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between an aircraft pair in a sector) is used for analysis purposes (such as comparing two
different concepts of operations) and as input to NARIM Analysis Tools, described next.
The NARIM Analysis Tools are used to examine airspace density, proximity events, and
flight leg statistics. This NARIM component consists of a series of separately compiled
and executed programs. The first tool, Count Proximities, is used to categorize proximity
events by closing velocities. Closing velocity can be used to identify the type of proximity
event as being either a crossing conflict, head-on conflict, or overtaking conflict. The
output of this tool is stored in an ASCII file which is typically used with other desktop
tools (such as Excel) in the conduct of studies.
The second tool, Point Proximity Dot Display, generates a graphical display of proximity
events overlaid on a map of the United States. These proximity events are usually colorcoded,
based upon their relative closing velocity, to indicate the relative complexity of the
demand scenario being analyzed.
SEPARATION SAFETY MODELING
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The third tool, Load Compare, is used to compare airspace density or proximity events
occurrence rates across two scenarios or at different times within a single scenario. This
tool requires sector statistics information computed as part of the FC module. Sectors can
be either current sectors as defined by ACES data or can be user specified. Display Load
creates a geographic plot of the output of Load Compare (such as proximity event
occurrence rates, instantaneous airspace density, or airspace density over time).
The last tool, Leg Comparison, is used to compare, on a flight-leg-by-flight-leg basis, the
difference between the two input scenarios. The metrics that are currently used in Leg
Comparison are the average distance between flights over time and the length and
duration of flight legs. However, additional metrics have been evaluated and could be
included if necessary.
The Optimized Trajectory Generator (OPGEN) is used to construct wind optimized
trajectories between city pairs constrained by aircraft performance, scheduled arrival
times, desired time en route, and special use airspace avoidance constraints. OPGEN uses
subroutines contained in FC to identify whether a flight enters a special use airspace in the
baseline scenario since that identifies its availability for the wind-optimized case. The user
also has the option of specifying additional constraints such as whether to impose cardinal
flight altitude rules. OPGEN generates 4-D trajectories in the same format as Convert and
thus they can be used interchangeably by other tools within NARIM such as FC and T3.
OPGEN is used within NARIM to generate trajectories for scenarios containing aircraft
that fly point to point.
The Reorganized ATC Mathematical Simulator (RAMS) provides fast-time simulation and
conflict resolution as part of NARIM's operational modeling capability. RAMS can
perform high-fidelity investigations of aircraft conflicts that occur under different
scenarios. Inputs include sector boundaries, aircraft flight plans, aircraft performance,
SUA restrictions, and workload model task times. RAMS runs as a stand-alone
application on the workstation and is loosely integrated with other NARIM components,
meaning that its inputs and outputs are done through files. Since this model was
developed and is maintained by Eurocontrol, its integration into the NARIM architecture
will be limited to a stand-alone application that executes on the NARIM platform, an HP
workstation.
The National Airspace System Simulation Model (NASSIM) comprises the
architecture/infrastructure modeling component of NARIM. It is used to identify potential
resource demand/capacity imbalances under alternative concepts of operation. The scope
of the current NASSIM prototype is an ARTCC, a TRACON, and two airports. The
current prototype is developed in a graphical, object-oriented development environment.
Simulation objects are developed to reflect the functional behavior and performance
characteristics of elements of the NAS (such as human, hardware, and software
components). These objects may be modified to reflect changes in the characteristics or
performance of an element of the NAS, implemented through some combination of
functional enhancement and procedural changes. The objective of the current NASSIM
prototype is to evaluate the impacts of data link as an alternate media for air/ground voice
EXISTING MODELS AND MODELING TOOLS
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communications. The model generates a wide variety of performance metrics that are
stored within the model and manually extracted for use in desktop analysis tools such as
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a concept paper for separation safety modeling(43)
