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to the level of human controller tasks (air and ground), air traffic procedures, and
technical ATM/CNS (Air Traffic Management / Communications, Navigation,
Surveillance) systems. Starting from a less detailed description is possible. In this
case, the safety evaluation results will be less precise, but when comparing conceptual
designs this might even be an advantage.
· Statistical characterization of the air traffic scenarios to be evaluated; i.e. traffic
flow(s), aircraft types, etc.
· Identification of all relevant hazards, including a qualitative evaluation of their effects.
This is accomplished through executing a preliminary hazard analysis that pays proper
attention to all possible sources of non-nominal events (human, procedural, and
technical systems).
SEPARATION SAFETY MODELING
6-10
· Develop a high-level Petri net model for the operational concept to be evaluated. This
high level-Petri net model should be of sufficient detail to represent all event sequences
which may play a critical influence on the safety/capacity assessment.
· Identification of parameters or parameter ranges for all elements that may have a
critical influence on the safety/capacity assessment. This is accomplished through
collecting statistical data from appropriate data bases and through assessing the
allowable ranges of the design parameters.
Outputs Produced
With the help of TOPAZ, it is, in principle, possible to evaluate the safety characteristics
of any (new) operational ATM concept under consideration, with respect to safetycritical,
non-nominal event sequences. The outputs provided consist of frequencies for the
occurrence of non-nominal event sequences and conditional probabilities of collision (or
hull loss) for different types of non-nominal event sequences. The practical interpretation
of these figures is supported by a tree-wise representation, with an overall risk measure at
the top. If desired, TOPAZ executes safety assessments as a function of scenario
parameters, such as traffic flow.
Major Assumptions and Limitations
The main limitation is that for every instantiation of an operational ATM concept, TOPAZ
will often need an appropriate adaptation of already available, high-level Petri net
modules. For such adaptation, a high level of expertise is required from multiple domains
(stochastic modeling, human factors, and air traffic expertise).
Computational Characteristics
TOPAZ runs on a personal computer (PC); a powerful one is preferable when running
Monte Carlo simulations.
Modularity and Flexibility
TOPAZ is a highly modular and flexible system.
Status
TOPAZ is under continual development for application to advanced operational ATM
concepts. In mid-1996, TOPAZ had reached a certain level of maturity for the safety
assessment of Dependent Converging Instrument Approaches (DCIA) with the help of
MITRE’s Converging Runway Display Aid (CRDA). The most recent development has
incorporated models of human cognition based on E. Hollnagel’s approach to human
reliability analysis [R6.2].
EXISTING MODELS AND MODELING TOOLS
6-11
Extent of Model Verification
The software implementations of the high-level Petri net and the Generalized Reich
collision risk models have been verified for correctness. For this, extensive use was made
of the mathematical basis of these models. Beyond this level, the results obtained were
corroborated through discussions with experts.
Principal Applications
· DCIA/CRDA safety assessment for Schiphol airport Amsterdam [R6.3]
· Analysis of advanced ATM concepts in Europe (to be done in TOSCA II, phase 2)
· P-RNAV route separation safety assessment [R6.4]
· Safety-based, Free Flight concept design
· Safety-based design of airport/Traffic Maneuvering Area (TMA) procedures
· Safety controllability by human operators [R6.5]
· Safety assessment of collisions due to wake vortices
Availability
TOPAZ is constantly being updated and improved. It is available through the National
Aerospace Laboratory NLR in the Netherlands, PO Box 90502, 1006 BM Amsterdam.
Contact: Henk Blom, phone: +31.205113544, blom@nlr.nl. The most recent information
on TOPAZ can also be obtained from this source. Information about TOPAZ can also be
found on the Internet. See http://www.nlr.nl/public/news/f151-01/index.html.
6.3 THE NATIONAL AIRSPACE RESOURCE INVESTMENT MODEL
(NARIM)
Introduction
The National Airspace Resource Investment Model (NARIM) is being developed jointly
by the Federal Aviation Administration (FAA) and the National Aeronautics and Space
Administration (NASA). The purpose of NARIM is to provide NASA and the FAA with
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a concept paper for separation safety modeling(41)
