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As a methodology, Fast-Time simulation is a valuable and frequently used way of validating a proposed design and it may also be used as a way of demonstrating that the safety objectives have been met.
Very often, designers use fast-time simulation as a first step in the validation process i.e. prior to real-time simulation, but also it might be the only step used to validate the concept. Because fast-time simulation is less demanding than real-time simulation in term of human resources, this is often a preferred method for improving the proposed design, identifying flaws in the design concept, and/or preparing the path to real-time simulation or direct implementation.
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As with all simulation tools, Airspace Organisation and Traffic Sample need to be defined for the simulated environment using specific computer language and conventions. To simplify the explanation which follows, various parameters of the Airspace Organisation and Traffic Sample are discussed under separate headings.
4.2.1 ROUTES
Usually, any route in a FTS is defined by linear segments between points. The aircraft model follows the planned turns in the route according to the aircraft performance defined in the aircraft performance database used by the Traffic Sample. Because FTS flight trajectories are computer generated models, all aircraft naturally follow, with maximum accuracy, the planned flight trajectory unless, deviations are specifically programmed into the trajectory.
Additionally, routes in the FTS have associated vertical constraints used to model a realistic behaviour of the aircraft in the vertical dimension (These are types of Rules in the Traffic Sample). These constraints could be generally applicable to all aircraft or defined on a flight-by-flight basis. For their part, tactical manoeuvres (e.g. radar vectors) are replicated by the creation of a set of fictional routes which are designed to overlap the tactical allocated paths.
Some simulators can use imported real-radar data and the extracted trajectories can be used in simulation.
Figure 4 - 1: Sample FTS Route definition
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4.2.2 TERMINAL AIRSPACE STRUCTURES AND SECTORS
The same logic is applicable to the airspace modelling of Terminal Airspace Structures and ATC Sectors: the airspace is represented by blocks defined by a horizontal shape and height. In this respect, functional sectors are difficult to model. A way around is to define fictional blocks of airspace for each functional sector and assign the specific controller task to each one.
4.2.3 RULES
In a FTS the behaviour of aircraft is dictated by a series of rules which are generally defined for some or all Test Cases or specifically for each block of airspace, route segment or waypoint. Without these rules, the simulated aircraft will fly their optimum profiles according to their flight plan which seldom reflects real life operation.
Rules are used by the simulator engine to mimic pilots and ATC actions, such as:
　
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