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4.3.1 CHOOSING A TRAFFIC SAMPLE
As stated previously, traffic demand refers to a traffic sample which is considered representative of the traffic servicing the airport(s) within the Terminal Airspace. This representative traffic sample is an ‘assumption’ which needs to be selected with care. Selection of a traffic sample that is most representative of the traffic within a Terminal Airspace is best achieved by combining statistical analysis with ATC experience and by looking beyond the information available. Two elements of the traffic sample are to be distinguished, which for convenience, will be described as Traffic Distribution over Time and Geographic Distribution of traffic. An appreciation of both elements is crucial to choosing a representative traffic sample.
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4.3.1.1 Traffic distribution over Time
As regards Time, a feasible starting point is a snapshot analysis of the number of movements through the Terminal Airspace by month so as to determine the regularity of the resultant graph2.
Using the sample graphs below (of three fictitious Terminal Airspaces) the following information can be drawn: Where Terminal “A” has a graph that is characteristic of large Terminal Airspaces in the core area, Terminal “B” is typically representative of summer holiday resorts and Terminal “C” typical of winter holiday (ski) resorts.

Graph 4 - 1: Distribution of Traffic over Time
Whilst in the case of Terminal “A” it is obvious that one day’s traffic (the traffic sample) should be selected from one of the busier months, airspace design planners for Terminals “B” and “C” may wonder whether selecting one day during the busiest month truly constitutes a representative traffic sample. Because two busy months of the year may not be ‘representative’, airspace designers from these two Terminal Airspaces would do well to select two traffic samples i.e. one day from the busy months and one day from the quieter period.
The advantages reasons for this are two fold:
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to enhance the potential to apply the Flexible Use of Airspace concept (see Part A, Chapter 2 and Sections 1 and 3 of the EUROCONTROL Manual for Airspace Planning).

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if the geographic spread of the traffic is significantly different during the ‘quiet’ and ‘busy’ months, it may be necessary to create two sets of Terminal Routes;

2 It is also useful to ascertain the ‘busiest day’ of the year determined annually by EUROCONTROL.
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Comment: Is it viable to create two (or more) sets of Terminal Routes to accommodate significant changes in traffic density and/or distribution? Opinions diverge as to how significant changes in the operating environment should be accommodated. Whilst one view holds that an ‘unstable’ or ‘changeable’ airspace structure is to be avoided, the opposing view contends that it is not only possible but desirable to use airspace in a flexible manner. Whatever the philosophy followed, designers should ensure that the design fully supports safe and orderly air traffic management.
4.3.1.2 Geographic distribution of traffic
Having selected a one-day traffic sample from a Time perspective (i.e. one that is representative of periods of high and low activity), it is necessary to determine the geographic distribution of this traffic with a view to identifying the predominant and secondary traffic flow(s). To this end, the traffic sample needs to be analysed using, for example, a spreadsheet. Because traffic data files contain information on each flight, flights can be sorted in several ways, e.g. –
　
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本文鏈接地址：EUROCONTROL MANUAL FOR AIRSPACE PLANNING 2(27)