Commercial aviation requires the use of safe and efficient air navigation and communications systems. Such systems allow piloting an aircraft between destinations without endangering the safety of passengers and breaking the laws associated with aircraft travel. Effective and precise navigation and communication systems have become invaluable instruments in the modern aviation world because there are thousands of commercial aircraft aloft at any moment, which prevent the use of dead reckoning.
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This paper aims to explore the navigation and communication systems used in modern commercial aviation. The paper will focus on satellite navigation systems and Controller Pilot Data Link Communications (CPDLC) systems. The purpose, main components, functioning, benefits, and limitations of these navigation and communications systems will also be explicated.
Since the first manned flight demonstrated by Orville and Wilbur Wright, aviators have been seeking ways to improve the safety and functionality of flight (Madry, 2015). In less than a century, countless attempts to secure air travel resulted in the development of reliable and precise communication and navigation systems (Madry, 2015). Nowadays, when there are thousands of commercial aircraft such systems are key components of safe and efficient flight. This paper aims to explore commercial aircraft navigation and communication systems. The paper will focus on satellite navigation systems and CPDLC systems.
Satellite Navigation Systems
A satellite navigation system or a sat-nav system can be defined as a system of satellites that are used for the provision of autonomous geo-spatial positioning (Grewal, Andrews, & Bartone, 2013). Geo-spatial positioning refers to “a specific location on or above the Earth in three dimensions” (Linx, n.d., para. 3). Early sat nav systems “relied on Doppler shift as a low-Earth orbit satellite moved across the sky” (Pelton & Madry, 2013, p. 563).
However, the invention of atomic clocks has facilitated the development of new, extremely precise navigation systems. Modern sat-nav system receivers used in commercial aircraft are not only capable of analyzing geo-spatial data such as latitude and longitude, but they also provide altitude and velocity information (Pelton & Madry, 2013). A network of contemporary, high-end satellites is accurate to within several meters (Pelton & Madry, 2013).
Sat nav systems have found applications in the transport industries. In the aviation sector, the most commonly used sat-nav system is a three-dimensional global navigation satellite system (GNSS). GNSS is the umbrella term for global sat nav systems; however, there are only two global systems in the world: Global Positioning System (GPS) and GLONASS. GPS is the U.S.-owned system that is comprised of 32 interconnected satellites (Madry, 2015).
The system has been developed by the U.S. Department of Defence and can be used for receiving geolocation and time information anywhere on the Earth. GLONASS or Global Navigation Satellite System is a system developed by the Russian Aerospace Defence Forces. Unlike GPS, GLONASS has only 24 satellites and 3 orbital planes; therefore, it is associated with lower positioning accuracy (Madry, 2015).
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Two global satellite navigation systems are currently in the development stage: Galileo (EU) and Compass (China). Regional satellite navigation systems include the BeiDou Navigation Satellite System (BDS) (China), Quasi-Zenith Satellite System (QZSS) (Japan), and the Indian Regional Navigation Satellite System (IRNSS) (Madry, 2015).
Components and Operation
Satnav systems are composed of three major elements: the space segment, the control segment, and the user segment (Lu, Peng, Miller, Zhao, & Johnson, 2015). The space segment of GNSS systems consists of an interconnected group of navigation satellites. Satellite constellations guarantee that at least four satellites are observed simultaneously, thereby ensuring that nothing disturbs the propagation of satellite signals (Madry, 2015).
The space segment has four functions that help to create uninterrupted real-time navigation. The first function is to continuously transmit uninterrupted signals that can be received by the user segment. These signals include the pseudo-range, the exact time, the distant measurements, and navigation messages (Lu et al., 2015). The second function of the space segment is to receive messages transmitted by a ground antenna.
The messages are sent via a specific band at the moment when a satellite passes above an antenna (Lu et al., 2015). The third function is to “transmit and receive satellite commands from the master control station through the ground antenna” (Lu et al., 2015, p. 96). The fourth function of the space segment is to control the power supply of navigation satellites.
The control segment of sat nav systems is comprised of the following segments: monitor stations, master control stations, and ground antennas (Madry, 2015). The segment is a group of monitoring and measuring systems that are necessary for the proper functioning of satellites. The control segment performs four functions:
- monitors satellites;
- tracks and calculates parameters of satellites’ orbits;
- synchronizes satellites’ clocks;
- computes scheduling for satellites (Lu et al., 2015).
In the control segment of a sat-nav system, only a master control station is manned; ground antennas and monitor stations are unstaffed (Lu et al., 2015).
The user segment consists of the following parts: “system software, a navigation system receiver, a computer, and metrological equipment” (Lu et al., 2015, p. 97). The main elements of a receiver are “the controller, host, power supply, and antenna” (Lu et al., 2015, p. 97). A navigation system receiver performs four functions:
- receives satellite signals and analyses their orbits with the help of cut-off angles to calculate the position of a user;
- converts and computes data to calculate the time of transmission;
- calculates the velocity of a user;
- provides a user with data through a visual interface (Madry, 2015).
Benefits and Limitations
Commercial aircraft that rely on satellite navigation systems are benefiting from saving fuel and thereby reducing their environmental impact (Enge, Enge, Walter, & Eldredge, 2015). According to Enge et al. (2015), satellite navigation systems enable “performance-based navigation, which consists of area navigation (RNAV) and required navigation performance (RNP)” (p. 19). By relying on these capabilities of GNSS commercial aircraft can use point-to-point flight routes that are not restricted to paths provided by ground-based radio navigation (Enge et al., 2015).
Sat nav systems allow aircraft to reduce distance with each other, thereby increasing both arrival and departure rates (Enge et al., 2015). Despite all these benefits, GNSS systems are associated with some limitations “which affect the coverage, accuracy, and reliability of the satellite measurements” (Grewal et al., 2013, p. 47).
Modern air traffic control (ATC) cannot function without effective communication between ground control and pilots (Landry, 2013). However, existing voice technologies are associated with numerous limitations. According to Landry (2013), the drawbacks of voice communication technologies include, but are not limited to, interference, cross-talk, translation challenges, and exceptionally complicated tasks that have to be performed by a controller. To address these limitations, Controller Pilot Data Link Communication (CPDLC) systems have been created. CPDLC is a technology that “replaces traditional voice-based radio communications between pilots and controllers with a text-based data link” (Landry, 2013, p. 130).
The first CPDLC systems were introduced in 2002 to replace the majority of verbal communication systems by 2025 (Nolan, 2015). The purpose of the technology is to “provide clearances, information items, pass along requests, or otherwise communicate with the pilots of an aircraft” (Landry, 2013, p. 130). Datalink capabilities of the system allow structuring communications into a series of text messages. These messages can be delivered in pre-formatted and free text formats. Pre-formatted message sets can be used to respond to clearances or request information with the help of standard ATC phraseology (UASC, 2013).
By transmitting text-based communications with aircraft across different ATC sectors, it is possible to substantially reduce costs of connectivity with aircraft (Mahmoud, Guerber, Larrieu, Pirovano, & Radzik, 2014). The use of CPDLC systems is especially common in non-radar airspaces (UASC, 2013).
Components and Operation
Two standards are allowing the implementation of CPDLC. Future Air Navigation Systems (FANS)-1/A makes possible the use of CPDLC via the Aircraft Communications Addressing and Reporting System (ACARS) (Nolan, 2015). The standard is primarily used in long-haul oceanic flights (Nolan, 2015). Aeronautical Telecommunication Network (ATN)-CPDLC allows the deployment of the technology in the Maastricht Centre (Nolan, 2015).
The implementation of CPDLC systems is the process that requires the participation of the following actors: aviation authorities, air transport industry, DSP and communication service providers, and technology users (Mahmoud et al., 2014).
Aviation authorities such as standard-developing organizations (SDOs) develop principles and standards of international air navigation. EUROCAE and RTCA are SDOs that work in close partnership with national authorities to guarantee the safe and efficient use of CPDLC systems (Mahmoud et al., 2014).
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The second group of actors involved in the deployment of CPDLC systems is the air transport industry, which includes communication equipment suppliers and aircraft manufacturers (Mahmoud et al., 2014). The industry is involved in the design, production, and installation of equipment for CPDLC systems. To ensure that aircraft are properly modified for CPDLC capabilities, the air transport industry closely cooperates with aviation authorities.
The third group of actors involved in the implementation of CPDLC systems is data link service providers (DSPs) or communication service providers (Mahmoud et al., 2014). These organizations ensure that transmission media functions properly, thereby guarantying the integrity of communication. DSPs are involved in the creation of multiple data links necessary for the transmission of messages between aircraft and ground (Mahmoud et al., 2014). DSP services are provided by several companies; however, the providers with the largest communication networks are ARINC and SITA. These companies operate “a network of ground stations that are generally located at airports and other sites” (Mahmoud et al., 2014, p. 7).
The fourth group of actors is technology users. This group includes air navigation service providers (ANSPs) such as government departments, private organizations, and airlines.
In terms of equipment installation for CPDLC systems, the following components are necessary for the modification of an aircraft for CPDLC capability: compatible radios (VHF, SATCOM, HFDL), compatible ACARS, MU/CMU, dual GPS, flight management system (FMS) with appropriate software version, printer supporting FMS, and flight data recorder (DCA, 2013).
Benefits and Limitations
There are several differences between voice communications and messages via CPDLC systems. Even though ATC clearances and other messages delivered over voice are fast, they are transient. In other words, after the transmission of a message is finished, a pilot loses the opportunity to process it (Lennertz & Cardosi, 2015). Unlike voice communications, messages delivered via CPDLC systems are permanent and can be accessed by pilots as often as needed.
The use of text messages also precludes pilots from “erroneously accepting a clearance intended for another aircraft by misidentifying the call sign” (Lennertz & Cardosi, 2015, p. 3). The use of CPDLC systems eliminates issues associated with language barriers, thereby making communications more accurate. Furthermore, technology increases the availability of VRF, which can be used for the delivery of critical clearances (Landry, 2013). The deployment of CPDLC systems automates many communication tasks and offloads controllers.
Despite many benefits of CPDLC systems, there are also some limitations. The technology is more time consuming than voice communications (Landry, 2013). Also, voice messages can be heard by multiple pilots simultaneously, thereby enhancing their situational awareness. Furthermore, some concerns have been raised over communication errors and communication modes preferences (Landry, 2013).
The paper explored the use of navigation and communication systems in modern commercial aviation. Global satellite navigation systems such as GLONASS and GPS that are used for the provision of geo-spatial positioning consist of the space, control, and user segments that provide transmission and reception of signals. CPDLC systems allow transmitting text-based messages, thereby improving traditional ATC function that relies on the use of voice messages.
Enge, P., Enge, N., Walter, T., & Eldredge, L. (2015). Aviation benefits from satellite navigation. New Space, 3(1), 19-35.
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Landry, S. (2013). Advances in human aspects of aviation. Boca Raton, FL: CRC Press.
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Lu, Y., Peng, Z., Miller, A., Zhao, T., & Johnson, C. (2015). How reliable is satellite navigation for aviation? Checking availability properties with probabilistic verification. Reliability Engineering and System Safety, 144(1), 95-116.
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