ATTACHMENTS
C.4-1: Area Navigation as an enabler
C.4-2: Understanding the ATC System: Constraint or Enabler?
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This chapter discusses Assumptions, Enablers and Constraints which constitute the second phase of the design concept.
SAFETY & PERFORMANCE ASSUMPTIONS, Compare DESIGN: ROUTES & HOLDS DESIGN: AIRSPACE & SECTORS
CRITERIA ENABLERS & CONSTRAINTS
Qualitative Assessment
As stated in Chapter 2, Assumptions, Enablers and Constraints are constants to the entire Terminal Airspace design process. They are carried through to the Assessment and Validation phases of the project (see Part D)
As suggested in previous chapters, the performance criteria, assumptions, enablers and constraints are established before the Terminal Airspace is designed conceptually or any other design phase is undertaken. Moreover, it is important to note that assumptions,constraints and enablers underpin all phases of the design process and thereforeremain constant throughout the design process (unless one of the aims of a Scenario (see Part D) is to test an assumption (or enabler, or constraint)). This requirement for consistency is illustrated below.
DESIGN METHODOLOGY
ASSESSMENT & VALIDATION
IMPLEMENTATION & REVIEW
ASSUMPTIONS
Figure 4 - 1: Consistency
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Figure 4 - 2: ATM/CNS1
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4.2.1 ASSUMPTIONS
Assumptions refer to elements of ATM/CNS which are assumed to be ‘true’ for purposes of the design. ATM/CNS covers a wide variety of fields which often requires most designers to consider factors beyond the limits of their own expertise. Assumptions may also have to be made concerning factors beyond direct ATM/CNS e.g. certain weather phenomena.
Whilst some assumptions are based upon factors/elements which can be relied upon with reasonable certainty within the time-scales of the design project, other assumptions are likely to be no more than an ‘educated guess’ [because obtaining firm knowledge is not possible within the timescales]. It is better to undertake the design process without any uncertainties, but there is sometimes no option but to include them so as not to stop or delay the overall design project.
The incorrect identification of assumptions can be the undoing of a Terminal Airspace design. It is therefore better to err on the side of caution when selecting assumptions. This can be illustrated by way of an example:
Example: Suppose that it is not possible to establish whether a ATS route will be available for traffic from X to Y, and that the absence/presence of the new route is the key to reducing the workload in a particular sector. In this case, it would be better not include the new ATS route as an assumption in the traffic sample. This said, however, it may be worthwhile to have a two-phase design plan where the first excludes the new ATS route and the second includes the ATS route, so that the true value of the new route can be quantified.
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