Aerospace and Electronic Systems Magazine April 2018 - 36

Feature Article:

DOI. No. 10.1109/MAES.2018.170044

Simulation Modelling of Traffic Collision Avoidance
System With Wind Disturbance
Jun Tang, National University of Defense Technology, Changsha, China and Universitat
Autònoma de Barcelona, Sabadell, Spain
Feng Zhu, National University of Defense Technology, Changsha, China and Imperial
College, London, UK
Linjun Fan, National University of Defense Technology, Changsha, China

INTRODUCTION
Traffic collision avoidance systems (TCASs) are accepted worldwide as last-resort means of reducing the risk of midair collisions
between aircraft [1]. Before deploying the different versions of the
constantly evolving TCAS and because of the potential for catastrophic errors, rigorous analyses organized by several civil aviation authorities, e.g., the Federal Aviation Administration (FAA)
and EuroControl, are required [2]. A combination of elaborate
flight tests and considerate simulation studies are performed to ensure system effectiveness and safety.
In particular, due to the constraints of time, cost, and safety, simulation studies act as the main means to test the robustness of TCAS in
most situations while only a relatively few situations can be evaluated
through actual flight tests [2]. A simulation model is built for specific
study objectives and its credibility is judged with respect to those
objectives [3]. Extensive sampling of situations from a statistical
model of air traffic conflicts, commonly called the encounter model,
provides a test of the system's performance in generated pairwise correlated threats. In collision risk, an encounter model based on TCAS
logic is representative of what actually occurs in the airspace.
Authors' current address, College of Systems Engineering,
National University of Defense Technology, Changsha 410073,
China, E-mail: (zhufeng@nudt.edu.cn). J. Tang is also with the
Department of Telecommunication and System Engineering,
Universitat Autònoma de Barcelona, Sabadell 08202, Spain. F.
Zhu is also with the Department of Computing, Imperial College London, London SW7 2AZ, UK.
The authors declare that there is no conflict of interests regarding the publication of this article. Jun Tang and Feng Zhu
contributed equally to this work. This work has been financially supported by the National Natural Science Foundation
of China 71601181, the Hunan Provincial Natural Science
Foundation of China 2017JJ3357, the National Defense Science and Technology Project Fund 3101175, and the CICYT
Spanish program TIN2014-56919-C3-1-R.
Manuscript received February 3, 2017, revised and ready for
publication May 23, 2017.
Review handled by M. Jah.
0885/8985/18/$26.00 © 2018 IEEE
36

TCAS executes independently of ground-based systems, and
it relies fully on composite surveillance equipment (e.g., Mode S
and modified Mode C) [4] on-board the aircraft. The International
Civil Aviation Organization has defined and approved TCAS I and
TCAS II, an improved version of TCAS I. They differ primarily in
their alerting capability. TCAS I provides traffic advisories (TAs)
to assist the pilot in the visual acquisition of intruder aircraft, while
TCAS II provides both TAs and resolution advisories (RAs) to prevent a collision by commanding the pilots to execute an avoidance
maneuver in the vertical direction [5]. TCAS II version 7.1 is the
system that is currently in use, and we use the scenario of three
TCAS-equipped aircraft in Figure 1 to illustrate its basic operations.
In normal flight, Aircraft 1, Aircraft 2, and Aircraft 3 constantly broadcast inquiries and receive answers from neighboring
aircraft to monitor the surrounding airspace. Range and altitude
tests are carried out on each neighboring intruder. If the time to the
closest point of approach (CPA) in both the horizontal and vertical
planes meets the temporal threshold and/or the spatial threshold
for protected airspace (distance modification (DMOD) and altitude
threshold (ZTHR)) in slow-closure-rate encounters (time criteria
values are not appropriate), the intruder is declared to be a threat
[6]. These temporal and spatial values vary with different sensitivity levels (SLs) classified based on the altitude [6]. When Aircraft
1 and Aircraft 2 intrude upon each other's air space and a collision
is predicted to occur within 45 seconds (depending on altitude), a
TA is issued synchronously in each aircraft. Using the TA, TCAS
aims to draw the flight crew's attention to the potentially hazardous
situation. It provides both a visual traffic display and an audio alert
to help the crew prepare for any resolution maneuver that may be
required. Subsequently, when and if the situation deteriorates, and
a collision is predicted to occur with 30 seconds (depending on
altitude) an RA would be issued in Aircraft 1 and Aircraft 2. With
communication between the TCAS aboard each aircraft to ensure
complementary vertical maneuvers, the RA could be passive (i.e.,
maintain) or active (i.e., climb/descend), depending on the situation. The pilots are expected to react calmly and in a timely manner
within 5 seconds after issuance of the advisory. In this situation,
Aircraft 1 descends while Aircraft 2 climbs to achieve a safe sepa-

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