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The identification and selection of assumptions is likely to provide the greatest challenge to the designer in the case of futuristic design projects e.g. creating a Terminal Airspace model for the year 2025 for a new airport site with eight parallel runways. As most designers can vouch, the closer the implementation date the easier the assumptions are to select. In the case of futuristic projects, the designer may be left no choice but to use educated guesswork
– and ensuring that the final report properly reflects this.
4.2.1.1 Traffic Assumptions
Assumptions made concerning the traffic demand in the Terminal Airspace and those made concerning the predominant and secondary runway(s) in use are of crucial importance to the design of a Terminal Airspace. Traffic demand and runway(s) in use are important because the notion of Terminal Airspace includes the ‘resultant’ airspace created to protect
1 Derived from International Civil Aviation Vocabulary, ICAO Doc. 9713 (2001), Part 1
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IFR flight paths to and from the runway(s) in use. For this reason, it is imperative that the designer:
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properly analyses the traffic demand; and

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the predominant and secondary runway(s) in use, their mode of operation and any conditions attached thereto are established.

In context, traffic demand refers to a traffic sample which the design team considers representative of the traffic servicing the airport(s) within the Terminal Airspace. Thus the representative traffic sample chosen by the design team is the ‘assumption’ and it is this assumption that requires thorough analysis prior to commencing the design process.(How the traffic sample is selected is discussed in para. 4.3.1).
Whilst traffic demand inevitably refers to a traffic sample, a traffic sample may need to be created to cater for futuristic Terminal Airspace design projects e.g. a concept design for the year 2025. In such a case future market analyses are undertaken and a traffic sample created for airspace design purposes. (see para. 4.3.1.1).
4.2.1.2 Runway in use
Similarly, identifying the predominant and secondary runway(s) in use requires assumptions to be made as to which runway orientation is used for the greater part of the day (e.g. RWY20 is used 70% of the time as opposed to RWY02). (How to determine the predominant and secondary runway is discussed in para. 4.3.2)
This important relationship between runway in use and traffic flows explains why the addition of a new runway within a Terminal Airspace invariably results in the need for some modifications being made to the Terminal Airspace design.
4.2.2 CONSTRAINTS
Constraints stand in contrast to assumptions in that they suggest the absence of certain elements of ATM/CNS or limitations created by extraneous factors. Typical constraints include high terrain, adverse weather patterns, the requirement to satisfy environmental needs (which dictate, for example, the noise-preferential runway to be used at night time) or the absence of rapid-exit-taxiways which may limit the landing rate and therefore influence route placement. In general terms, constraints can be said to have a negative impact upon the ATC operational requirements of a Terminal Airspace design. At best, it may be possible to mitigate the constraints using enablers. At worst, constraints have to be accepted because there is no alternative ‘solution’.
4.2.3 ENABLERS
Enablers refer to any aspects of ATM/CNS that may be used to mitigate the constraints identified and/or any factors which may be relied upon to ‘enable’ ATC operations in the airspace designed. Importantly, the identification of enablers may take the form of functional requirements (which are then ‘translated’ into technical requirements) which require follow up work on the part of the ANSP and may be outside the scope of the design project – see Figure 4 - 3 and Table 4 - 1
　
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