Aerospace and Electronic Systems Magazine April 2018 - 42

Simulation Modelling of Traffic Collision Avoidance System
agement system safety net, the pilot plays a considerable role as a
complement to TCAS in the process of collision avoidance, and
this agent overseeing the interactions of the sophisticated sociotechnical system TCAS is essential.

To overcome the shortcomings
of TIMSPAT and CPN Tools and
combine their advantages, the

AGENT MULTI-THREAT ESTIMATION
Agent multi-threat estimation has one nested function component
h1′ as a submodel to screen out the approaching aircraft, and three
function components (h8, h9, and h10) to check whether a secondary
conflict exists in the possible future situations. It integrates with
Agent aircraft TCAS to obtain the state of related aircraft in the respective collision avoidance process. Through generating the state
space of a specific multi-aircraft scenario, not only the potential
domino threat can be identified, but also the optimal combination
of advisories can be achieved.
The nested function components h1′ contains three function
′ , and h1,3
′ ) that severally select the neighboring
components (h′1,1, h1,2
threats, screen the approaching aircraft, and make the pair of aircraft between which there would be an interrelationship that may
lead to a new secondary conflict. It is ingeniously designed to narrow the expanded state space and would play an important role
in dealing with the complex multi-aircraft scenarios (e.g., flocks).

RESULTS
Table 1 provides the relevant parameters used in the different experiments to validate the feasibility and analyze the property of the
GMAS-based encounter model. TCAS II Version 7.1 is utilized
as the equipment in these simulations, thus the initial/subsequent
RA acceleration, initial primary/subsequent pilot delay and other
parameters are accessible in [6].

SCENARIO EVALUATION WITH WIND DISTURBANCE
The three-aircraft scenario is shown in Figure 1. Based on the radar
data from the FAA and Department of Defense sites throughout
the United States [19], over 95% of the 3.803 multi-threat encounters involve three aircraft, and they also involve the interrelationship (also called domino effects) between neighboring threats. For
instance, a new secondary threat between UAV2 and UAV3 may

GMAS was developed. GMAS
is a powerful graphical and
mathematical modelling tool.
emerge in the process of resolving the initial conflict. Therefore,
the typical case scenario used in this article is appropriate for exploring a multi-aircraft scenario that involves wind disturbance.
At 9:36:56, Aircraft 1 is cruising at (10.27 NM, 4.73 NM) in
FL 151 with a ground speed of 460.0 kt; Aircraft 2 is at (23.02
NM, 4.73 NM) with a ground speed of 613.0 kt and descends from
FL160 with a vertical speed of 100.0 fpm; Aircraft 3 is at (4.03
NM, 4.71 NM) with a ground speed of 653.0 kt and climbs slightly
from FL150 with a vertical speed of 120.0 fpm.
First, we shield the Agent wind disturbance without consideration of the influence of wind. For resolving the threat between
Aircraft 1 and Aircraft 2, the TA is to fire a warning at 9:37:01.
As the situation is getting worse, an RA emerges 15 seconds later
to ask the crew of Aircraft 1 to descend and the crew of Aircraft
2 to climb at 9:37:16. Note that in this RA process, the climbing
Aircraft 2 would not encounter Aircraft 3.
Then, the Agent wind disturbance is taken into account and the
wind speed V30 is assumed to be 90 kt with the opposite flight direction of Aircraft 1. The initial threat between Aircraft 1 and Aircraft 2 still exists, and the TA is to fire a warning at 9:36:59 while
RA is at 9:37:14. At first, Aircraft 3 does not contain a threat with
Aircraft 2. However, they encounter each other as a result of the
amended flight level of Aircraft 2. Table 2 illustrates the waypoints
of a partial trajectory of each aircraft before the secondary threat
occurs between Aircraft 2 in the upward sense and Aircraft 3 in
the cruising flight. Because the flight direction of upward Aircraft

Table 1.

Parameter Values for the Scenarios
TCAS
Equipment

Initial RA Acceleration (g)

Subsequent RA
Acceleration (g)

Initial Primary Pilot Delay (s)

Subsequent
Pilot Delay (s)

TCAS II 7.1

0.25/-0.25

0.35/-0.35

2.5

Tau (s)

DMOD (NM)

ZTHR (feet)

ALIM (feet)

SL
6

1.00

0.80

850

600

400

IEEE A&E SYSTEMS MAGAZINE

APRIL 2018

Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine April 2018