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Excel.
Insight5D comprises the investment analysis modeling component of NARIM. The
Insight5D prototype incorporates a methodology, referred to as Integrated Response
Surface Modeling (IRSM), used by the U.S. Department of Defense (DOD) on its
advanced programs. The core concept is to build up a hierarchy of response surfaces. At
each level, a surface represents the interactions and tradeoffs among system performance
parameters. The values associated and the surface defined by the relationships between
performance parameters is determined either through an analytic formula or through
multiple runs of a simulation model. The interaction of parameters at one level will define
a new set of parameters at the next higher level and a surface is developed to show the
tradeoffs among these parameters. The hierarchy and the surfaces allow the decision
maker to determine visually how tradeoffs can be made and how a decision at the top level
is reflected in regions of tradeoffs at each lower level.
6.4 THE INTERNATIONAL CIVIL AERONAUTICS ORGANIZATION
(ICAO) COLLISION RISK MODEL
The International Civil Aeronautics Organization (ICAO) provides guidance for separation
analysis (e.g., [R6.6]). It has adopted a collision risk model developed by the North
Atlantic System Planning Group (NAT SPG) to evaluate the safety implications of varying
separation standards in the North Atlantic Oceanic Track System (NAT OTS). The
newest North Atlantic separation standard (60 NM lateral and 1,000 ft vertical) was
arrived at by using this model together with a set of Minimum Navigation Performance
Standards (MNPS) that aircraft must meet if they intend to fly in airspace covered by the
new separation minima. The model is adapted from the original Reich separation model
[R6.7].
Main approach
In the collision risk scenario, one aircraft blunders from its own assigned path into airspace
that is assigned to other air traffic. The collision risk is essentially the product of the
probability of the blundering aircraft occupying a small volume of airspace and the
probability of one of the other aircraft occupying the same airspace at the same time. The
airspace occupied by an aircraft is approximated by a three-dimensional box. Equation (1)
indicates the general approach to computing the probability of collision.
P(collision) @ Py(Sy)•Px(Sx)•Pz•[traffic density factor] (1)
The main factors are the lateral overlap probability Py(Sy), a longitudinal overlap
probability Px(Sx), a vertical probability Pz, and a traffic density factor. The parameter Sy
represents the (proposed) minimum lateral separation between adjacent oceanic tracks.
The parameter Sx represents the (proposed) minimum indicated separation between
SEPARATION SAFETY MODELING
6-16
consecutive aircraft at the same altitude on the same track in the same direction. The
criteria for allowing a particular separation minimum is that the probability of collision
does not exceed a fixed target level of safety.
Lateral deviations are modeled as a double-double exponential probability distribution
with parameters derived from historical data. This distribution is a mixture distribution
that combines a probability distribution of deviations due to avionics and flight
management systems with one of deviations due to blunders.
The primary model inputs are the traffic density and lateral navigation performance.
Traffic density is defined in terms of same and opposite direction traffic at the same flight
level. Navigation performance is defined by three terms - standard deviation, proportion
of flight time exceeding 30 nm deviations, and proportion of flight time between 50 and 70
nm deviations. The output of the model is the risk of collision, expressed as the expected
number of collisions per 107 flying hours.
6.5 BOEING ADS STUDY
The reference [R6.8] reports a study that was done by the Boeing Air Traffic Control
Systems Analysis Group that addresses the application of Automatic Dependent
Surveillance (ADS) to oceanic aircraft tracking.
Purpose and application
This study analyzed both lateral and longitudinal separations in the North Atlantic oceanic
tracks as a part of estimating the benefits of ADS. Lateral modeling in the study slightly
generalizes the work of ICAO [R6.6], Reich [R6.7], and others. The longitudinal
modeling is based on the sum of three separation parameters: intervention rate, tactical
control response, and surveillance accuracy. The study estimated how much more tightly
oceanic traffic could be packed, both laterally and longitudinally, without compromising
existing levels of safety.
Main approach
In the lateral analysis, the ICAO Collision Risk Model is used without changing its form.
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a concept paper for separation safety modeling(44)
