Communications, navigation, and surveillance are essential technological systems for pilots in the air and air traffic controllers on the ground. They facilitate the process of establishing where the aircraft is and when and how it plans to arrive at its destination. It also facilitates the process of identifying and avoiding potential threats, e.g., potential conflicts with other aircraft or incoming storms. In order an aircraft to fly from one point to another in a safe way, it must keep continuos contact with the control services on earth by means of communication systems, it must use the navigation systems to continuously determine its position and address to the desired destination. In this whole process, the control services must use the surveillance systems to monitor aircraft and avoid any potential hazard.
The communications are utilized to issue aeronautical information and provide flying aircraft with air transit services. The air transit services are provided form the different control centers (in which air traffic controllers operate), which communicate with aircraft to give instructions, or simply to inform about potential danger. On the other hand, aircraft must use the proper communication equipment (radios, datalink) to receive this service (by receiving this service it is meant to maintain bidirectional communication with control centers). Besides the communication aircraft-control center (the so-called mobile communications), there must be a communication network between ground stations, i.e., control centers, flight plan dispatchers, meteorological centers, etc. More details about the communication service will be given in Section 11.2.
The navigation services refer to ground or orbital (satellites) infrastructures aimed at providing aircraft in flight with information to determine their positions and be able to navigate to the desired destination in the airspace. As already described in Chapter 5, the aircraft will have the required on-board equipment (navigation instruments and displays) to receive this service. More details about the navigation systems will be given in Section 11.3.
The objective of the surveillance infrastructure is to enable a safe, efficient, and cost- effective air navigation service. In airspaces with medium/high traffic density, the function of surveillance requires the use of specific systems that allow controllers to know the position of all aircraft that are flying under their responsibility1 airspace. This service has been typically provided by radar stations in the ground. In this way the evolution of aircraft is monitored and potential threats can be identified and avoided. An instance of this would be two aircraft evolving in such a way that a potential conflict2 is expected in the mid-term. The controller would advise instructions (using the above mentioned communication system) to the involved aircraft to avoid this threat. Automatic Dependent Surveillance-Broadcast (ADS-B) will be replacing radar as the primary surveillance method for controlling aircraft worldwide. There are also airborne systems that fulfill a surveillance function. That is the case of the Traffic Collision Avoidance System or Traffic alert and Collision Avoidance System (both abbreviated as TCAS). More details about the surveillance systems will be given in Section 11.4.
1. Notice that each control center has the responsibility over a volume of airspace.
2. In air navigation, a conflict is defined by a loss of separation minima. This separation minima is typically defined by a circle of 5 NM in the horizontal plane and a vertical distance of 1000 ft.