## 4 Case Study: Application of APIRM Model at Istanbul Airport
### Identification of Distresses (Hazards) in Pavements  
The identification of hazards in airport pavements is an outcome of periodic monitoring and evaluation. At Istanbul Airport, runway pavements are inspected by the apron operations unit at least four times a day using a vehicle. If any deterioration is observed, a detailed assessment is requested from the construction pavement management unit. Several key measurements are performed regularly:  
Friction measurement: Due to heavy air traffic, a trailer skiddometer and a dry measurement airport surface friction tester (ASFT) are used once a week on all runways.  
Strength measurement: Initially performed using the plate loading test during the construction phase to establish pavement classification numbers (PCNs), which are then published in the Aeronautical Information Publication (AIP). This test is repeated in pavement sections that undergo rehabilitation.  
Roughness measurement: Conducted at the end of construction using a Hi-Lo device and again when necessary, such as after repairs to damaged areas (e.g., corrugation, rutting). Roughness measurements can also be repeated based on pilot complaints.  
Maintenance and rehabilitation information, as well as the results of these measurements, are systematically recorded and archived.  
According to interviews with Istanbul Airport pavement inspection experts, the primary forms of distress observed in the airport's pavements are as follows:  
Rutting and corrugation: Detected in both runway and taxiway asphalt pavements.  
Joint seal damage and corner fractures: Reported in apron and taxiway concrete pavements.  
Friction loss: Occurs due to tire contaminants in the runway touchdown zone area.  
Surface damage from fuel spills: Caused by jet fuel and fuel leakage from ground service vehicles, primarily affecting asphalt pavements.  
Notably, no issues were reported concerning the strength of the pavement.  
The distresses in the Istanbul Airport runway, taxiway, and apron pavements are evaluated using airport pavement management system (APMS) assessment criteria. In this study, three key functional status assessment methods were considered for flexible pavements (runway and taxiway):  
- Friction assessment.  
- Surface deterioration using the FAA PASER method.  
- International Roughness Index (IRI).  
Distresses (hazards) were defined based on these criteria. When a pavement reaches the most severe levels of these criteria, it is assumed to be out of service, eliminating the need for risk analysis at that stage. Table 4 contains hazard definitions based on APMS criteria levels.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Hazard No.**} & \multicolumn{3}{c}{**Evaluation Level**} & \multirow{2}{*}{**Hazard (Distress) Definition**} \\ \cline{2-2} \cline{4-5}  & **FAA PASER** & & **Friction** & **IRI** \\ \hline
1 & 5 & 3 & 4 & New pavement + no distress \\ \hline
2 & 5 & 3 & 3 & Minor corrugation or rutting in the pavement \\ \hline
3 & 5 & 3 & 2 & Partial corrugation or rutting in the pavement \\ \hline
4 & 5 & 2 & 4 & Friction loss on the pavement surface \\ \hline
5 & 5 & 2 & 3 & Friction loss on the pavement surface + minor corrugation or rutting \\ \hline
6 & 5 & 2 & 2 & Friction loss on the pavement surface + partial corrugation or rutting \\ \hline
7 & 4 & 3 & 4 & Minor deterioration in pavement structural integrity \\ \hline
8 & 4 & 3 & 3 & Minor deterioration in pavement structural integrity + minor corrugation or rutting \\ \hline \hline \end{tabular}
\end{table}
Table 4: Hazard definitions of Istanbul Airport pavements (calculated based on APMS criteria levels).