# Hub Airport End-Around Taxiway Construction Planning Development: A Review
## 4 The Construction Principles and Key Points of End-Around Taxiway Layout
### Visual Impediment  
Visual impediments are inherent to REAT operations. As the taxiing aircraft crosses in front of the departing aircraft, visual separators between the runway end and REAT are required to obscure aircraft on the REAT from the pilots' view. This prevents confusion with any incursion aircraft at the runway end, allowing pilots to clearly distinguish between normal bypass taxing and potential runway incursions. FAA pioneered research into visual screens, constructing the first one with metallic materials. In 2007, through a field trial at the ATL end-around taxiway case [89], the FAA evaluated visual screen materials, structures, patterns, colors, and lighting methods via pilot questionnaires. Guidance on siting and implementing visual screens was finally provided in AC150 [67] and its attachments, based on this evaluation; Figure 15 demonstrates end-around taxiway screen sizing and location [67], Figure 15 shows the End-around taxiway screen sizing and location guidance in AC150. The world's first visual screen was born at DFW. In 2021, DFW also installed visual screens in front of the north REAT. (1) Horizontal Geometry: Base the design of the screen width on a departing aircraft's view from a location at the V1 point through the farthest point on the runway hold line at the departure end of the runway. \[\angle\text{A}=\text{arcta}\ \frac{D_{h}}{D_{v}} \tag{1}\]  
\[(\tan\angle\text{A}(D_{v}+D_{d}))=0.5D_{e} \tag{2}\]  
where: \(D_{v}=0.4\ \times\) runway length  
\(D_{d}=\) Distance from the departure end of the runway to the screen  
Figure 15: End-around taxiway screen sizing and location [67]. \(D_{h}=\) Distance from the runway centerline to the hold line  
\(D_{e}=\) Width of the EAT Visual screen  
(2) Vertical Geometry: Design the height of the screen so that the top of the screen masks that portion of an aircraft that extends up to the top of an engine nacelle of the ADG taxiing on the EAT, as viewed from the cockpit of the same ADG at the V\({}_{1}\) point on the departure runway. \[\mathrm{H_{S}}=\frac{\mathrm{ELEV_{v1}}+\mathrm{H_{FYE}}-\mathrm{ELEV_{EAT}}- \mathrm{H_{NACELLE}}}{\mathrm{D_{EAT}}+0.4\times\mathrm{L_{RRVY}}}\times( \mathrm{D_{EAT}}-\mathrm{D_{d}})+\mathrm{H_{NACELLE}}+\mathrm{ELEV_{EAT}}- \mathrm{ELEV_{GAS}} \tag{3}\]  
where:  
\(\mathrm{ELEV_{VI}}=\) MSL elevation of the runway centerline at the V\({}_{1}\) point, 60%of the length of the runway from the takeoff threshold  
\(\mathrm{H_{FYE}}=\) Height of the pilot's eye above the runway  
\(\mathrm{H_{NACELLE}}=\) Height of the engine nacelle above the taxiway  
\(\mathrm{ELEV_{EAT}}=\) MSL elevation of the centerline of the EAT  
\(\mathrm{D_{EAT}}=\) Distance from the departure end of the runway to the screen  
\(\mathrm{L_{RRVY}}=\) Length of the runway  
\(\mathrm{ELEV_{GAS}}=\) MSL elevation of the ground at screen  
AC150/5300-13B also provides basic specifications for the material and composition of visual screens. However, sitting metallic visual screens is extremely challenging for two primary reasons:  
Firstly, the screens are situated between the runway end and REAT; thus, the metal's unique properties may impact critical and sensitive areas for ILS and approach lighting systems [43; 90; 91]. These areas should be avoided, if possible, but even after successful avoidance, subsequent relevant testing cannot be precluded, as large metallic surfaces can potentially induce signal effects that are difficult to predict. Secondly, while visually blocking pilots' sightlines, the screens must not obstruct signals for approach lights and navigation antennas. Concurrently, the screens cannot penetrate any obstacle limitation surfaces either. Therefore, after location selection, meticulous calculations are required to determine permissible width and height. Although the FAA provided some recommendations, the actual implementation of metallic visual screens is complex and sometimes nearly infeasible to replicate. Nonetheless, the FAA's fundamental research on aspects like materials and colors remains constructive.