Aircraft Surveillance Systems

Radar Limitations and the Advent of the Automatic Dependent Surveillance Broadcast

Busyairah Syd Ali

• Publisher: Routledge
• Year: 2017
• ISBN:
  9781317183181
• Edition: 1
• Topic: Business
• Subtopic: Business General
• Index: Business

The Communication, Navigation and Surveillance (CNS) systems provide air traffic controllers with the information necessary to ensure the specified separation between aircraft and efficient management of airspace, as well as assistance to flight crew for safe navigation. However, the radar systems that support air traffic management (ATM), and in particular air traffic control (ATC), are at their operational limit. This is particularly acute in the provision of the ATC services in low altitude, remote and oceanic areas. Limitations in the current surveillance systems include unavailability of services in oceanic and remote areas, limited services during extreme weather conditions, and outdated equipment with limited availability of spare parts to support system operation. These limitations have resulted in fatal accidents.

This book addresses the limitations of radar to support ATC in various operational environments, identified and verified by analysing five years of safety data from Avinor, the Air Navigation Service Provider (ANSP) in Norway. It derives a set of taxonomy and from this develops a causal model for incident/accident due to limitations in the surveillance system. The taxonomy provides a new method for ANSPs to categorize incidents while the causal model is useful for incident/accident investigations. The book also provides theoretical justifications for the use of Automatic Dependent Surveillance Broadcast (ADS-B) to overcome the limitations of radar systems and identify areas of improvements to enable seamless ATC services.

Written in a style that makes it accessible to non-specialists, Aircraft Surveillance Systems will be of interest to many in the field of aviation, particularly ATM, safety and accident/incident investigation. It will also offer a useful reference on this vital topic for air traffic management courses.

1 Communication, Navigation, Surveillance and Air Traffic Management (CNS/ATM)

1.1. Background

Conventional air navigation systems such as radars, Instrument Landing System (ILS), VHF Omnidirectional Radio Range and Distance Measuring Equipment (VOR/DME), used for airspace surveillance, navigation and communication are ground-based systems. However, these systems suffer from a number of drawbacks including accuracy limits, range and line-of-sight limitations, being site-critical, the requirement for many installations and the considerable expense required for acquisition and maintenance. While significant advances have been made in hardware and software, the technology principle employed is typically more than 60 years old. Furthermore, these systems are unable to evolve to meet increasing traffic demands around airports, and are difficult to implement over large parts of the earth for example, because of remoteness and inhospitable terrain.

In 1983, the International Civil Aviation Organization (ICAO) gave the task of studying, identifying and assessing new concepts and technologies in the field of air navigation, including satellite technology, to a special committee. The Future Air Navigation Systems (FANS) Committee gathered together aviation specialists from around the world. In such a global forum, these specialists developed the blueprint for the system that would meet the needs of the aviation community well into the next millennium (ICAO, 1998a). The FANS concept, which came to be known as the Communication, Navigation, Surveillance and Air Traffic Management (CNS/ATM) system, involves a complex and interrelated set of technologies, largely dependent on satellites, in order to overcome certain limitations of the existing systems. By adopting an approach whereby satellites would play a major role in communication, navigation and surveillance, the FANS Committee determined that states could substantially increase signal coverage over large parts of the earth with fewer infrastructures.

ICAO in 1992 endorsed CNS/ATM as the sole air navigation services (ANS) system for global application (ICAO, 1998b).

1.2. Communication, Navigation, Surveillance and Air Traffic Management (CNS/ATM)

ICAO defined CNS/ATM as “Communication, Navigation and Surveillance systems, employing digital technologies, including satellite systems together with various levels of automation, applied in support of a seamless global air traffic management system” (ICAO, 2000). The aim of CNS/ATM is to develop a comprehensive and unified system to support the provision of Air Traffic Services (ATS) to meet growth in air travel demand with associated improvements in safety, efficiency and regularity of air traffic, providing the desired routes to the airspace users, and homogenizing the use of equipment in different regions. CNS/ATM is underpinned by a high level of automation which reduces the dependency on the human and eliminates the current constraints to optimize the airspace. The distinct features of CNS/ATM are (ICAO, 2000):

• mix of satellite and ground-based systems – which enable internetworking for data transfer of communication, navigation and surveillance systems from technical sites to operational units to provide complete situational awareness to controllers and pilots;

• global coverage – which enables complete ATC services despite the geographical structure obstacles;

• seamlessness – whereby continuous and reliable services are available without fail to ensure safety;

• interoperable systems – whereby the system is designed as redundant architecture to provide uninterrupted services;

• use of air-ground data link – which enables synchronized situational awareness to controllers and pilots;

• use of digital technologies – to mitigate the limitations of analogue technologies such as noise interruption and to adapt to new digital application systems;

• various levels of automation – whereby more computer applications are used to aid controllers and pilots to perform the various job functions.

Figure 1.1 depicts the paradigm shift in ATM technologies, from the current CNS systems to the new CNS/ATM systems that are a mix of satellite technology and the best of the line-of-sight systems. The new technologies have the potential to support advanced ATM applications such as Cockpit Display of Traffic Information (CDTI) (ICAO, 2003a) that provides situational awareness to pilots and In-Trail Procedure (ITP) (EUROCONTROL, 2009a) to give an aircraft more flexibility for efficient navigation especially in oceanic en-route areas. This in return benefits the airlines in terms of fuel consumption and most importantly reduces the environmental effects (Federal Aviation Administration, 2012). New supported applications are discussed in Chapter 4.

Figure 1.1 Paradigm shift in ATM technologies.

Source: modified from Vismari and Camargo, 2005.

ICAO has developed a Global CNS/ATM Plan (ICAO, 2002a). Contracting states are to develop and implement a National CNS/ATM Plan (ICAO, 2000) based on the ICAO Global Plan. For a period, current technology systems will co-exist with CNS/ATM systems until the transition to CNS/ATM is complete. The main elements of CNS/ATM are addressed in the following sections.

1.2.1 Communication

People and systems on the ground must communicate with the aircraft during all phases of flight. Good communications with timely and dependable availability are the cornerstone of operational safety and efficiency. Currently communication is primarily by means of voice. However, such analogue transmissions suffer from a number of shortcomings: they do not permit high rates of transmission of data and take up a great deal of valuable and diminishing frequency spectrum. This limits automation of routine functions and consequently the decision-making process for both the pilots and controllers.

In CNS/ATM systems, communications will increasingly be carried out using digital data links as these allow a high rate of data transfer, high reliability and integrity, improved frequency spectrum utilization and crucially, better interfacing with automated systems. There are two types of communication systems in place; air-ground communication and ground-ground communication. The current air-ground communication system relies on Very High Frequency (VHF), High Frequency (HF) and Ultra-High Frequency (UHF) analogue data links (radio frequency) for en-route and terminal areas, and Aeronautical Mobile Satellite Service (AMSS) for oceanic and remote continental airspace (ICAO, 2000), while the ground-ground communication relies on VHF data link. According to Hansman (1997), the current flight procedures and route structures have been developed and named based on the voice communication capabilities over low bandwidth VHF and HF links, resulting in limited coverage. Figure 1.1 shows the evolution of the communication technologies.

Future communication systems are based on digital data links such as High Frequency Data Link (HF DL), VHF Data Link Mode 4 (VDL-Mode 4), Mode S Extended Squitter and Universal Access Transceiver (UAT). Data link technologies enable uplink and downlink of four dimensional (4D) waypoints (latitude, longitude, altitude, time) and other data to pilots and controllers. Controller-Pilot Data Link Communication (CPDLC) is an example of a data link application that relies on HF DL, VDL and satellite communication (SATCOM). The implementation of the digital data links has the potential to change the communication of control instructions in the event of analogue voice link failure (Hansman, 1997).

Moreover, the analogue voice communication is prone to many limitations to the users, e.g. limited coverage, accessibility, capability, integrity and security. The voice communication performance, based on the radio frequency can reduce due to interference issues, frequency congestion and noise. This can happen, even though there are specific aviation frequency bands allocated for the ATC use. In addition, due to the different accents of the pilots and controllers, voice communication can lead to misinterpretation of information, which may cause undesired incidents. Despite its limitations, voice communication via radio frequency is still the main mode of communication between pilots and controllers in the ATC environment. Voice communication channels are regarded essential for ATC, since they act as a backup during the worst case (unavailability of surveillance and navigation functions) to enable continuous air traffic services to the users.

The implementation of enhanced modes of data link is envisioned to overcome the limitations discussed above. Therefore, the need for reliable digital data link technologies is crucial. However, the new digital communication technologies have to comply with the Required Communication Performance (RCP) (ICAO, 2006c) set by ICAO. The future communication systems in ATM are envisioned to be a mix of voice and data communication via high-speed digital data links.

1.2.1.1 Aeronautical Telecommunication Network (ATN)

The first step in implementing CNS/ATM, is the establishment of an efficient networking system for the communication of different forms of data, including text, radar, graphics and voice. This requires the use of a combination of terrestrial and satellite-based systems. The current system, the Aeronautical Fixed Telecommunication Network (AFTN), does not have the capability to support the future data requirements of CNS/ATM (ICAO, 2000). Therefore, ICAO proposes the use of the Aeronautical Telecommunication Network (ATN) that comprises application entities and communication services. These make the ground elements, air-ground networks and airborne data networks interact via the International Organization for Standardization (ISO) Open System Interconnection (OSI) reference model based protocol and services interface (ICAO, 1999a). ICAO has standardized the following data links in the context of ATN (ICAO, 1999c):

• Aeronautical Mobile Satellite Service (AMSS), using satellites for communication, both geostationary and non-geostationary satellites, allowing communication by voice and data on a global range.

• VHF Data Link (VDL), using techniques of data communication in VHF bands. They are of types Mode 2, Mode 3 and Mode 4 with differentiation by their characteristics of modulation, control for access to the physical environment and, especially, data transfer rates.

• Mode S Extended Squitter (ES), operating on 1090/1030 MHz to communicate data in a bidirectional manner between air and ground elements with nominal rates of 4 Mbits/s (uplink) and 1 Mbits/s (downlink) (ICAO, 1998b).

• Universal Access Transceiver (UAT), a broadcast data link operating on 978 MHz, with a modulation rate of 1.041667 Mbps (ICAO, 2009).

• HF Data Link (HFDL), which is the union between the characteristics of long-range electromagnetic propagation in the HF spectrum and digital data modulation, providing data communication in remote areas.

Vismari (2007) illustrates the CNS/ATM communication environment based on the ATN in Figure 1.2. ICAO categorized the application entities (AE), which are the functionalities of the ATN used by end systems (ES) in the air traffic system, into air-ground application entity and ground-ground application entity (ICAO, 1999a). The air-ground AE enables communication between ES on the ground (ATS units) and ES in the air (aircraft). Examples of applications in this category include:

• Automatic Dependent Surveillance Broadcast (ADS-B), which provides the aircraft position and other important information to the ES;

• Controller-Pilot Data Link Communication (CPDLC), which provides the ability to establish a peer-to-peer message communication between pilots and controllers;

• Flight Information Services (FIS), which allows pilots to request and receive flight information services; and

• Traffic Information Service Broadcast (TIS-B), which transmits radar surveillance information from the ground to the aircraft in the air.

The ground-ground AE allows communication between ES on the ground (ATS units). The AE in this category are the ATS Message Handling Service (ATSMHS), enabling the exchange of messages between ATS end users; and the Inter-Communication Centre (ICC), which provides message communication between ATS centres for notification, coordination and transfer of control activities.

Figure 1.2 CNS/ATM communication environment.

Source: modified from Vismari, 2007.

An application developed based on the ATN is SESAR’s and Next-Gen’s System Wide Information Management (SWIM) (SESAR Joint Undertaking, 2011). SWIM is a holistic approach enabling information sharing including flight information, weather, aeronautical information and surveillance information among the stakeholders and the airspace users using a secure and flexible system (an intranet). SWIM infrastructure, over which the data are distributed, is interoperable (ground/ground and air/ground). Its data communication link may differ from one user to another depending on available facilities. For SESAR’s SWIM, the PAN European Network System (PENS) will provide the ground/ground data link.

1.2.1.2 Required Communication Performance (RCP)

The communication function is one of the important elements of the ICAO’s Future Air Navigation System – FANS concept (ICAO, 2007b). The Required Communication Performance (RCP) concept ensures that the communication system performance implemented within the ATM system is acceptably safe and reliable to operate in the ATM operational environment. It also includes the ATC ground equipment and aircraft equipage requirements for communication. The RCP concept is applicable to any communication capabilities to support the ATM functions despite technology type. Hence the concept can be applied to any new communication technology. The RCP concept assesses operational communication in the context of an ATM function, taking into account human interactions, procedures and environmental characteristics (ICAO, 2006c).

According to National Aeronautics and Space Administration (NASA), the concept enables diverse communication technologies to be measured in terms of communication process time (i.e. delay), integrity, availability and continuity of function (NASA, 2000). Therefore the concept provides means to quantify the communication system performance, essential to ensure the system safety. However, ...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright page
• Table of Contents
• List of figures
• List of tables
• List of abbreviations
• 1 Communication, Navigation, Surveillance and Air Traffic Management
• 2 Air Traffic Control (ATC) surveillance environment
• 3 Radar system limitations
• 4 Automatic Dependent Surveillance Broadcast (ADS-B)
• 5 Safety improvement potentials with ADS-B
• 6 ADS-B security
• 7 Conclusion
• Bibliography
• Index