CNS/ATM technical support

Air Traffic Management today is unthinkable without special technical facilities. The requirements established by International Civil Aviation Organization (ICAO)  (  for aviation technical systems, are very stringent.

The main requirements established for technical support are: high reliability, redundancy, accuracy of parameters, continuous monitoring of systems, operational information recording, data integrity and high information security. High quality technical support is based upon the respective maintenance system and the competencies of the technical personnel.

According to their operating principles all aviation systems can be divided into the so-called conventional, that are still in use, and CNS/ATM (Communication, Navigation, Surveillance and Air Traffic Management) technology based (the ICAO term is FANS – Future Air Navigation Services) systems – their extensive implementation has been recently started.  The main difference between the systems is that CNS/ATM Systems are based upon data exchange networks and satellites and therefore, their potential is huge, whereas the conventional equipment cannot cope with the forecasted traffic growth nor ensure the required capacity and accuracy of the air traffic management system.

Two major programmes  are established for developing and implementing new technologies: SESAR in Europe and NexGen in the US. The European Commission regulation 552/2004 shall be followed for ensuring the systems interoperability. The implementation of several technologies in Europe is regulated by Implementing Rules ensuring simultaneous and harmonised activities in the European region.

High quality technical support is based upon the respective maintenance system and the competencies of the technical personnel. CNS/ATM Department of EANS is responsible for the operability of CNS/ATM – communication, navigation and surveillance – systems in accordance with the main requirements.



Communication in aviation is 

Radio voice communications (air-ground voice communication),   for exchanging instructions, acknowledgements and other messages between pilots and air traffic controllers.

Radio transmitter and receiver are geographically separated from each other – it is for achieving better signal quality. Some radio relay stations installed in different locations enable radiocommunications in Estonian airspace even at lower altitudes; all of them are integrated into a common network. Every ATS unit has a separate, designated to it, radio frequency. Taking into account the importance of radio communication, it is not limited to one radio network, but each radio frequency in use has a separate back-up radio station.

In 2017 the voice communications will be replaced by  CPDLC (Controller Pilot Data Link Communication), but voice transmissions will still remain a back-up means.

  • Ground communication system  (ground-ground voice communication)includes all telephone lines and other direct channels linking neighbouring ATS units and Centres, where information exchange requires voice communication. EANS has regular channels with ATC Centres in Finland, Latvia, Russia and Sweden.
  • TDM-technology is being replaced by IP based data exchange. Nowadays there is a trend in the world to replace point-to-point channels with corporate IP-based data exchange networks. Companies invest more and more in VoIP technologies to be used between air traffic control units and radio stations.
  • Air-Ground data communication is part of the CNS/ATM technology, where the information/data exchange applications (including instructions) use either VDL (VHF Data Link) or Mode S extended squitter technology accordingly. The idea is to use the limited resources of radio frequencies in a more efficient way, to exchange the continuously increasing amount of information and messages, to update the information more frequently and to reduce misinterpretation of the transmitted information.
  • Ground-ground data communication is one of the key elements of CNS/ATM technology. In the future WAN (wide area networks) will replace the point-to point voice channels between different ATS units. Even nowadays data exchange networks are used for different purposes – systems’ remote control, surveillance data exchange, exchange of flight messages – AFTN/AMHS, aeronautical information exchange – although their networks are not yet fully integrated into a common system. In Europe there is a EROCONTROL initiated newPENS procurement (PENS – Pan European Network Service), which is meant to meet the above mentioned needs for information exchange.


For navigating in the air, aircraft in flights need to know accurate information regarding their position and the fixed points to head for. Where good navigation networks are available, flight crews can navigate in the required direction without continuous assistance of air traffic controllers.

The information required for classical navigating can be conditionally divided into:  direction and distance  from a known point. Among others, this information is transmitted to aircraft from the ground-based network of navigation aids, which, in case of Estonia, consists of direction beacons: VORs – VHF Omnidirectional Radiobeacon, NDBs Non-directional Radio beacon and DMEs – Distance Measuring Equipment). NDBs and VORs are gradually becoming “things of the past” – they are still used at aerodromes only.

The airborne equipment receives information from several navigation aids simultaneously and, based on it, determines the aircraft position in the air.

But already now satellite-based navigation GNSS elements are widely used, GPS system being most popular. GNSS procedures are based on such systems like ABAS (Aircraft-Based Augmentation System), SBAS (Satellite-Based Augmentation System – WAAS, EGNOS), GBAS (Ground-Based Augmentation System).


Surveillance aids are used for creating the real situational airspace picture. The major subgroups are radars, ADS and multilateration systems:

  • According to their working principle the radars can be divided into primary and secondary ones; the secondary radars are most used in civil aviation.
  • Primary radars (PSR – Primary Surveillance Radar) display echoes reflected by all moving objects, including aircraft, and some meteorological phenomena. In Estonia one Primary Radar is used for monitoring aerodrome traffic movements and combined Primary Radars information is used for air traffic control in cooperation with Estonian Air Force
  • In Secondary surveillance radars (MSSR – Monopulse Secondary Surveillance Radar) a set of radio interrogations is transmitted by a ground interrogator to airborne transponder, whichafter formatted response is forwarded to the ground based radar station. Estonia has two of them:  in the vicinity of Tallinn and in the western part of the country. The Secondary surveillance radars in Finland and Latvia also contribute to the complete situational picture of the Estonian airspace.
  • Mode S (Mode Select) radar is an advanced secondary radar. This radar allows to interrogate transponders selectively (also different interrogations to different transponders); the data exchange is digital and it is considerably more accurate compared to previous ones; through the transponder it is possible to transmit readings of different airborne systems.
  • With the help of ADS (Automatic Dependent Surveillance) the airborne equipment sends GPS data to the ATC Centre through data-base exchange channels. These data are processed and added to the overall picture of the situational picture of the airspace. In Estonia ADS-B receivers are part of the ACC WAM (Wide area Multilateration system).
  • MLAT (MultiLATeration) is a modern equivalent of old hyperbolic triangulation systems. In MLAT four or more receivers, positioned at respective sites, receive aircraft transponder signals. The time of signal reception is fixed with high accuracy by a central processor, which derives computations on the precise 3D position of aircraft (transponder).
  • In Estonia two MLAT systems are in use – one for monitoring ground movements at Tallinn aerodrome and the second one is WAM (Wide Area Multilateration), covering entire Tallinn FIR, – it also provides the receipt of Mode-S messages.

The surveillance sources are numerous, whereas air traffic control requires a complete picture of entire airspace with all the necessary information, therefore, the information from different sources is assembled to make an integral picture with the help of surveillance data processing and sharing systems.

  • The surveillance data processing and sharing system (tracker) is used in Estonia as two independent systems: ARTAS – ATM suRveillance Tracker And Server and MSTS – Multisensor Tracking System, and in case one of them is unserviceable it is automatically replaced with the other one. 


The data from all technical facilities are assembled in the air traffic control centre, verified, processed and, finally, forwarded to air traffic controllers. The most crucial of these systems are:

  • VoiceCom System (VCS – Voice Communication System) – integrates all incoming and outgoing voice channels, radio and emergency lines and provides user-friendly manipulation for controllers;
  • FDPS – Flight Data Processing System is used for processing all the data regarding the traffic situation in the airspace;
  • SDPS – Surveillance Data Processing System is used for surveillance data processing and creating the real situational picture of the airspace;
  • ODSOperational Display System together with Safety Nets and Flight Monitoring software helps reduce potential conflicts;
  • NM (Network Manager) Traffic Flow planning tools;
    Õhuruumi korraldamise vahendLARA  Local And sub-Regional Airspace Management System (LARA)
  • Common Clock System;
  • Recording and Replay Systems.


The following technical solutions are supporting? the provision of air navigation services:

  • additional information system for ATCOs;
  • flight plan preparation;
  • extraction of information about routes and meteorological conditions;
  • electronic aeronautical information preparation, exchange and dissemination;
  • system testing environment.

CNS/ATM Department is also responsible for developing or setting-up EANS business supporting software environments and tools:

  • Staffing Planner Tool;
  • post-flight data processing, billing system;
  • staff training;
  • development process, projects and change management;
  • report handling;
  • CNS assets and technical files handling.