** & & **Action** & \\ \hline
6 & Dry & N/A & N/A \\  & Frost. & & \\  & Wet (\(\leq\)3 mm) & & Braking deceleration is normal for \\
5 & Slush (\(\leq\)3 mm) & & the wheel braking effort applied \\  & Dry snow (\(\leq\)3 mm) & & and directional control is normal \\  & Wet snow (\(\leq\)3 mm) & & \\
4 & Compacted snow (outside air & & \\  & temperature below \(-\)15 \({}^{\circ}\)C) & Good to medium & \\  & Wet (slippery then wet due to poor & & \\  & micro or macrotexture) & & \\  & Dry snow (\(>\)3 mm) & & \\
3 & Wet snow on top of compacted snow & & \\  & Wet snow on top of compacted snow & & \\  & Wet snow on top of compacted snow & & \\  & Compacted snow (outside air & & \\  & temperature above \(-\)15 \({}^{\circ}\)C) & & \\
2 & Standing water (\(>\)3 mm) & & \\  & Slush (\(>\)3 mm) & & \\  & & & \\  & & & \\
1 & Ice & Poor & \\  & & & \\  & Wet ice & & \\
0 & Water on top of compacted snow & Less than poor & \\  & Dry or wet snow on top of ice & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Runway condition code assessment and braking performance of an airplane [66].  
ods; however, volumetric methods, such as the grease smear and sand path methods, are preferred. Annex 14 [7] states that in the case of profile measuring techniques, a conversion between MPD and MTD must be established for the measuring equipment used [7]. At the same time, Circular 355 states that there is no universally agreed relationship between MTD and MPD [68].