Continuation of Qualitative and Quantitative Assessment
To better analyse the situation in Sector SA, the Terminal Airspace design team continues its assessment (both qualitative and quantitative), using primarily, information obtained during the critical review.
(a)  
Use an airspace modeller to study the actual profile of flights operating on Routes 1, 2 and 6. (See Part D, Chapter 3).

(b)
Use a flight simulator of the most representative aircraft type to determine the unconstrained profiles for flights operating on Routes 1, 2 and 6 (see Part D, Chapter 6).

(c)  
Study transfer of control and communications agreements between sector SA and adjacent sectors are studied;

(d)
Check the traffic sample to establish the point of origin for most flights that use Routes 1 and 3;

(e)  
Investigate whether the early left turn on RNAV/SID Route 2 is efficient or whether it causes difficulties between sectors SA and SD.

(f)  
Assess whether the merging of routes on final approach RWY 27 at A is generating a high workload is assessed;

Sample findings
The data produced by the investigation of items (a) and (b) reveals that actual flight profiles are very close to unconstrained flight profiles. For example, traffic on –
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Route 1, crosses X at FL60 or below;

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Route 2, crosses X at above FL50;

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Route 6, crosses X between FL40 and 50

What this finding shows is that the problem at crossing point X has not been ‘created’ by imposed flight level restrictions e.g. prescribed by ATC. Thus, as the problem is not in the vertical plane, this may indicate that the solution lies in relocating some of these routes.
Whilst information from (c) reveals no special difficulties (apart from transfer arrangements concerning RNAV/SID 2, information obtained from enquiry (d) reveals that traffic using Route 1 has a point of origin that is due west of airport C. This suggests that Routes 1 and 3 are unnecessarily merged to meet at the arrival point of sector SA – and then split for destinations C and A. (A VOR is located at this merge point which suggests that this merge point is more a historical legacy than a requirement).
As regards (e), it would seem that the controllers of sector SD believe that the amount of time available to effect a proper transfer of control and communication from sector SD to sector SA is inappropriate, given the current positioning of the sector boundary.
In turn, investigations concerning (f) suggest that the traffic merging on final approach is manageable because aircraft on RNAV/STAR 3 are often extended on down-wind by ATC (which explains the extra space in the eastern part of sector SA.
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Proposed way forward
Based on the above information, the Terminal Airspace design team decides that they have several alternatives. After considerable debate (i.e. a qualitative review of the options), they are left with two viable options:
[i]  re-design RNAV/SID 2 so that aircraft will be ‘forced’ to cross X at a higher level than is currently the case; or
[ii]  re-design RNAV/SID 2 so that it does not proceed over X; (this will require a new entry point to be created for SA) and a new route for RNAV/STARs 1 & 3 (which also avoids unnecessary merging at the western entry point).
Because (ii) is considered the better option by the Terminal Airspace design team, this Scenario is selected for further development as a Test Case – see diagram below.
　
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