# Hub Airport End-Around Taxiway Construction Planning Development: A Review
## 4 The Construction Principles and Key Points of End-Around Taxiway Layout
### Limiting Requirements in End-Around Taxivany Design
#### 4.3.2 REAT, Runway End-Around Taxiway Mode
The elevation of these lights may align with the terrain, which may not meet the required slope ratio of 1:66 for ascent or 1:40 for descent. Therefore, meticulous coordination between terrain design and light elevation is necessary to ensure compliance with the relevant specifications. The REAT mode also needs to consider visual screens. Metal visual screens and terrain shielding are commonly used in practice. The impact of metal visual screens on the ILS signal should be taken into account. Regardless of the chosen method, the height of the visual screen must satisfy both the requirement to shield the aircraft engines when taxiing on the REAT and to ensure unobstructed observation of approach lights by the pilot. These interdependent requirements make the elevation of this area complex and often a critical factor in determining the feasibility of REAT planning. SAT, Start-Around Taxiway Mode, Unrestricted EAT  
SAT (Start-Around Taxiway) is constructed before the runway entrance, enabling aircraft on SAT to taxi undisturbed without disrupting approaching aircraft. The SAT integrates the capabilities of both EAT and BAT, functioning as an unrestricted end-around taxiway with full functionality. 1. Appendix 14 Obstacle Limitation Surfaces  
The SAT as an unrestricted EAT requires consideration of numerous constraint surfaces; constraint surfaces previously analyzed for REAT will not be revisited here. Only constraints imposed by SAT end-around taxiing aircraft on approaching aircraft are examined: the conical clearance surface, inner horizontal surface, approach surface, inner approach surface, transitional surface, inner transitional surface, and balked landing surface. It should be noted that for REAT, taxiing occurs prior to aircraft takeoff; thus, the datum point is the runway end. For SAT, taxiing is under the arriving aircraft, so the datum point is the runway threshold [87]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**CODE**} & \multirow{2}{*}{**Aircraft Type**} & \multirow{2}{*}{\
\begin{tabular}{c} **Vertical Tail** \\ **Height** \\ \end{tabular} } & \multicolumn{2}{c}{
\begin{tabular}{c} **Distance from the Runway** \\ **End to the REAT** \\ \end{tabular} } & \multicolumn{2}{c}{**Half-Width in the Vertical Direction**} \\ \cline{3-6}  & & & \multicolumn{1}{c}{**Determined by 2\%**} & \multicolumn{1}{c}{**Takeoff Climb**} & \multirow{2}{*}{**OIS**} & \multirow{2}{*}{**Type A Surface**} \\ \cline{3-6}  & & & \multicolumn{1}{c}{**Climb Surface**} & & & \\ \hline C & A320 & 12.08 & 664 & 165.5 & 249.6 & 256.0 \\  & B737 & 12.7 & 695 & 169.4 & 254.3 & 263.8 \\ \hline D & B757 & 13.74 & 747 & 175.9 & 262.1 & 276.8 \\  & B767 & 16.13 & 866.5 & 190.8 & 280.0 & 306.6 \\ \hline E & B747 & 19.6 & 1040 & 212.5 & 306.0 & 350.0 \\  & A340 & 17.93 & 956.5 & 202.1 & 293.5 & 329.1 \\  & A330 & 18.3 & 975 & 204.4 & 296.3 & 333.8 \\ \hline F & A380 & 24.27 & 1273.5 & 241.7 & 341.0 & 408.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Half-widths of the REAT in the vertical direction of the runway (meters). For most runways, the takeoff end and opposite direction threshold coincide. However, due to the demanding obstacle limitation surface requirements for end-around taxiways, many airports displace the threshold or runway end depending on the taxiway type (SAT or REAT). Inner transitional surface: due to their steep gradients and location primarily lateral to the runway, the inner transitional and transitional surfaces do not constrain end-around taxiways. Approach surface: for aerodromes with runway codes 3 or 4, the approach surface starts 60 m from the threshold, with an initial width of 280 m, divergence of 15%, and first segment length of 3000 m (the end-around taxiway range) at a 2% slope [70]. The inner approach surface begins at the same starting point as the approach surface, with a width of 120 m, length of 900 m, and gradient of 2%. The spatial extent of the inner approach surface is less than that of the full approach surface [70].