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This guideline aims to simplify the route structure within Terminal Airspaces by ensuring that the complex task of traffic merging is done outside the Terminal Airspace (which is usually constrained in size).
Whilst the merging of arrival traffic flows should (ideally) be accomplished outside the Terminal Airspace, this does not suggest that the Terminal Airspace should only have four entry points. Indeed, there are two well known instances where it is desirable not to merge the arrival flows towards a common point. These are –
.  
where the aircraft performance mix is such that there is a marked speed difference in a large percentage of the traffic; or (/and)

.  
where the Terminal Airspace contains several major airports.

In either of the above cases, it is usually better to merge the arrival flows towards what might be called entry gates, each of which may contain arrival flows which are segregated either for different performance or for different airport destinations. In exceptional circumstances, it may even be necessary to split a common arrival flow into segregated routes inside the Terminal Airspace, especially to segregate different aircraft (speed) performance.
To appreciate the difference between merging arrival flows merged towards one entry point and one entry gate, where arrival routes remain segregate to accommodate different aircraft performance, (a) and (b) of Figure 5- 12 can be compared. Similarly, Figure 5- 12 can be compared to diagrams in Chapter 7.
Note: This Guideline does not suggest that Terminal Airspace exit points should be limited in number. See illustration at para. Figure 5- 6.
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