# Hub Airport End-Around Taxiway Construction Planning Development: A Review
## 5 Sunken End-Around Taxiway and Terrain Shielding  
The construction of EAT must meet the tail height requirements of applicable aircraft. According to ICAO Annex 14 and flight procedures, the distance between the EAT and runway end needs to exceed 600 m for Category C aircraft and 1000 m for Category E aircraft, whether for SAT or REAT. The SAT and operating aircraft should not obstruct lights, typically over 960 m away. However, an excessively distant EAT reduces taxiing efficiency. Therefore, reducing the distance between the end-around taxiway and the runway threshold presents challenges and is a key focus in end-around taxiway design. In practice, the primary method is to greatly increase the elevation difference between the end-around taxiway and runway threshold, making the end-around taxiway elevation significantly lower than the runway threshold elevation and making it serve as a sunken end-around taxiway. Following the 2% obstruction clearance limit, the end-around taxiway can be displaced 50 m inward for every 1 m reduction in elevation. For REATs, since there is no need to consider the shielding of lights by aircraft operating on the end-around taxiway, coordination of terrain, approach lighting slope, and other means can enable successful inward movement of the end-around taxiway. For SATs, the runway entrance and approach lights must shift inward to prevent operating aircraft from blocking lights and allow end-around taxiway inward displacement. The addition of metallic visual screens makes the inward displacement of end-around taxiways more complex and difficult. Their height cannot obstruct approach lights, and they themselves cannot impact the sensitive and critical areas of the ILS. In recent years, with more research in this area, end-around taxiway design schemes in China have adopted sunken end-around taxiways and terrain shielding. Terrain shielding utilizes terrain elevation changes between the runway threshold and the end-around taxiway. The aim is for pilots to only see upper aircraft parts of aircraft engines on the end-around taxiway when taking off from the runway V1 point. Terrain shielding does not need to consider the impact of metals on signals. It only accounts for requirements of the runway end safety area, ILS facilities' critical and sensitive areas, and approach lighting height changes. The introduction of terrain shielding simplifies the originally complex metallic visual screens that require multifaceted evaluation. This promotes the application of end-around taxiways at major hub airports. Together with sunken end-around taxiways, it reduces taxiing distance. In recent years, the end-around taxiway designs for airports like IST, \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**ICAO Code** & \begin{tabular}{c} **End-Around Taxiway** \\ **Classifications** \\ \end{tabular} & **Location** & **Horizontal Geometry** & **Vertical Geometry** \\ \hline DFW & REAT & \begin{tabular}{c} 360 m from the runway \\ south threshold, 400 m \\ from the \\ north threshold \\ \end{tabular} & 217.3 m & 6.1 m \\ \hline DTW & REAT & \
\begin{tabular}{c} 515 m from the runway \\ threshold, 360 m \\ beyond the physical \\ end of the runway \\ \end{tabular} & 216 m & 6.1 m \\ \hline SHA & REAT &
\begin{tabular}{c} 388 m from the runway \\ threshold, 688 m \\ beyond the physical \\ end of the runway \\ \end{tabular} & 240 m & 6 m \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Summary of metallic visual screens in use. Xi'an Xianyang International Airport, Jinan Yaoqiang International Airport, and Guiyang Longdongbao International Airport (KWE) in China have considered this method [61; 93]. Take KWE as an example. Guiyang Airport has just undergone a large-scale expansion, building a new parallel runway based on the existing one. The original runway was extended by 300 m, with a Sunken SAT end-around taxiway set outside the runway end. The sunken SAT has innate advantages at KWE.