## 3 Methodology
### Condition Evaluation of Airport Pavement Performance in APMS
As shown in Table 2, the FAA provides recommendations for friction measurement frequencies, and these assessments, combined with visual inspections and routine maintenance, are vital for sustaining pavement performance and ensuring aviation safety [29; 36; 37]. Friction measurements on runways are conducted along the runway centerline and 3 m outward. Values obtained from friction measurement equipment guide the assessment of surface friction deterioration and help determine appropriate corrective actions for safe aircraft operations. Measurements are taken at test speeds of 40 and 60 mph (65 and 95 km/h), with results classified into three levels of friction. Table 3 presents limit values for friction measurements taken by different devices at a test speed of 65 km/h as established by the FAA [37]. Airport pavement performance is assessed through structural strength testing methods, including destructive and non-destructive techniques. Destructive tests involve extracting core samples for laboratory analysis, while non-destructive methods, such as Rayleigh wave testing, are preferred for their non-invasive nature. The ACN/PCN system, developed by the International Civil Aviation Organization (ICAO), is used to determine aircraft weight limitations based on pavement strength, where an aircraft can operate without restrictions if its aircraft classification number (ACN) is less than or equal to the pavement classification number (PCN). A newer system, the ACR-PCR, introduced by ICAO in 2020 and effective from November 2024, improves upon this by using layered elastic analysis (LEA) to quantify pavement damage based on stress and deflection responses. This system allows for more precise assessment of pavement capacity, with restrictions imposed if the aircraft classification rating (ACR) exceeds the pavement classification rating (PCR) [38; 39; 40]. A flow chart illustrating the functional and structural condition assessment of runway, apron, and taxiway pavements within the APMS framework is shown in Figure 3. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Number of Turbojet Engine Aircraft Landings**} & **Minimum Friction Measurement** \\
**Per Runway Daily** & **Frequency** \\ \hline Less than 15 & 1.year \\ \hline
16–30 & 6 months \\
31–90 & 3 months \\ \hline
91–150 & 1 month \\
151–210 & 2 weeks \\ \hline
**More than 210** & 1 week \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Friction measurement frequency at airports. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Level**} & \multirow{2}{*}{
\begin{tabular}{c} **Degree of** \\ **Friction** \\ \end{tabular} } & \multicolumn{4}{c}{**Friction Measure (65 km/h Test Speed)**} \\ \cline{3-6}  & & & & **Airport Surface** & **Skiddometer** \\ \cline{3-6}  & & & & **Friction Tester** & **Skiddometer** \\ \hline
3 & **Acquate** & \(\approx\)0.53 & \(\approx\)0.52 & \(\approx\)0.60 & \(\approx\)0.60 \\ \hline
2 & Poor & 0.34-0.53 & 0.42-0.52 & 0.60-0.50 & 0.60-0.50 \\
1 & **Inadequate** & \(\approx\)0.15 & \(\approx\)0.12 & \(\approx\)0.54 & \(\approx\)0.54 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Friction limit values used by the FAA.